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DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY 



B'BB 5 87 

WASHINGTON, D. C. -*- — * "^^ ^^ . 188 




QEOLOaiOAL HISTORY OF LAKE LAHONTAN: 

BY L O. RUSSELL. 

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Chief Clerk. 



DEPARTMENT OF THE INTERIOB 



MONOGRAPHS 



United States Geological Survey 



VOLUME XI 




WASHINGTON 

OOVKRNMENT FEINTING OFi'lCB 

1886 



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I 



UNITED STATES GEOLOGICAL SUBVEY 
J. W. POWKI.I, DIRECTOR 



GEOIX)G[CAL HISTORY 



LAKE LAHONTAN 



A QUATKRNARY LAKE OF NORTHWESTERN NEVADA 



ISKAKL COOK RUSSELL 




WASIIINOTON 
OOVEllNRIKNT I'RINTINT. oPFirK 



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Washington, D. C , March 28, 1885. 

Sir: I have the honor to submit for publication a memoir on Lake 
Lahontan by Mr. I. C. Russell. 

The principal work of my Division has been the investigation of the 
Qu.aternary lakes of the Great Basin. In this investigation Mr. Russell has 
been my principal assistant since the year 1880. During the first season 
he accompanied me in the field for the purpose of familiarizing himself with 
the methods of research which had been developed in the course of the 
earlier work, but in subsequent years he was assigned independent districts. 
His report on the most important of these is communicated in the pres- 
ent volume. 

After the completion of his field work, I visited some of the more in- 
structive localities of the Lahontan basin and repeated his observations. I 
am thus familiar not only with his methods but with some of the principal 
facts which he discusses, and am enabled from personal knowledge to char- 
acterize his work as accurate and thorough. 

Very respectfully, your obedient servant, 

G. K. GILBERT, 
Geologist in Charge^ Dlvmmi of the Great Basin. 

Hon. J. W. Powell, 

Director U. S. Geological Survey. 



PREFACE. 



The explorations reported in the present vohime are a continuation of 
the studies of the Quaternary geology of the Great Basin begun by Mr. 
G. K. Gilbert when the present survey was organized. The work has been 
carried out under Mr. Gilbert's direction, and to him I am indebted not only 
for every facility he could offer for advancing my work, but also for im- 
portant advice and numerous suggestions. Whatever value may be at- 
tached to the results of my labors will be due in great measure to the 
wisdom and unvarying kindness of the Chief of the Division of the Great 
Basin. 

With the exception of the reconnaissance of 1881, I have had the 
assistance of Mr. Willard D. Johnson in all matters relating to topography 
throughout both the field and office work connected with the preparation of 
this volume. The energy and completeness with which he has carried for- 
ward his special work under peculiar difficulties, not met with outside the 
desert regions of the Far West, deserve the highest praise l^he accuracy 
of the accompanying maps that Mr. Johnson has drawn from his own sur- 
vey will make them a reliable basis for determining future changes in the 
lakes and rivers of the region explored. 

During the sunmier of 1882, I was accompanied by Messrs. W J Mc- 
Gee and George M. Wright, as geological aids, and to each I have the 
pleasure of crediting nuu^h valuable assistance. The accompanying draw- 
ings of geological sections will attest the accuracy of Mr. McGee's work. 

The survey of nearly 8,500 square miles in northern Nevada, which 

was necessary in order to compile the accompanying pocket map and many 

of the smaller illustrations, was carried out by Mr. A. L. Webster, assisted 

vu 



II 



i I 



I 



Vin PREFACE. 

by Mr. Eugene Kicksecker. It is to be hoped that Mr. Webster's work will 
be issued as an independent atlas sheet, in order that its full value may be 
appreciated. 

Since this report was written the analyses by Prof. F. W. Clarke and 
Dr. T. M. Chatard, contained in the following pages, have been published in 
Bulletin No. 9 of this Survey, to which the reader is i-eferred for additional 
information in reference to methods of analysis. 

I. C. R 



C O N ^r E N T S . 



Letter of Transmittal. . 

Preface 

Abstract of Monograph 



Page. 

V 

vn 
1 



Chapter 1. —Introductory. 

The lieM of study .* 6 

The Great Basiu 7 

Kxploratious 15 

vJhapter II.— Genesis of Lake Lahontan. 

The formation of hicuHtral basins 23 

Orifjiu of the Lahontan basin 24 

Geographical extent of Lake Lahontan 28 

The hydrographic basin 28 

The lake basin 31 

Question of outlet 32 

Chapter III.— I'hysiography of the IjAHONTan Basin. 

Valleys 36 

Mountains 38 

Rivers 40 

The Humboldt 40 

Q'uinn River 41 

TheTruckee 42 

The Carson 43 

The Walker 45 

Springs 47 

Extinct springs 54 

Lakes — 55 

Honey Lake, California 55 

Pyramid Lake, Nevada 56 

Winnemucca Lake. Nevada 63 

Humboldt Lake, Nevada 66 

North Carson Lake, Nevada 68 

South Carson Lake, Nevada 68 

Walker Lake, Nevada 69 

Taboe Lake, Nevada and California 71 

Soda Lakes near Ragtown, Nevada 73 

Playa-lakes and playas 81 



CONTENTS. 






ClIAPTKR IV.— PUYSICAI. IIISTOICY OF LaKK LaIIONTAN. 

Sool i<»n 1 . yhorr ]>heii()iii('iia in •;rii<'ral 

Terraces 



Sea-clitfs 

Bare 

EuibaiikuieiitH 

Deltas 

Recapitulation 

Sect iou 2. Sborc phetioun iia of Lake Lahoutaii 

TerraccH and scii-cliffs 

Bars and enibankmeutH 

Einbauknieuts at tbe went end of Humboldt Lake 

Knibanknients on tbe Koutbern border of tbe Carson Desert . 

Embankments at Buffalo Springs, Nevada 

Deltas 

Section 3. Sediments of Lake Labontan 

Ex^Misures in tbe ca&on of tbe Humboldt River 

Exposures in tbe cafion of tbe Truckeo River 

Exposures in tbe canon of tbe Carson River 

Exposures in the caRon of tbe Walker River 

Generalized (section of Labontan sediments 

Exceptional 8e<limentary deposits 

Pumiceous <luat 

Wbit« marl 

^olian sands 

Section 1. Ancient stream channels 

Section 5. Illustrations of geological st ructure 

Stratification and lamination 

Current bedding 

Contorted strata 

Arches of deposition 

Unconformity by erosion and deposition 

Jointing 

Faults 

St ructure of t4.*rraces and embankments 

Conglomerates and breccias 

Oolitic sand 

Surface markings 

Color of lacustral s<;diments 

R^nm6 of ph.VHical history 

ClIAITKK V — ClIKMICAL HISTORY OK LaKK LaUONTAN. 

Section I. General clieniiKtry of natural waters 

River water 

Spring water 

(Jcean water 

Wat^TH of inland hcjik 

Succi'ssion of salts deposited <»n evaporation 

De])i>Hitioii of calcium carbonate 

S<?ction M. Chemical <lepositH of Lake Lah(»ntaii 

Calcan-ouH tufa 

I^itboi<l tufa 

Tbinolitic tufa 

Professtu- Dana's <:rvKtallograpbie study of tbinolite 
Dendritic tufa 



87 
88 
89 
90 
93 
96 
98 
99 
100 
105 
105 
112 
115 
123 
124 
126 
131 
137 
138 
143 
146 
146 
149 
153 
156 
158 
158 
158 
160 
161 
162 
162 
163 
166 
167 
168 
168 

lee 

160 



172 
172 
175 

178 
181 
182 
187 
188 
189 
190 
19t2 
194 
201 



CONTENTS. XI 

Page 

Chapter V.—Chkmical histouy of Lakk LAUONTAN—Continued. 

Sectiou 2, Chemical deposits of Lake Lalioiitaii— Continued. 

Chemical composition of the tufa deposits 203 

Succession of tufa deposits 204 

Tufa deposi ts in the form of towers, dome«, castles, crags, etc 207 

Conditions lavo?ing the dcpoKition of tufa 210 

Section 3. Desiccation product* 223 

The freshening of lakes by desiccation 224 

Section 4. Efldorescenct's. 230 

Buffalo Springs salt works 232 

Eagle salt works 2:^ 

Sand Spring salt works 234 

R^um^ of chemical history 230 

Chaptbr VI.— Life history of Lake Lahontan 238 

Summai y ...... .^ 249 

Chapter VIL—R<C8UME of history of Lake Lahontan 2W) 

Chapter VIII.— Quaternary CLIMATE 254 

Chapter IX.— Geological age of Lake Lahontan 269 

Chapter X.— Pobt-Lahontan orographic movement ; 274 

Index 286 

4 



TABLES OF CHEMICAL ANALYSES. 

Table A. — Analyses of Au»erii*an river waters 174 

B. — Anal^ ses of American spring waters 176 

C— Analyses of the waters of inclosed lakes l^'O 

D. — Composition of the principal lakes and rivers of the Lahontan basin 225 



ILLUSTRATIONS. 



Page. 

PiJiTE I. — Map of the Great Basin, sliowiny; punition of Lake Labontaii I 

II.— Map of routes of travel and areas surveyed 20 

III. — Map of pre-Qnateniary fault-lines of the Labontau re;;ioH 28 

IV. — Map of t lie water surface and drainage area of Lake Laluuitan IJO 

v.— Map showing depth of Lake Lahontan at hij^hest stage 32 

VI. — Map eshowing land classification of the Lahontan region 'Mi 

VI I. — Map of the Cars(»n Desert, Nevada 44 

VUL — Map of the springs of the Lahontan basin 4^ 

IX. — Map of Pyramid and Winneuiuc<-a lakes, Nevada 50 

X. — Map of Anaho Ihland, Pyramid Lake, Nevada ^)S 

XI. — Sketch of Pyramid Island, Pyramid Lake, Nevjwla (from a photoffraph) W 

XII. — Sketch of the Needles, Pyraiiii<l Lake, Nevada (Jrom a pholofjraph) 62 

XIII. — Sketch among the Needles {from a photof/ruph ) 04 

XIV. — Sketch of Mushroom rock, Anaho Island 60 

XV. -Map of Walker Lake, Nevada 70 

XVI.— Map of the Soda Lakes, near Kagtown, Nevada 74 

XVII. — Sections of the crater walls inclosing the Soda Lakes, Nevada 70 

XVIII. — Map of gravel emhankinents at the west end of Ilumholdt Lake, Nevada 100 

XIX. — Map of gravel embankments on southern border of the Carson Desert, Nevada. 112 

XX. — Map of gravel embankments at Buffalo Springs, Nevada 116 

XXI. — Map of gravel embankments three miles south of Buffalo Springs 118 

XXII.— Humboldt Canon, near Rye Patch, Nevada (from a photograph) 124 

XXIII. — Sections of Lahoiitan sediments in Humboldt Canon, Nevada 126 

XXIV. — Sections of Lahontan sediments in Truekee ('anon, Nevada 132 

XXV. — Sections of Lahontan sediments near Agency Bridge, Truckee Canon 134 

XXVI. — Section of Lahontan sediments at Agency Bridge, Truckee Canon, Nevada.. . 136 

XXVII. — Section of Lahontan wdiments, Truckee Canon 136 

XXVIII.— Sections of Lahontan sediments in Walker River Canon, Nevada 140 

XXIX. — Map of the present drainage areas of the Lahontan basin ir>0 

XXX. — Tufa crag at Allen's Springs, Nevada (/;ow a photograph) 188 

XXXI. — Map of the water surface of Lake Lahontan at the thiuolite stage 192 

XXXII. — A characteristic specimen of thinolit*? (/rom a photograph) 194 

XXXIII.— Illustrations of the structure of thiuolite 190 

XXXIV.— Illustrations of the structure of thiuolite 198 

XXX v.— A characteristic specimen of dendritic tufa {from a photograph) 202 

XXXVI. — Dendritic tufa deposited on a cliff {from a photograph ) 204 

XXXVII. — Imitative tufa forms {from a photograph) 206 

XXXVIII. — An island of tufa in Pyramid Lake {from a photograph) 208 

XXXIX. — Tufa towers on the shores of Pyramid Lake {from a photograph) 210 

XL. — Tufa castle, west shore of Pyramid Lake, Nevada {from a photograph) 212 

XLL — Tufa domes in Pyramid Lake {from a photograph) 214 

Xlil 



XIV ILLUSTRATIONS. 

Plate XLII. — Tnfa tower oti the shore of W inuenuicca Lake {from a photograph) 216 

I XLIII. — Tufa doDies in Mono Lake, California (from a photograph) 222 

XLIV. — Map of podt'Qwaternary faults 274 

XLV. — Post-Quaternary fault on the south shore of Iluuiholdt Lake (from a photograph) 276 
XLVI. — Map of Lake Lahontan (i'm pocket at end of volume). 



1 •■; 



I 



j Fig. I. — Ideal section illustrating Basin Range structure 25 

j ! 2. — Ideal section through the Black Rock Desert, Nevada 27 

3. — Ideal section through the Pahute Range, Nevada 27 

4. — Ideal section through Pyramid and Winnemucca lakes, Nevada 27 

j T). — Ideal section through the Carson River Cafion, Nevada 44 

f G. — Deposits of calcium carbonate from sub-lacustral springs 61 

7. — Map of a portion of the east shore of Pyramid Lake, showing jKisition of measured rocks 65 

8. — Ideal profile of a cut terrace 88 

' 9. — Ideal protile of a cut and built terrace 88 

1 10. — Ideal plat and section illustrating the formation of barrier bars 91 

11. — Ideal plat illustrating the formation of embankments 94 

12. — Diagram illustrating the relative age of gravel terraces and embankments 95 

13. — Ideal section of a high-grade delta 97 

'» 14. —Generalized protile of Lahontan terraces 102 

« If). — Profile of litlioid terrace and Lahontan beach lOlJ 

.J 16. — Profile of gravel embankment at west end of Humboldt Lake, Neva<la 107 

I 17. — Section of embankment at west end of Humboldt Lake, Neviwla 108 

J 18.— Section of bar on the Niter Buttes, Nevada 110 

.j 19. — Map of gravel embankments at south end of Winnemucca Lake 120 

, 20. — Section of gravel embankments at south end of Winnemucca Lake 120 

21. — Sketch-map of gravel umbankments in Churchill Valley, Nevada 121 

22. — Sketch-map of gravel embankments at south end of Quinn River Mountain, Nevada ... 122 

23.— Volcanic dust 146 

24. — Section of White Terrace, west side of Pyramid Lake, Nevada 151 

25. — Rovorao fault in Lahontan gravels 164 

20. — Recent faults in lacustral clays, Humboldt Valley, Nevada 165 

27. — Section of current-bedded gravel between litli<»id and thinolite tufa 191 

J 28. — Diagram showing succession of tufa deposits 204 

•j 21». — Vertical and horizontal 8ecti<ms of a tufa tower 209 

30.— Section of reser voire and vats at Eagle salt works, Nevada 2*.M 

; 31.— Curve illustrating the rise and fall of Lake Lahontan 237 

32. — Larval cases of Caddis lly inclosed in infa 246 

33. — Spear-head of obHidian, from Lahontan sediments 247 

34.— Curve of Lahontan climate; Wetrer«M» Dry 261 

35. — Curve of Lahontan climate; Warm versus Cold 263 

— Idtal cros8-pro6les of fault beds 279 



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GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



BT ISBAEIi C. BUSSEIili. 



ABSTRACT OF MONOGRAPH. 

The present volume records the history of a large lake which flooded 
a number of the valleys of northwestern Nevada at a very recent geolog- 
ical date, but has now passed away. This ancient water-body is known as 
Lake Lahontan — named in honor of Baron La Hontan, one of the early 
explorers of the headwaters of the Mississippi — and was the complement of 
Lake Bonneville. The former, situated mostly within the area now form- 
ing the State of Nevada, filled a depression along the western border of 
the Great Basin at the base of the Sierra Nevada; the latter, embraced 
almost entirely in the present Territory of Utah, occupied a corresponding 
position on the east side of the Great Basin, at the foot of the Wasatch 
Mountains. The hydrographic basins of these two water-bodies embraced 
the entire width of the Great Basin in latitude 41°. Lake Bonneville was 
19,750 square miles in area, and had a maxinuun depth of about 1,000 feet 
Lake Lahontan covered 8,422 square miles of surface, and in the deeptist 
part, the present site of Pyramid Lake, was 886 feet in depth. The ancient 
lake of Utah overflowed northward and cut down its channel of discharge 
370 feet. The ancient lake of Nevada did not overflow. Each of these 
lakes had two high-water stages, separated by a time of desiccation. In 
the Lahontan Basin, as in the Bonneville, the first great rise was preceded 



2 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

by a long period of desiccation, and was followed by a second dry epoch, 
during which the valleys of Nevada were even more completely desert 
than at present. During the second flood stage the lake rose higher than 
at the time of the first high water, and tlien evaporated to complete desic- 
cation. The present lakes of the basin are of comparatively recent date, 
and are nearly fresh, for the reason that the salts deposited when the Quater- 
nary lake evaporated were buried or absorbed by the clays and marls that 
occupy the bottom of the basin. 

As Lake Lahontan did not overflow, it became the receptacle for all 
the mineral matter supplied by tributary streams and springs both in sus- 
pension and in solution. The former was deposited as lacustral sediments 
and the latter as calcareous tufa, or formed desiccation products when 
the lake evaporated. 

The introductory chapter indicates the position of the field of study, 
and contains a sketch of the Great Basin, as the explorer finds it to-day, of 
which the desiccated bed of Lake Lahontan forms a part; also a brief 
notice of previous explorations, and an account of what was known of Lake 
Lahontan before the present study was begun. Boutes of travel and ai-eas 
surveyed are indicated on Plate IL 

Chapter II (on the genesis of Lake Lahontan) contains a summary of 
the facts which show that the lake filled a compound orographic basin, 
resulting from the tilting of faulted beds. A description is given of the 
character of the irregular area whose drainage the lake received, together 
with an account of the outline and area of the basin which held the ancient 
lake. 

The question of outlet is discussed in detail, the conclusion being that 
the lake did not overflow (page 32). 

Chapter III (on the physiography of the Lahontan Basin) contains a 
description of the region as it exists at the present time. The most distinct- 
ive characteristics of the valleys and mountains are briefly noticed ; an 
account of the existing rivers is given, including measurements of volume, 
chemical composition, etc. The present springs of the biisin are also 
desoi'ibed and analyses of the waters of a few of them presented. These 
analyses are believed to represent approximately the character of the tribu- 



ABSTRACT OF MONOGRAPH. 3 

taries of Lake Lahoutan. The existing lakes are next considered. These 
are Honey Lake, California ; Pyraniid, Winnemucca, Humboldt, North Gar- 
son, South Carson, and Walker lakes, Nevada. Each of these is described 
with some detail with spedal reference to its geological bearings. All 
the lakes mentioned above, excepting Humboldt, are inclosed, i. c, are 
without outlet, and their waters ^:"e somewhat saline and alkaline, but not 
concentrated brines. They cannot, therefore, be considered as remnants 
left by the incomplete desiccation of Lake Lahontan. The Soda lakes, 
near Ragtown, Nevada, are specially considered, and detailed observa- 
tions are presented which show tliat they occupy extinct volcanic craters 
(page 73). Attention is given, on page 81, to the peculiar playas or broad 
mud-plains of the arid region of the Far West, as well as to the temporary 
lakes, called playa-lakes, which frequently flood them. 

Chapter IV (on the physical history of Lake Lahontan) is divided into 
sections. 

Section 1 contains a compendious discussion of shore phenomena in 
general. 

Section 2 is devoted to the presentation of the shore phenomena of 
Lake Lahontan, and contains detailed descriptions and maps of the terraces, 
bars, embankments, etc., that were formed about its shores. The highest 
of the ancient water lines is named the "Lahontan Beach." It indicates the 
maximum extent of the lake as shown on the accompanying pocket map. 
The most conspicuous terraces below the Lahontan Beach are the "Lithoid", 
"Dendritic", and "Thinolitic." Each of these marks the upper Kmit of a 
variety of tufa from which it derives its name (page 102). 

Section 3 treats of the sediments of the lake and presents detailed sec- 
tions of the exposures observed. The sediments consist of two deposits of 
lacustral marls, separated by a heavy layer of current-bedded gravels; thus 
recording two lake periods and an intermediate low- water stage (page 43). 

Accumulations of pumiceous dust, white marl, and aeolian sands are 
described under the head of Exceptional Sedimentary Deposits (page 146). 

Section 5 is devoted to the illustration of geological structure, as dis- 
played in the lake basin, and is followed by a r^sum^ of the physical 
history of the lake (page 169). 



4 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

Chapter V (on the cheuiical history of Lake Lahontan) is also divided 
into sections. 

Section 1 treats of the general chemistiy of natural waters as they 
occur in streams, springs, lakes, oceans, and inclosed lakes or seas, and is 
an introduction to the chemical history of Lake Lahontan. 

Section 2 is an account of the tufas precipitated from the water of the 
lake. These present three main divisions, named, respectively, **Lithoid," 
**Thinolitic," and *' Dendritic." The first is a compact, stony variety, and is 
the oldest of the principal calcareous deposits that sheath the interior of the 
basin. It occurs from a horizon thirty feet below the Lahontan beach all 
the way down the sides of the basin to the lowest point now exposed to view 
(page 190). Thinolite is composed of crystals, and was formed in the ancient 
lake when it was greatly reduced by evaporation; its upper limit is about 
400 feet below the Lahontan beach (page 192). Dendritic tufa has a branch- 
ing or dendritic structure, whence its name; it is superimposed upon the 
previously-formed varieties. Its upper limit is 180 feet below the Lahontan 
beach (page 201). The aggregate thickness of the tufa deposits is from 
tliirty to perhaps fifty or seventy-five feet. Chemical analyses show that 
all the varieties are composed of somewhat impure calcium carbonate. Fol- 
lowing the description of these deposits is a discussion of the conditions 
favoring the deposition of calcareous tufa from lake waters (page 210). 

Section 3 considers the salts precipitated from the waters of the lake 
when evaporation took place, and discusses the manner in which lakes may 
be freshened by desiccation (page 223). 

Section 4 contains an account of the efflorescences now forming on the 
surface of the deserts in tlie Lahontan Basin, and presents a brief descrip- 
tion of the more valuable salt-works of the region, which are all supplied 
by the salts contained in Lahontiin sediments (page 230). 

Chapter VI presents the life history of the ancient lake as determined 
from the abundant molluscan remains and other fossils that have been found. 
The shells show that the lake was fresh throughout its higher stages. During 
the period when thinolite was formed it seems to have been too concentrated 
to admit of the existence of molluscan life, as no fossils have been found in 
that deposit. A chipped implement discovered in the upper lacustral beds 



ABSTRACT OF MONOGRAPH. 5 

indicates that man inhabited the Far West during the last rise of Lake 
Lahontan (page 247). 

Chapter VII is a summary of the history of the former lake (page 250). 

Chapter VIII contains a discussion of the Quaternary climate as de- 
termined from the records of Lake Lahontan. The periods of greatest lake 
expansion are correlated with the two glacial epochs of the SieiTa Nevada, 
and are believed to indicate cold and moderately humid periods (page 259). 
That the lake did not overflow is taken as evidence that the climate, even 
during the high stages of the lake, was only moderately humid. The climatic 
changes that brought about such marked alterations in the character of the 
Great Basin are thought to have been of moderate intensity. 

Chapter IX is devoted to a summary of the evidence bearing on the 
determination of the geological age of the lake. The conclusion reached is 
that it existed during the Quaternary, but was more recent than the date 
usually assigned for the close of the glacial epoch. 

Chapter X brings the present study to a close, and contains an account 
of the orographic movements that have affected the Lahontan basin since 
the last high-water period. The post-Lahontan faults actually observed 
are represented on Plate XLV. 



CHAPTER I. 



INTRODUCTORY. 



THE FIELD OF STUDY. 



The region treated of in the present vohime embraces about 90,000 
square miles in northwestern Nevada, together with small portions of south- 
em Oregon and eastern California. 

The object of the explorations herewith reported was the study of the 
Quaternary geology of the country visited, and particularly the geological 
history of Lake Lahontan — a lake, now extinct, which occupied many of 
the valleys of northwestern Nevada at a very recent geological date. The 
basin of Lake Lahontan is one of the many independent drainage areas of . 
which the Great Basin is composed, and its geology is a page in the his- 
tory of the vast region lying between the Rocky Mountains and the Sierra 
Nevada. 

The Great Basin is to-day an arid region, but during the Quaternary 
its climate was probably colder and more humid than at present. The 
Sierra Nevada and Wasatch ranges, now for the most part bare of snow 
during the summer, were formerly (unowned with vast n^v^s from beneath 
which flowed many magnificent ice-rivers; the desert ranges of Utah and 
Nevada were also snow-covered, and some of them gave birth to local gla- 
ciers. The valleys which are now dry and treeless, and in many instances 
absolute deserts, destitute of any kind of vegetation over hundreds of square 
miles, were then occupied by lakes, the largest of which were comparable 
in extent and depth with those now drained by the Saint Lawrence Some 
of these old lakes had outlets to the sea and wore tlio sources of considera- 
6 



SCENIC FEATURES OF THE FAR WEST. 7 

ble rivers, others discharged into sister lakes; a considerable number, how- 
ever, did not rise high enough to find outlet, but were entirely inclosed, as 
is the case with the Dead Sea, the Caspian, and many of the lakes of the 
Far West at the present time. The largest of the Quaternary lakes of the 
Great Basin, thus far explored, has been very fully described by Mr. Gil- 
bert and others under the name of Lake Bonneville. The second in size, 
Lake Lahontan, is the subject of the present report 

The topography of the region to which we wish to direct attention, 
together with its Quaternary hydrography, is represented on the accompa- 
nying pocket map. The relation of the region to the entire area of interior 
drainage, and the more general geography of the Far West, is indicated on 
the frontispiece. Before presenting the results of our geological observa- 
tions it seems desirable to glance briefly at some of the more prominent 
characteristics of the region of interior drainage of which the district to be 
described is a component part. 



THE GREAT BASIN. 

In crossing from the Atlantic to the Pacific, between the Mexican 
boundary and the central portion of Oregon, one finds a region, bounded 
by the Sierra Nevada on the west and the Rocky Mountain system on the 
east, that stands in marked contrast in nearly all its scenic features with 
the remaining portions of the United States. The traveler in this region is 
no longer surrounded by the open, grassy parks and heavily-timbered 
mountains of the Pacific slope, or by the rounded and flowing outlines 
of the forest-crowned Appalachians, and the scenery suggests naught of 
the boundless plains east of the Rocky Mountains or of the rich savannas 
of the Gulf States. He must compare it rather to the parched and desert 
areas of Arabia and the shores of the Dead Sea and the Caspian. 

To the geographer the most striking characteristic of the country 
stretching eastward from the base of the Sierra Nevada is that it is a 
region of interior drainage. For this reason it is known as the '* Great 
Basin." No streams that rise within it carry their contributions to the 



8 GEOIiOGICAL HISTORY OF LAKE LAHONTAN. 

ocean, but all the snow and rain that falls inside the rim of the basin is 
returned to the atmosphere, either by direct evaporation from the soil or 
after finding its way into some of the lakes that occupy the depressions of 
the irregular surface. The climate is dry in the extreme, the average 
yearly rainfall probably not exceeding 1 2 or 1 5 inches. 

The area thus isolated from oceanic water systems is 800 miles in length 
from north to south, and nearly 500 miles broad in the widest part, and 
contains not far from 208,500 square miles — an area nearly equal to that of 
France. The southern part of the region includes the Colorado Desert, 
Death Valley, and much of the arid country in southern California and Ne- 
vada. In northern Nevada the Carson and Black Rock deserts exhibit the 
extreme of desolation. The most northerly part of the Great Basin, occupy- 
ing the central portion of Oregon, is less barren, its rugged surface abound- 
ing in long and narrow mountain ranges, volcanic table lands, and isolated 
mesas, weathering as they grow old into rounded buttos, that are covered 
with luxuriant bunch-grass and bear a scattered growth of cedars and pines. 
At the south the valleys of the Great Basin are low-lying, Death Valley 
and the Colorado Desert being depressed below the level of the sea ; but at 
the north the valleys have a general elevation of from 4,000 to 5,000 feet, 
while the intervening mountain ranges rise from 5,000 to 7,000 feet above 
them. 

Diversifying this region are many mountain ranges and broad desert 
valleys, together with rivers, lakes, and cations, topographic elements to 
be found in all quarters of the world, but here characterized by features 
peculiar to the Great Basin The mountains exhibit a type of structure not 
described before this region was explored, but now recognized by geologists 
as the " Basin Range structure." They are long narrow ridges, usually 
bearing nearly north and south, steep upon one side, where the broken 
edges of the composing beds are exposed, but sloping on the other, with a 
gentle angle conformable to the dip of the strata. They have been formed 
by the orographic tilting of blocks that are separated by profound faults, 
and they do not exhibit the anticlinal and synclinal structures commonly 
observed in mountains, but are monoclinal instead. 



DESERTS OF THE GEEAT BASIN. 9 

The valleys or plains separating the mountain ranges, far from being 
fruitful, shady vales, with life-giving streams, are often absolute deserts, 
totally destitute of water, and treeless for many days' journey, the gray- 
green sagebrush alone giving character to the landscape. Many of them 
have play as in their lowest depressions — simple mud plains left by the evap- 
oration of former lakes — that are sometimes of vast extent. In the desert 
bordering Great Salt Lake on the west and in the Black Rock Desert of 
northern Nevada are tracts hundreds of square miles in area showing 
scarcely a trace of vegetation. In winter, portions of these areas are occu- 
pied by shallow lakes, but during the summer months they become so baked 
and hardened as scarcely to receive an impression from a horse's hoof, 
and so sun- cracked as to resemble tessellated pavements of cream colored 
marble. Other portions of the valleys become incrusted to the depth of 
several inches with alkaline salts which rise to the surface as an efflores- 
cence and give the appearance of drifting snow. The dry surface material 
of the deserts is sometimes blown about by the wind, saturating the air 
with alkaline particles, or is caught up by whirlwinds and carried to a great 
height, forming hollow columns of dust. These swaying and bending col- 
umns, often two or three thousand feet high, rising from the plains like pil- 
lars of smoke, form a characteristic feature of the deserts. 

Most of the rivers of the Great Basin have their sources in the melting 
snows of the mountains which form its eastern and western borders, and 
flow into the desert valleys within tlie rim of the undrained area. Of such 
the Bear, Weber, and Sevier rivers are examples along the eastern border; 
on the west the Truckee, Carson, and Walker rivers have a similar origin 
and destiny. A single river, the Humboldt, is anomalous in that both its 
source and its terminus are well within the area of interior drainage. 

The rivers of the Great Basin vary greatly in volume with the varying 
seasons, and some of them disappear entirely during the hot summer months 
In the streams that are perennial a high percentage of the annual discharge 
is crowded into a brief space toward the end of the rainy season. Thus 
the arteries of this parched and heated country make but one feverish pul- 
sation in a year. The streams usually diminish in volume as they descend 
into the valleys, and in many instances their waters are lost on the thirsty 



10 GEOLOmCAL HISTORY OF LAKE LAHONTAN. 

deserts and their channels run dry. In general they are larger near their 
sources than at their mouths. Commonly, too, instead of being pure, spark- 
ling waters, refreshing to the lips as well as to the eye, they are heavy with 
sediment and bitter and alkaline to the taste. 

The lakes into which much of the surface drainage finds its way are 
commonly saline and alkaline — their shores desert wastes, shunned by 
animals and by all but salt loving plants. Of the saline lakes, the typical 
example is furnished by Great Salt Lake in Utah, an inland sea whose fea- 
tures call to mind the familiar descriptions of the Dead Sea in Palestine. 
Mono Lake in California, and Abert and Summer lakes in Oregon, are 
also highly charged with saline matter, and are remarkable for the amount 
of sodium and potassium salts which they contain. Pyramid, Walker, 
Winnemucca, and Carson lakes in Nevada, as well as many smaller lakes 
throughout the Great Ba«in, are also without outlets, but yet, contrary to 
what we would expect, they hold but comparatively small percentages of 
saline matter in solution. 

Other lakes, which indicate still more pointedly the contrast between 
an arid and a humid climate, we may call playa-lakes. These are sheets of 
shallow water, covering many square miles in the winter season, but evap- 
orating to dryness during the summer, their beds becoming hard, smooth 
mud-plains or pUiyas. In many instances a lake is formed on a playa dur- 
ing a single stormy night, only to disappear beneath the next noonday sun. 
When the weather is unsettled these lakes are scarcely more permanent 
than the delusions of the mirage, but come and go with every shower that 
passes over the land. Other playa-lakes retain their integrity for a longer 
period, and only become dry during excessively arid seasons. Examples 
of these are furnished by Honey Lake in California, North Carson Lake 
("Carson and Humboldt Sink") in Nevada, and Sevier Lake in Utah, all 
of which have been known to become dry during the past few years. The 
water of playa-lakes has a greenish yellow color, due to the extremely fine 
silt which is held in suspension and not allowed to settle, because every 
breeze stirs the shallow alkaline water to the bottom. A remarkable lake of 
this class is sometimes fonnod in the northern part of the Black Rock Desert, 
in Nevada, during extremely wot seasons. Its water is furnished mainly 



LAKES OF THE GEE AT BASIN. 11 

by Quinn River, and it has been known to have a length of 50 or 60 miles, 
with a breadth of 20. During the summer it disappears entirely, leaving 
an absolutely barren plain of mud, Quinn River at the same time shrinking 
back a hundred miles towards its source. The peculiar history of playas 
and playa-lakes will be more fully described in connection with the physi- 
ography of the Lahontan basin, which is the subject of Chapter III. 

A few lakes situated on the borders of the Great Basin have outlets, 
and discharge their surj^lus waters into reservoirs at lower levels within the 
area of interior drainage. These are of the same type as the ordinary lakes 
of humid climates, with waters as pure and fresh as springs and melting 
snow can furnish. Their finest example. Lake Tahoe, lies just within the 
western rim of the Great Basin, at an elevation of 6,247 feet, amid the peaks 
of the Sierra Nevada. Its outlet, the Truckee River, flows downward with 
a descent of 2,400 feet to Pyramid and Winnemucca lakes, where the water 
is evaporated, leaving the lower lakes charged with scda salts. Just within 
the eastern border of the Great Basin lie Bear Lake and Utah Lake, the 
former discharging its waters through the Bear River and the latter through 
the Jordan River to Great Salt Lake. These streams carry down from the 
mountains their small percentages of saline matter, as a contribution to the 
already saturated solution of the inland sea where their waters are evap- 
orated. 

It may be taken as a rule that all lakes which overflow are fresh, and 
all lakes which do not find outlet become in time charged with mineral 
salts. River water is never absolutely pure, but contains a small percent- 
age of mineral matter, which is left behind when the water is evaporated. 
Should this process continue long enough it is evident that a lake without 
an outlet would in time become a saturated solution, from which the less 
soluble mineral salts would begin to crystallize. 

The examination of those inclosed lakes of the Great Basin that are 
comparatively fresh, and especially of the lakes occupying the Lahontan 
basin, shows that salt lakes may in some instances become essentially fresh 
without overflowing. It has been suggested by Mr. G. K. Gilbert, in expla- 
nation of this apparent anomaly, that a lake may evaporate to dryness and 
its salts become buried beneath the deposits of playa-lakes, so that on the 



i] 



I 



t 



I 

-i I 
I 



12 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

return of humid conditions the water that reoccupies the old basm may be 
comparatively, if not absolutely, fresh. 

To the artist the scenery of the arid lands of the Far West contrasts 
with that of more humid regions by the russet-brown desolation of the 
valleys, the brilliant colors of the naked rocks, and the sharp, angular out- 
lines of the mountains. A country without water is necessarily a desert, 
while with abundant moisture, at least in tropical and temperate latitudes, 
it becomes a garden of luxuriant vegetation. In the most desert portions 
of the Great Basin the annual precipitation does not exceed four inches, 
while in the valleys on the borders of the basin it probably reaches 20 or 
30 inches. Throughout tliis region the only fruitful areas are along the 
margins of streams, or where springs come to the surface. In such places, 
\ where water can be had for irrigation, one finds oases of delicious shade, 

with green fields and orchards yielding an unusually abundant harvest 
Thus in nearly all its physical features the Great Basin stands in marked 
contrast with those favored lands where rain is more abundant and more 
evenly distributed. 

The rainfall that a region receives is a potent though silent factor, which 
controls an almost infinite series of results in its physical history and topog- 
|!J. i raphy. In a humid region vegetation is usually luxuriant; the rock forms 

' ji ' are masked by forests, erosion is rapid, and the rocks are commonly buried 

f : beneath the accumulations of their own debris or concealed by layers of 

r[ i vegetable and animal mould that in turn are clothed with vegetation. The 

hills have flowing outlines and are dark with foliage. The valleys have 
gently sloping sides that conduct the drainage into streams meandering 
through broad plains, and the whole scene has the softness and beauty of a 
garden. In an arid land like the Great Basin all this is changed. The 
mountains are rugged and angular, usually unclothed by vegetation, and 
receive their color from the rocks of which they are composed. From the 
. gorges and cations sculptured in the mountain sides alluvial cones descend 

to the plain. These sometimes have an extent of several miles, and they 

are steep or gentle in slope according to the grade of the streams that formed • 

them. The valleys, even more dreary than the mountains, are without 

arboreal vegetation and without streams, and form a picture of desolation 

J 



] 



1 



'I' 

I- 



,1 

!• 
!. 



:Ji 



BRILLIANT COLORING OF ARID REGIONS. 13 

and solitude. In traveling through the Great Basin one sometimes rides a 
hundred miles without sight of a tree, and many times that distance without 
finding shade enough to protect him from the intense summer sun. 

The bare mountains reveal their structure almost at a glance, and show 
distinctly the many varying tints of their naked rocks. Their richness of 
color is sometimes marvelous, especially when they are composed of the 
purple trachytes, the deep-colored rhyolites, and the many-hued volcanic 
tuflFs* so common in western Nevada. Not unfrequently a range of volcanic 
mountains will exhibit as many brilliant tints as are assumed by the New 
England hills in autumn. On the desert valleys the scenery is monotonous 
in the extreme, yet has a desolate grandeur of its own, and at times, especially 
at sunrise and at sunset, great richness of color. At mid-day in summer 
the heat becomes intense, and the mirage gives strange delusive shapes to 
the landscape, and oflFers false promises of water and shade where the expe- 
rienced traveler knows there is nothing but the glaring plain. When the 
sun is high in the cloudless heavens and one is far out on the desert at a 
distance from rocks and trees, there is a lack of shadow and an absence of 
relief in the landscape that make the distance deceptive— the mountains 
appearing near at hand instead of leagues away — and cause one to fancy 
that there is no single source of light, but that the distant ranges and the 
desert surfaces are self-luminous. The glare of the noonday sun conceals 
rather than reveals the grandeur of this rugged land, but in the early morn- 
ing and the near sunset the slanting light brings out mountain range after 
mountain range in bold relief, and reveals a world of sublimity. As the 
sun sinks behind the western peaks and the shades of evening grow deeper 
and deeper on the mountains, every ravine and caiion becomes a fathomless 
abyss of purple haze, shrouding the bases of gorgeous towers and battle- 
ments that seem incrusted with a mosaic more brilliant and intricate than 
the work of the Venetian artists. As the light fades and the twilight 
deepens, the mountains lose their detail and become sharply outlined sil- 
houettes, drawn in the deepest and richest purple against a brilliant sky. 

*The word iufa is used throughout thin volume to designate deposits of calcium carbonate. 
When the volcanic product is meant, for which the same name is sometimes used, we shall designate 
it by the word %ujf. 



14 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

The succession of seasons is less plainly marked on the deserts of the 
Great Basin than on the forest-covered hills of the Atlantic slope. As 
autumn advances, but little change appears in the color of the landscape, 
excepting, perhaps, a spot here and there of gold or carmine high up on 
the mountains, where a clump of aspens or of dwarfed oaks marks the site 
of a spring that trickles down and loses itself among the rocks. The valleys 
with their scanty growth of sage remain unchanged, as do the dusky bands 
of pines and cedars on the higher mountains As the autumn passes away, 
the skies lose their intense blue, and become more soft and watery, more 
like the skies of Italy. The hues of sunset appear richer and more varied, 
and during the day cloud masses trace moving lines of shadow on the 
surface of the desert. By and by storm-clouds gather in black, gloomy 
masses that envelop the ranges from base to summit. These early storm- 
clouds cling close to the mountains and yield to the parched deserts but a 
few scattered drops of rain. The observer from below hears the raging 
tempest amid the veiled peaks, while all about him is sunshine. The 
mountains wrapped in impenetrable clouds, the glare of lightning and the 
deep roll of thunder as it echoes from cliff to cliff and from range to range, 
bring to mind the scriptural account of the storms of Sinai. And when 
the black clouds at last roll back from the mountains, and the sun with a 
wand of light dispels the storm, behold what a transfiguration! The peaks 
are no longer dark and somber, but glitter with the silvery sheen of freshly 
fallen snow. 

As winter approaches, the storms amid the uplands become mor€ 
frequent, until every range is white as snow can make it, and the tent-like 
mountains gleam like the encampment of some mighty host. Long aftev 
they are covered, the valleys between are bare as in midsummer, and the 
snow seldom lies upon them for more than a few days at a time. The 
highlands retain their snow far into summer, but on none of the ranges can 
it be said to be perpetual. In the valleys there are flowers beneath the 
sage-brush by the middle of April, but from that time until November 
scarcely a drop of rain falls. For many days and sometimes for weeks the 
skies are without a cloud. 



EARLY DISCO VEBIE8. 15 

The agriculture of this arid region is restricted to those scanty areas 
of land that can be irrigated. Of more importance is the grazing of sheep 
and cattle on the bunch-grass that frequently abounds amid the mountains 
and sometimes grows beneath the sage-brush. The mines of the precious 
metals, however, are the principal source of wealth, and to them must now 
be added a growing industry in salt, borax, sulphur, and carbonate of soda. 

The Great Basin is not attractive to the pleasure-seeker, but to the 
geologist it is peculiarly fascinating, both because the absence of vegetation 
gives such uimsual facilities for investigation, and because of the character 
of the problems to be solved. It is in this inhospitable region, now so arid 
that many a lost traveler has perished frou) thirst, that the great lake existed 
in recent geological time, which has been made a subject of study by the 
writer and his associates, the results of which are now presented. 



EXPLORATIONS. 

The existence of a great area of interior drainage on this continent, 
similar in many ways to the desert region of southern Asia, was not 
known, except to the early Spanish missionaries, among whom the name of 
Father Escalante is most prominent, and to trappers and hunters, who left 
no records of their observation, luitil Capt. B. L. E. Bonneville reached its 
eastern border in 1832.^ A year later, a party led by Joseph Walker trav- 
eled across to the Pacific coast, by way of the Humboldt River and the 
Carson Desert. This expedition returned by a more southern route, and 
determined that much of the country explored did not drain to the ocean. 

Ten years later, J. C Fremont, then a lieutenant in the Army, carried 
his bold explorations into the same region, and gave the name of " The 
Great Basin " to the rugged and arid country which he traversed westward 
of the Rocky Mountains. A comprehensive, and, for the most part, an 
accurate, description of the general features of tlie Great Basin, was pub- 
lished by Fremont in his report of 1848;^ a detailed narrative of his jour- 
neys in 1842, '43, and '44 having been published three years previously.* 

' Adventures of Captain Bonneville, by Wanhington Irving. 

•"^ Geographical Memoir upon Upper California, Washington, D. C, 1848, p. 7. 

^ExploiiDg Expedition to the Rocky Mountains. Washington, 1845. 



16 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



A summary of the results of exploration in this region previous to 1857 
was prepared by Lieut. G. K. Wan-en, and published in Volume XI of the 
Reports of the Pacific Railroad Explorations, to which we must refer the 
reader for detailed information in this connection. 

A portion of the region of interior drainage is within the boundaries of 
California, and came within the limits of the explorations of the geological 
survey of that State, carried on under the direction of Prof. J. D. Whitney. 
Volume I of the reports of that survey contains a brief account of the Great 
Basin," relating principally to its southern border, which was compiled from 
the notes of several travelers. 

Since the completion of railroad communication with the Pacific coast 
in 1869, important advances have been made in our knowledge of the Great 
Basin. The Central and Southern Pacific railroads have crossed it and sent 
numerous branches through its desert valleys, both northward and south- 
ward from the trunk lines ; many towns and mining camps have sprung up 
along these highways, and almost every foot of easily irrigable land has 
been appropriated by settlers. Herds of cattle and sheep find subsistence - 
on the mountains and in the sage-brush-covered valleys which were once 
thought to be too barren to become of service to man. Some of the most 
productive silver mines in the world have been developed in this inhospita- 
ble region. Throughout the eastern border of the Great Basin, in Idaho, 
Utah, and Arizona, the followers of the Mormon faith have found a " prom- 
ised land," which by untiring toil and industry they have reclaimed from 
its primitive desolation and made the home of thousands. With all this 
advancement, however, the Great Basin is but thinly settled, when we 
consider its vast area ; but, owing to its desert nature, probably contains a 
larger population than its agriculture alone can sustain. Together with the 
settlement of the country, exploration has gone forward until but little of 
the great terra incognita of thirty years ago remains unmapped ; scarcely 
move than a beginning has been made, however, in unravehng its compli- 
cated geological history. The United States Geological Exploration of the 
Fortieth Parallel, in charge of Clarence King, mapped the geology of a 
belt 100 miles wide across its northern portion. A large part of the Great 
*Pag«461. 



BXPLORATrON OF THE LAHONTAN BASIN. 17 

Basin was also mapped b}^ the surveys in charge of Capt. George M. Wheeler 
and Major J. W. Powell ; and geological explorations have been carried over 
large areas by the geologists connected with these surveys. The present 
Geological Survey has made special studies of a few of the principal mining 
centers of the Great Basin, and commenced the investigation of its surface 
geology in a systematic manner. Even with such a favorable beginning, 
many years of patient investigation, accompanied at times with hardships 
and privations, will be required before the geology of the Great Basin can 
be fully written. 

The exploration of the Lahontan basin, so far as is definitely recorded, 
began in 1833, when it was crossed by the party in charge of Joseph 
Walker, as previously mentioned. No report of this journey has been 
published excepting in Irving's attractive book describing the adventures of 
Captain Bonneville. In 1843, '44, '45, and '46, Fremont traversed the La- 
hontan basin throughout nearly its entire extent from north to south and 
made many geographical discoveries ; but although he noted the presence 
of tufa deposits about Pyramid Lake, and published a sketch of the tufa- 
coated island which suggested its name, he does not seem to have recog- 
nized that his route led through the desiccated bed of an ancient inland sea. 

In 1854, Capt. E. G. Beckwith*^ crossed the northern part of the Lahontan 
basin, in the region of the Black Hock and Smoke Creek deserts, but gave 
little attention to the geology of the country traversed ; the main object 
of his exploration being the discovery of a i)ractical railroad route to Cali- 
fornia. Other reports of a similar nature might be cited, as that of Capt. R. 
IngallsJ who traversed the Lahontan basin in the latitude of the Carson 
Desert in 1855; little information of geological importance is contained, 
however, in the narratives of these earlier expeditions. 

The exploring party in command of Capt. J. II. Simpson® entered the 
Lahontan basin at Sand Spring Pass, at the eastern end of Alkali Valley, in 
June, 1859, and encamped on the slough connecting North and South Car- 
son lakes ; the expedition then proceeded southward to Walker Lake, by 

•Pacific Railroad Reportn, Washington, D. C, 18()l, Vol. II. 

'Congressional Documents: 34th, Ist, H. K. Ex. Doc. 1, i>. 156. 

^Explorations Across the Great Basin of Utah, Washington, D. C, 1H70, pp. 312, 313. 

MoN. XI— 3 



18 GEOI-OOICAL HISiORY OF LAKE LAHONTAN. 

way of Allen's Springs, and afterwards traversed Mason and Carson val- 
leys, whidi, as we now know, were alao occupied by the waters of Lake 
Laliontan. Tlie presence of ancient water lines and of calcareous tufa 
deposits about the borders of the Carson Desert "wnn recorded by Henry 
Engelmann, the geologist of the expedition, in liis report on the geology 
of the country traversed during the reconnaissance, but time did not per- 
mit an extended study of the surface geology of the region. That lai-g© 
portions of the area of interior drainage had at no distant time been 
occupied by lakes was clearly recognized, and the cause of their disappear- 
ance was correctly ascribed to climatic changes. 

During the progress of the United States Geographical Surveys west 
of the 100th Meiidian, in charge of Capt. George M. Wheeler, large por- 
tions of the Lahontan basin were topographically surveyed, but no report 
on the geography oi- geology of the region has been published. 'I'he maps 
prepared by this survey, and also those issued in connection with the 
exploration of the Fortieth Parallel, were exceedingly useful during the 
field work of the present investigation, and were freely used in compiling 
the pocket map accontpanying this report, as well as in preparing some of 
the smaller illustrations. 

The exploration of the Fortieth Parallel included a belt 100 miles 
wide which crossed tlie Lahontan basin, but left considerable areas both 
to the north and south unmapped. In the reports of that survey Lake 
Lahontan received its name, and it is discussed to considerable length 
by the geologist in charge (Vol. I). Many detailed observations relating 
to the history of the former lake were recorded Ijy Messrs. Arnold Hague 
and S. F. P^mmons as a part of their report (Vol. II) of field observations. 
It is not necessary to introduce an abstract of the results reached by these 
geologists in reference to the history of the former lake, as we shall have 
frequent occasion to refer to their work in the pages that follow. 

In 1872 Dr. James Blake made a journey from Winnemucca, Nevada, 
to tlie Pneblo Mountains, Oregon, during which he traversed the northern 
portion of the Lahontan basin, and made man}' observations in reference 
to tufa deposits, teiraces, fossil shells, etc. The results of these observa- 
tions were published in two brief papers in Vol, IV (1872) of the Proceedings 



WOEK OF THE PRESENT SURVEY. 19 

of the California Academy of Sciences.® In these papers the possibility of an 
outlet to the ocean for the waters of the Great Basin during the Quaternary 
is suggested, and nieasurenients are given of the altitude of some of the 
passes in the northern part of Nevada which lead towards the drainage 
of the Columbia. That the passes in this region could not have furnished 
a point of discharge for Lake Lahontan will be shown in the following 
chapter (page 34). 

The study of the surface geology of the Great Basin, undertaken by the 
United States Geological Survey, was begun in the summer of 1880; a 
section of the survey, entitled the *' Division of the Great Basin,'' having 
previously been organized under the leadership of Mr. G. K. Gilbert, with 
headquarters at Salt Lake City, Utah. The first field season was occupied 
with the study of Lake Bonneville, the results of which have been pub- 
lished by Mr. Gilbert in a somewhat popular essay in the second annual 
report of the survey; the final report, in the form of an independent mono- 
graph, is now in preparation. 

In April, 1881, the writer commenced a geological reconnaissance 
through the northern part of the Great Basin, during which the northern 
half of Nevada was crossed and recrossed, and excurf^ions were made into 
eastern California and southern Oregon. As the firet year's exploration 
was entirely of a preliminary character, without scientific assistants, all 
detailed study and instrumental work was deferred until the following 
season. The reconnaissance of 1881 occupied seven months, during which 
about 3,500 miles were traversed in the saddle, the route being planned 
with special reference to the study of Quaternary geology. During the 
season the basin of Lake Lahontan was crossed in various directions and 
much of its history was deciphered. A sketch of the geology of Lake 
Lahontan, so far as determined from the first season's explorations, was pub- 
lished in the Third Annual Report of the United States Geological Survey. 

While carrying forward the reconnaissance of 1881, the Mono basin, 
California, was visited and the study of its geological history begun; this 
task was left unfinished, however, until the region could be topograph- 

'Oo the absence of a rim to the Great Basin to the west of Pueblo Bntte, p. 223. Remarks on the 
Topography of the Great Basin, pp. 270-27y. 



20 GKOLOGI0z\L HISTORY OF LAKE LAHONTAN. 

ically surveyed. From the experience gained during the first season's 
work, a plan of investigation was developed which was carried out during 
the summers of 1882 and 1883. 

On taking the field at Winnemucca, Nevada, in the spring of 1882, I 
was joined by Mr. Willard D. Johnson, of Washington, D. C, who accom- 
panied me on a journey through that portion of the Great Basin that lies 
north of the hydrographic rim of Lake l^ahontan and is situated mostly in 
Oregon. The results of this exploration, so far as the surface geology of 
the region is concerned, were published in the Fourth Annual Report of the 
United States Geological survey. During this reconnaissance the pre- 
vious conclusion that I^ake Lahont^m did not overflow northward was fully 
confirmed. The Great Basin north of the Nevada-Oregon boundary, in 
common with the main area of interior drainage, is divided into a number 
of independent hydrographic basins, many of which held Quaternary lakes 
that must have been contemporaneous with the great lakes of Utah and 
Nevada 

On returning to Winnennicca in July, 1 was joined by Mr. W J McGee 
as geological aid, and a few weeks later by Mr. George M. Wright, also in 
the same capacity. Proceeding southward from Winnemucca we examined 
the Lahontan sediments, terraces, tufa deposits, etc., occurring in the Hum- 
boldt Valley, and then continued our journey southward in order to study 
the region about Humbolt, Pyramid, Winnemucca, and Walker lakes. 
Later in the season we entered the Mono Lake basin and began a detailed 
investigation of its Quaternary geology. Owing to the advance of winter 
we were obliged to leave the completion of this work until another season. 

During the time that the expeditions mentioned above were being car- 
ried forward, Mr. A. L. Webster, assisted by Mr. Eugene Ricksecker, was 
engaged in making a topographical survey of the northeast portion of the 
Lahontan basin, in order to complete the compilation of the accompany 
ing pocket map. The region surveyed by Mr. Webster embraced about 
8,464 square miles, and is indicated on Plate II ; the extreme eastern limit 
of the area surveyed is a few miles to the eastward of the right-hand bor- 
der of the plate. 



I : 



li 



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II 



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EXPLORATION OF THE MONO BASIN. 2l 

The various routes followed by myself and my scientific assistants 
during the exploration of Lake Lahontan are shown on Plate II, and will 
serve to indicate the degree of completeness to which we were enabled to 
carry our observations. A portion of the field season was devoted by Mr. 
Johnson to the preparation of local maps, the positions of which are also 
indicated on map forming Plate 11. 

The winter of 1882-83 was passed at the survey oflBce in Salt Lake 
City, in the preparation of notes and maps for publication, chemical studies 
connected with our work, etc. In July, 1883, I again took the field in 
company with Mr. Johnson, and recommenced work in the Mono basin. 
After devoting all the time practi(*able to the study of the Quaternary 
geology of that region I journeyed northward and passed through a large 
portion of the Lahontan basin, en route to Red Bluff*, California, where I 
disbanded my party in October. In traversing the Lahontan basin I visited 
several points of interest in the Walker River canon, about Pyramid and 
Winiiemucca lakes, and on the Black Rock and Smoke Creek deserts, thus 
being able to review many previous observations. 

Mr. Johnson completed his topographical survey of the Mono basin 
late in December, and brought to a (*,lose, at least for the ])resent, the field 
study of the Quaternary geology of the region from which the Division of 
the Great Basin derived its name 

The explorations conducted by the writer have embraced three field 
seasons, a part of each having been devoted to the study of Lake Lahontan. 
The observations made during these several journeys, so far as they relate 
to the great Quaternary lake of northwestern Nevada, are included in the 
present report. 

( )ur work in the Mono basin during tlie same years that the explora- 
tion of Lake Lahontan was Ix^ng carried forward includes a study of the 
existing lake and of the ancient lake of much greater extent that formerly 
occu[)ied the same valley ; also, the relations of both the ancient aijd the 
modern lake to the glacial and volcanic phenomena displayed on a grand 
scale in the same basin. The results of these studies will be published 
in the Sixth Annual Report of the United States Geological Survey. 



22 GEOLOGICAL HISTORY OF LAKE LAUONTAN. 

Incident to our geological studies in the Mono basin was a visit to the 
glaciers now existing amid the lofty peaks of the Sierra Nevada, on its 
western border. A sketch of the observations relating to these glaciers, 
together with a summary of what has been published in reference to these 
and other glaciers of the United States, was issued in the Fifth Annual Report 
of the United States Geological Survey. 



CHAPTER II. 

GENESIS OV LAKE LAHONTAN. 

THE FORMATION OF LACUSTRAL BASINS. 

The discussion of the origin of lake basins has been carried on with 
so much zeal during the past fifteen or twenty years that we now possess a 
large amount of literature bearing on the subject From the facts gathered 
by many observers, in widely separated localities, it is evident that the de- 
])ression8 holding lakes are extremely diverse in character and have resulted 
from many causes. In some instances lakes are held in basins produced by 
orographic movement, i. <?., by the unequal folding of rocks, by dislocation 
due to faulting, etc. Others are the result of erosion, and have for their 
typical example a rock-basin produced by glacial action. Again, there is a 
third great group of basins produced by the damming of pre-existing water- 
ways; as, for example, when the drainage of a valley is obstructed by 
moraines, land-slides, lava-flows, alluvial deposits, etc. 

Following the schedule prepared by Davis, ^^ we have three broad 
classes of lake basins : 

a. Constructive or orographic basins. 

b. Destructive or erosion basins. 

c. Obstructive, barrier, or inclosure basins. 

Each of these generic divisions is abundantly illustrated in the Great 
Basin. Very large portions, if not the entire area of interior drainage, have 

^^Claasificatiou of Lake Basins, by W. M. Davis: Proceedings of the Boston Society of Natural 
History, Vol. XXI, 1882, p. 321. 

23 



24 GEOLOGICAL HISTORY OF LAKE LAHONTAK 

been broken by a vast network of fractures accompanied by a tilting of the 
included blocks, which have given origin to orographic basins on a grand 
scale. On the borders of the region, in the glaciated valleys of the Sierra 
Nevada and Wasatch mountains, rock basins due directly to the erosion of 
glaciers may be counted by hundreds if not by thousands. From almost 
any of the peaks of the High Sierra more than a score of lakes of this char- 
acter may be observed. Lakes occupying barrier basins are also numerous 
in the canons of the Cordilleras where ancient moraines obstruct the drain- 
age. A number of the Sierra Nevada lakes which owe their origin to ero- 
sion and decomposition, resulting mainly from glacial action, will be de- 
scribed in connection with the Quaternary history of the Mono basin in 
the Sixth Annual Report of the United States Geological Survey. At pres- 
ent we are constrained to confine our attention to the more central portion 
of the Great Basin The area formerly occupied by glaciers in this region 
is very limited, and as flowing ice has been the principal agent in the for- 
mation of basins of erosion, this type of lake-basin is wanting, except about 
the summits of some of the highest of the basin ranges. Barrier basins, 
produced by the deposition of the current-borne drhris of ancient lakes in 
such a manner as to obstruct the drainage of valleys, are not uncommon in 
the interior portion of the Great Basin, but the depressions characteristic of 
the region are due to other causes. 



ORIGIN OF THE LAPIONTAN BASIN. 

The more pronounced topographic^ features of tfie Great Basin have 
been found to be the result of orographic displacement. The typical 
mountain structure of the region is monoclinal ; the elements being oro- 
graphic blocks bounded by faults, and so tilted that their upturned edges 
form mountain crests with a steep descent on one side and a more gentle 
slope in the opposite direction. The upheaved edges of faulted blocks 
usually appear as long and narrow ranges. Their depressed borders under- 



GBEAT BASIN STBUOTUBE. 25 

lie valleys. An ideal cross-section of the mountains and valleys of the 
Great Basin is shown in the following diagram: 




/ 



Flo. 1. — ^Ideal section illaHtrating Great Baain structure. 

The structure here illustrated has been found so typical of the region 
between the Sierra Nevada and the Rocky Mountains, that it has been 
named by Gilbert the "Great Basin system" of mountain structure.^^ 

The grandest displacements of the Great Basin are those determining 
its eastern and western borders, i e., the Wasatch and the Sierra Nevada 
fault?. The first has been described by King, Gilbert, and others, and has 
been traced by the writer continuously for ihore than 150 miles; the second 
has been studied at intervals for over 200 miles without determining its full 
extent. The Sieira Nevada fault is much less regular in its course, and is 
more complex than the corresponding displacement along the eastern border 
of the Great Basin. It is conspicuous in Honey Lake Valley, California, 
where its scai-p forms a line of rugged cliffs, bordering the plain on the 
west; and again along the west side of Eagle and Carson valleys, from near 
Carson City southward for fifty miles or more. In the valley of Mono 
Lake it is strongly pronounced; farther southward, in Owen's Valley, it has 
again been recognized, but its southern, like its northern terminus, is at 
present unknown. The details of this profound fracture are far from being 
understood, as it branches and changes its course in an extremely irregular 
manner. Disregarding all minor displacements, as well as the results of 
erosion and sedimenttition, we may consider the Sierra Nevada in a general 
way as the upraised edge of an orographic block, having its eastern border 
determined by the great fault we have noticed above. The desert region 
stretching eastward from the base of the mountains is the thrown side of 
the same displacement. It is on the depressed side of this fault that the 
Lahontan basin is situated. 



"U. S. Geographical Surve.vs West of the 100th Meridian. Vol. Ill, p. 21. 



26 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

It is not to be understood, however, that the old lake basin was formed 
l)y a single, simple displacement; on the contrary, it is the result of exceed- 
ingly complex faulting that affected the entire region included between the 
Wasatch and the Sierra Nevadamountains. The time when these movements 
began is unknown, but they antedate the Quaternary, were in process during 
the existence of lakes Bonneville and Lahontan, and probably have not yet 
ceased, as will be shown in Chapter X. The old lake basin, instead of 
being a simple orographic valley, is composed of a large number of separate 
and independent depressions of the Great Basin type, which are united with 
one another directly, or by the intervention of narrow passes, and so 
nearly coincident in level that a single lake 900 feet deep in the lowest 
depression could flood them all. It is to the union of these various, inde- 
pendent, monoclinal valleys that the extremely irregular outline of Lake 
Lahontan is due. 

Nearly all the ranges of northwestern Nevada are rugged and form 
serrate crests having an approximately north and south trend, and, as 
already stated, as a nearly universal rule they are monoclinal. An older 
structure, however, as first recognized by King, ^^ is frequently apparent, in 
which a folding of the rocks into anticlinal and synclinal may be traced. 
In the older deformation the rocks were crumpled and contorted as in the 
Alleghanies and the Alps, but during the later disturbances they were broken 
without being folded. The monoclinal blocks resulting from the second 
disturbance are the elements {giving character to the present topography; 
the surface features due to the former structure having been rendered 
inconspicuous by the later movements. The trend of the. fault lines, and 
consequently of the mountain axes, is in general nearly north and south, 
but in the central part of the Great Basin, north of latitude 37°, it is more 
nearly north-northeast and south-southwest. 

At present we can only call attention to a few characteristic examples 
of the displacements that gave origin to the Lahontan basin; these may be 
taken as types of the prevailing structure of the region. 

In the Santa Rosa Mountains, hi northern Nevada, the fault determining 
the trend of the range follows its western base and has a throw of not less 



'«U. 8. Geological Exploration of the Fortieth Parallel, Vol. I, p. 735. 



FAULT BASINS. 27 

than 5,000 or 6,000 feet. The eastern slope is comparatively gentle, and 
conforms in a general way with the inclination of the beds of volcanic rock 
composing a large part of the mountains. The bold western mountain face 
is in reality an eroded fault scarp; the thrown block underlies Quinn River 
Valley. 

In the case of the Jackson Range the principal fault follows its western 
base; the eastern base of the Pine Poorest Mountains is also a precipitous 
fault scarp; the Black Rock Desert, intervening between these ranges, is a 
depressed ai-ea, which has been deeply buried beneath the sediments of 
Lake Lahontan. An ideal section from east to west, through these ranges, 
is shown in the following diagram: 




FiQ. 2— Ideal section ihrongh the Black Kock Desert, Nevada. 

Tlie Pahute Range, on the eastern border of the Carson Desert, has a 
well defined line of displacement along both the eastern and the western 
base, as indicated in the followinjiif g-enerah'zed section : 








Fio. 8.— Ideal aectioa of the Pahtit« Hauf^e, Nevada. 

Great faults may also be traced along the western bases of the West 
Humboldt and Star Peak ranges. The eastern shores of both Pyramid and 
Winnemucca lakes are likewise determined by fault scarps, as indicated 
below. 

Fio. 4.— Ideal section through Pyramid and Winnemncca lakes, Nevada. 

In Walker Lake Valley the orographic structure so typical of the Great 
Basin is again repeated ; the main displacement in this instance follows the 
western border of the valley and determines the abrupt eastern face of the 
Wassuck Mountains. The topography of the valley is well shown on 
Plate XV. 




28 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

If desirable, illustrations of Basin Range structure might be multiplied, 
almost without number, not only in the Labontan basin, but throughout 
Nevada, Utah, and Arizona, and in parts of Oregon and California. On the 
accompanying map, Plate III, an attempt is made to represent the course 
of the faults that determined the main features in the present topography 
of the Lahontan basin. The data for completing a map of this nature, 
however, so as to present an accurate outline of the orography of the region, 
have not been obtained, for the reason that special attention has not been 
directed to the subject The lines of displacement that are shown have 
been sketched from actual observation, and serve, at least in the absence 
of more complete data, to indicate the vastness of the system of fractures 
that have given diversity to the topography of the region. Could every 
fault be indicated the map would be covered by an irregular network of 
intersecting lines. 

The depression formerly occupied by Lake Lahontan may be taken as 
the type of a compound rock-basin due to displacement, many of the minor 
valleys of which it is composed being examples of fault-basins of the simplest 
kind 



GEOGRAPHICAL EXTENT. 



THE HYDUOORAPHIC BASIN. 



During the Quaternary period, as at the present time, the region of 
interior draina«fe between the Sierra Nevada and the Wasatch mountains 
was divided into a large number of interior drainage areas or hydrographic 
basins, two of which were of large size, and have claimed special attention. 
These are included between the 38th and 42d parallels of latitude, and 
together occupy the entire breadth of the Great Basin. The one to the 
eastward embraced northern and western Utah, together with small portions 
of Idaho and Wyoming, and delivered its drainage to Lake Bonneville. 
The hydrographic area to the westward included the northwestern part of 
Nevada, together with small portions of California and Oregon, and dis- 
charged into Lake Lalionfcin. Lake Bonneville received the drainage from 



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PRE - QUATT-IRNARY KAULT LINES. 



QUATERNARY DRAINAGE. 29 

a surface 52,000 square miles in extent; Lake Lahontan's hydrographic 
basin embraced 40,775 square miles. 

The Bonneville basin has its lowest depression along its eastern border, 
now occupied by Great Salt Lake ; and its form was largely determined by 
the Wasatch fault. In the Lahontan area the lowest depression is situated 
near the base of the Sierra Nevada, and the topography of the basin is de- 
termined, to a considerable extent, by the fault which follows the eastern 
base of that range. 

The Bonneville and Lahontan drainage areas had a common divide for 
about 2') miles, between the 4 1st and 42d parallels, and a little east of the 
115th meridian. Southward of the 41st parallel the boundaries of the two 
great hydrographic areas diverge, the included space being divided by short 
mountain ranges into a number of independent bashis, some of which held 
Quaternary lakes of considerable size. 

The direction of the streams in the northern part of the Great Basin 
shows that the area is divided by a central axis, irregular in its trend, from 
which the surface has a general slope, both eastward and westward, to the 
bases of the inclosing mountains. 

From the Bonneville-Lahontan divide, north of Toano, the Humboldt 
River flows westward through a narrow and rugged valley which crosses 
the structural features ol' the country nearly at right angles. The course 
of the river seems to have been determined in Tertiary times, or perhaps 
earlier. During the Quaternary the LTpper Humboldt Valley was occupied 
by a stream larger than the present, which emptied into Lake Lahontan a 
few miles east of the present site of Golconda. Before reaching the lake, 
the Quaternary river received considerable additions from the north through 
the channels of the North Fork, Maggi, Rock, and Rabbit creeks, and the 
Little Humboldt River. Its most important tributary, however, in ancient 
as in modern times, came from the southward, and flowed through the nar- 
row Reese River Valley. 

On the north the Lahontan drainage area was bordered by the rim of 
the Great Basin, and by a number of small and independent areas of inte- 
rior drainage, situated mostly in Oregon and in the northwestern corner of 
Nevada. On the west tlie divide coincided for not less than 260 miles with 



30 GEOLOGICAL HISTORY OF LAKE LAHONTAX. 

the western rim of the Great Basin, and was determined by the ci-est line 
of the Sierra Nevada, from the eastern slope of which the lake received its 
greatest tribute. The Walker, Carson, and Trnckee rivers gathered the 
surface drainage of the mountains into previously excavated channels, which 
bear witness to a long period of erosion antecedent to the existence of the 
Quaternary lake. The divide between the waters that flowed into Lake 
Lahontan and the drainage of the interior basins bordering it on the south 
and east is extremely irregular, but is well defined throughout the greater 
part of its course by the crests of rugged mountains. 

The separate drainage systems into which the basin is divided are the 
Humboldt and Reese river valleys of the east, Quinn River on the north, 
the Walker, Carson, and Truckee rivers, together with Smoke and Bufiklo 
creeks, and Snowstorm and High- Rock canons on the west. The boundary 
of the region that drained into Lake Lahontan is shown on Plate IV. 
Besides the areas draining into living streams there are several desert basins 
within the Lahontan area, as represented on Plate XXIX. 

One of the most important conclusions to be derived from a study of 
the drainage in the region of Lake Lahontan during the Quaternary period 
is that the country at that time had about its present topographic form. 
The mountains were then the same as we find to-day, excepting that the 
lines carved by subaerial erosions are a little deeper, the alluvial cones 
about their bases are slightly larger, and the}' have undergone very mod- 
erate post-Quaternary orographic movements. The caflons occupied by 
the tributaries of Lake Lahontan still aflFord drainage channels when there 
is sufficient precipitation to form streams. If Quaternary man could revisit 
his jmcient hunting grounds, he would have no difficulty in recognizing the 
landmarks that were oncc^ familiar to him. Th(* mountains and valleys are 
the same, although their scanty vegetation has probably undergone many 
changes. The great lakes which were familiar to him, however, have passed 
away and given place to broad silent plains of desolation. The former 
rivers have shrunken, and many of their channels are dry. 



J S GEOLOGICAL SVRVt: 




THE liAKE BASIN. 

As may be learned from the accompanying map, Plate IV, the outline 
of the hydrographic basin of Lake Lahontan is distinguished by great 
irregularity, and no less unsymmetrical is the contour line within, that 
marks the boundaries of the former lake. As nearly as can be estimated, 
the total area of Lake Lahontan, as previously stated, was about 8,422 
square miles. Its northern extremity in Quinn River Valley reached a few 
miles north of the Nevada-Oregon boundary, and its extension southward 
was limited by the divide at the southern end of Walker Lake Valley. 
The distance between these points gives the extreme length of the lake as 
250 miles. Its eastern limit was in Humboldt Valle}^, where the river passes 
through the Sonoma Range, a few^ miles to the eastward of Golconda; and 
the most westerly point near Susanville, in Honey Lake Valley, California. 
The axis joining these two extremes is 180 miles in length. 

The area inclosed by the Lahontan beach is traversed by many 
mountain ranges, which formed peninsulas and islands during the existence 
of the lake, and divided its surface into a number of irregular water bodies 
that were connected by narrow channels. The principal water surfaces 
were grouped in two rudely parallel series, which were united at their 
northern and southern extremities by naiTOW straits. The area thus 
inclosed formed a large and extremely irregular island that bristled with 
barren and rugged mountain ranges. For convenience in description, we 
shall call the two main divisions of Lake Lahontan the Eastern and Western 
water bodies. The K astern Body covered the Carson Desert, together with 
Buffalo, Alkali, and Churchill valleys, which open from it, extended up 
Humboldt Valley to beyond Golconda, and occupied the southern part of 
the Little Humboldt Valley. From the Humboldt the lake spread west- 
ward of the Eugene Mountains and the Slumbering Hills, and entirely filled 
Quinn River Valley. 

The Western Body comprised the areas now known as the Black Rock 
and Smoke Creek deserts, together with the valleys of Honey, Pyramid, and 
Winnemucca lakes. At the north the connection between these two main 
divisions was by a naiTOW strait now traversed by the lower part of Quinn 

31 



32 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

River. Tlie water in this clianiiel during the highest stage of Lake Lahontan 
was 350 to 380 feet deej). The equally narrow strait connecting theKast 
and West bodies at the south is now occupied by the lower portion of the 
Truckee Eiver in its course between Wadsworth and Pyramid Lake. 

On Plate V, the depth of the water during the highest stage of Lake 
Lahontan is given in feet. These determinations are mostly from aneroid 
measurements, and show the lake to have been about 500 feet deep over 
the Carson Desert, becoming shallow in its extension up the Humboldt 
Valley. On the Black Rock and Smoke Creek deserts the depth was from 
500 to 524 feet. The deepest sounding in the old lake, however, as already 
stated, was at the present site of Pyramid Lake, where the depth was 886 
feet. 

While the various valleys composing the basin of Lake Lahontan are 
orographic in their character, the cafions of inflowing streams are largely 
due to erosion. All the rivers, as well as the smaller creeks that were 
tributary to the lake, flowed in deeply cut cafions, many of which were 
occupied for a long distance by the waters of the lake when it reached its 
maximum extent. These cafions will be more fully noticed in connection 
with the description of the Lahontan lake beds. 

Lahontan was intermediate in area between T^ake Erie and Lake 
( )ntario, but was far less systematic in outline than either; in fact its 
boundaries were more iiregular than any other lake, recent or fossil, that 
has been explored. As shown on the frontispiece, it was smaller than Lake 
Bonneville, and ranks as second in size of the Quaternary lakes of the Great 
Basin. 



QUESTION OF OUTLET. 

In studying the records of an ancient lake, one of the first questions to 
which it is desirable to find an answer is whether it oveiflowed or not; and 
if it did find an outlet, what are the characteristics oi the channel of dis- 
charge. The importance of determining the nature of the channel of overflow 
of a fossil lake is illustrated in the case of Lake Bonneville, which, as is well 
known from Mr. Gilbert's investigations, rose until it oveiflowed at Red-Rock 






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UKPTH OF I^Kt: I.AHONTAN AT lirCHKST WATKK STAGi: . 



ABSENCE OF AN OUTLET. 33 

Pass, in Idaho, and then cut down its outlet to the depth of 370 feet. The 
level of the first point of discharge determined the horizon of the highest 
of the Bonneville terraces. The bottom of the gorge cut by the overflowing 
stream determined the level of the Provo Beach, the most strongly accented 
of all the Bonneville water lines. 

As previous writers on Lake Lahontan have conjectured that there was 
an outlet at its southern end^^ this was the first portion to be explored when 
the present study was undertaken. On examining Gabb's Valley, it was 
found that a mountain barrier intervened between it and the Lahontan 
basin to the northwest, thus proving that it was not occupied by that lake, 
and, moreover, was not included in its hydrographic basin. From the 
southern end of the Carson Desert a long narrow arm of the former lake 
extended into the desert valley which opens southward from Allen's Springs. 
The southern end of this valley is low and filled with alluvium which has 
been formed into gravel bars by the waters of Lake Lahontan; these sweep 
about the end of the basin in graceful curves, the highest in the series 
coinciding with the horizon of the highest water level of Lake Lahontan, 
thus proving conclusively that the lake did not here find an outlet. 

The highest of the Lahontan beaches at the eastern end of Alkali Val- 
ley is far below the lowest part of Sand Spring Pass, which proves that La- 
hontan did not enter Fairview Valley through this gap. 

The Lahontan beach may be traced with ease along the steep vol- 
canic bluff's bordering the Carson Desert on the south, from Allen's Spring, 
to where the Carson River breaks through the range. The lake extended 
through the Carson River cafion and occupied Churchill Valley and the 
valley of the Carson River as far as Dayton. Opposite Old Camp Churchill 
there is a narrow gap in the hills bordering the valley on the south, which 
at first gives promise of having been an outlet of the ancient lake. On fol- 
lowing up this valley we find it ascending with a low grade and opening 
through a narrow gap into Mason Valley, about which there are beach 
lines, showing that it too was once filled by a lake. The highest beach in 
Mason Valley is on a level with the top of a narrow divide which has been 

»3King: U. S. Geological Exploration of the Fortieth Parallel, Vol. I, p. 507. Whitney: Cli- 
luatic Changes in Later Geological Time, p. 110. Memoirs of the MuHeun; of Comparative Zoology of 
Harvard College, Vol. VII. No. 2. 

MnlJ. XI— ^ 



34 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

cut through by a stream that once flowed into Lahontan basin through the 
channel that opens opposite Old Camp Churchill. The lake which occu- 
pied Mason and Walker Lake valleys cut down its point of overflow about 
85 feet, and discharged its waters northward. The bottom of the channel, 
thus formed, where it leaves Mason Valley is between 60 and 70 feet below 
the level of the Lahontan beach, as determined by measurements of level 
connected with the profile of the Carson and Colorado Railroad. These 
measurements indicate that Lake Lahontan did not extend into Mason 
Valley until after the channel cut by the overflow from that basin was 
formed. We know, however, that there has been considerable post- 
Lahontan orographic movement in this region, and it seems not unlikely 
that the relative height of Mason Valley and the Lahontan beach along 
the Carson River, may have been changed since the evaporation of the 
former lake. It is, therefore, possible that Lahontan during its highest 
stage extended through the pass connecting Churchill and Mason valle^-s, 
before the present channel was excavated, and occupied Mason and Walker 
Lake valleys. The tufa deposits about Walker Lake, as will be explained 
in a future chapter, are of the same nature as the similar formations in the 
main areas of Lake Lahontan, and indicate that they were precipitated 
from waters of the same character. 

After determining that Lake Lahontan did occupy Walker Lake 
Valley, we explored its ancient beaches, and found that the former lake 
extended only a few miles southward of the one which now fills the bottom 
of the basin. Well preserved gravel bars sweep around the southern end 
of the valley but do not reacli the level of the pass leading south into Soda 
Springs Valley; at the end of this basin there is also a low pass that is 
uncut bv stream erosion. 

As the localities noticed above are the only ones on the southern 
border of tlie Lahontan basin that would suggest a possible outlet, the con- 
clusion that the former lake did not overflow in that direction is positive. 

In the northern part of the basin all the passes leading to the valleys 
draining into the Owyhee, one of the tributaries of the Columbia, were 
specially examined, as well as the divide between the northern end of the 
Black Rock Desert and Alvord Valley; at none of these phices are there 



ABSENCE OF AN OUTLET. 35 

channels of overflow. The divide at the northern end of the Black Rock 
Desert was the lowest point on the northern rim of the basin, but it was at 
least 200 feet above the Lahontan beach near at hand; moreover, the rim 
of the basin at this point was never cut by a transverse channel of erosion. 
This point was visited by Dr. James Blake in 1872, who determined its 
elevation to be "590 feet above the valley of Queen's [Quinn] River at 
the place where it makes a bend to the southwest, to lose itself in the 
Black Rock Desert,"^* Lake Lahontan at the point in Quinn River Valley 
designated by Dr. Blake, was 380 feet deep, thus furnishing additional 
evidence that the ancient lake did not attain the level of the pass in 
question. 

During the topographic survey of the northern portion of the Lahon- 
tan basin the highest water line of the old lake was mapped with care and 
found continuous throughout. The lake extended into King River Valley 
which formed a complete cul de sac, with no opening except into the Black 
Rock Desert. At the head of Quinn River the bottom of the valley slopes 
upward until at the divide it is several hundred feet above the horizon of 
the Lahontan beach. The northern border of Paradise Valley was closely 
examined by Mr. Webster, and gave positive evidence that it was not 
a point of discharge for the old lake. During the progress of our work 
every point on the northern rim of the basin that could be suspected of 
having been low enough to allow the old lake to overflow was examined 
either by the writer or his scientific assistants, and found to be unbroken 
by a channel of discharge such as an overflowing lake must necessarily 
excavate. 

It is important to keep in mind the absence of an outlet while reading 
Lahontan history, as it has a direct bearing on the character of the shore 
topography which records the extent of the lake at various stages, and 
furnishes the key to the chemical history of the waters which formerly^ 
flooded the basin. 



" Proceedings of California Academy of Sciences, Vol. IV, 1872, p. 276. 



. I . 




MAI' SIIOVVINC, I„\M> <I.AS.sn'ICAIION Ol-' TiM': I.AHUNTAN KKCION 



DESERTS OF THE LAHONTAN REGION. 37 

Carson Desert, so situated as to be conveniently watered from the Carson 
River, are also under irrigation. At a limited number of localities on the 
borders of the Black Jiock Desert and in Quinn River Valley the water from 
springs and small mountain streams is used to irrigate gardens or a few acres 
of grain. In Mason and Honey Lake valleys there are swampy meadows 
of considerable extent adjoining irrigable lands where abundant harvests 
are annually secured. 

The Central Pacific Railroad passes for l(i5 miles through the desic- 
cated bed of the extinct lake, entering it a few miles east of Golconda and 
leaving it, on the west, in the Truckee Canon about 15 miles west of Wads- 
worth. Nearly all the villages in the basin are located along this highway, 
which furnishes supplies for a wide extent of country. The traveler in 
crossing western Nevada by rail for the first time will perhaps be impressed 
with its barren nature and perhaps conclude that it is unfit for human hab- 
itation. With the exception of Mason and Honey Lake valleys, however, 
it is the most fruitful portion of the Lahont^n basin. A typical example of 
the deserts of Nevada may be seen from the track of the Central Pacific 
Railroad between Humboldt Lake and the Truckee River, including a 
glimpse of the Carson Desert to the southward of Humboldt Lake, which 
was once covered by 500 feet of water. 

The Carson and Colorado Railroad also passes through a portion of the- 
basin once occupied by Lake Lahontan. On going south from Dayton the 
traveler by this route follows a narrow valley formed in part by the ero- 
sion of the Carson River, and subsequently occupied by Lake Lahontan. 
Opposite the site of Camp Churchill the road bends abruptly southward and 
traverses a narrow pass leading to Mason Valley; from there it follows 
Walker River and the eastern shore of Walker Lake and crosses the south- 
ern extremity of the old lake margin at a point a short distance south of 
Hawthorn. Throughout this entire distance, with the exception of a short 
space in the Walker River Canon, the road is below the level of the highest 
beach of the old lake. 



38 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

MOUNTAINS. 

The numerous narrow and rugged mountain ranges of the Lahontan 
basin, excepting in a few instances where they are scantily clothed with 
cedars and pine, are nearly as barren and desolate as the intervening sage- 
brush valleys. The Sierra Nevada, as is well known, supports varied and 
beautiful coniferous forests that are valuable for the timber and wood which 
they supply. The trees are mainly confined to the moderately elevated 
portions of the range, their upper limit or the " timber line" having an ele- 
vation of about 10,000 feet. The lower extent of arborescent vegetation, 
more especially of the pines, is apparently determined by lack of moisture, 
and along the eastern base of the Sierra Nevada occurs at an elevation of 
about 5,000 feet. The upper limit of timber-growth is invariably occupied 
by pines, which, owing to the severe winter climate of the elevated regions, 
are dwarfed and gnarled, and, at their extreme upper limit, extended prone 
on the mountain side. At widely separated points in the High Sierra, where 
exposed to the full fury of the winter storms, the branches and trunks of the 
pines are stripped bare of leaves and bark, and even eroded by the drifting 
ice-crystals to a considerable depth, thus recording a recent climatic change 
that has produced more severe storms than were experienced during the 
earlier history of the trees. King states that this recent climatic oscil- 
lation began previous to 1870, and was the first of its kind for over 250 
vears.'^ 

In the northern part of the Lahontan basin the most conspicuous ranges 
are the Santa Rosa, Jackson, and Pine Forest. The first two of these are 
scantily clothed with cedars, above which rise the bare and rugged mount- 
ain crests; the third, on the western border of the northern extension of 
the Black Rock Desert, is covered over a limited area with a forest of yel- 
low pine, from which the range derives its name. The mountains bordering 
on the Carson Desert on the east are dark with piiion, and afford to the 
Pahute Indians an abundant harvest of pine-nuts during certain seasons. 
On the precipitous mountains overshadowing Walker Lake on the west, 
there is a timber band, composed almost entirely of pinon, commencing 
about 1,000 or 1,500 feet above the lake, and extending upwards to within 

^^{J. S. Geological Exploration of the Fortieth Parallel, Vol. I, p. 527. 



MOUNTAIKS OF THE LAHONTAN liEGION. 39 

1,000 feet of the highest summits. When seen from the eastern shore of 
the hike, this girdle of vegetation appears Hke a dusky cloud-band encir- 
clin;^ tlie mountain; above which rise the bare and rugged peaks forming 
the crest of the range. Besides the coniferous trees the mountain mahogany 
and the cottonwood are common in some portions of the old lake basin. 
The former grows in the cafions and ravines of the mountains, while the 
latter is found mostly along the streams, whose courses it renders conspic- 
uous by deep green foliage in summer, and the brilliant yellow of ripened 
leaves in autumn. 

With the few exceptions we have mentioned, the mountains of the La- 
hontan basin are desert ranges, frequently brilliant in color, and present a 
diversity of tints that are astonishing to one reared beneath more humid 
skies, but lacking in the shades and shadows that vegetation alone can im- 
part. In this region the mountains are nearly all of volcanic rocks, among 
which the deeply colored rhyolites are conspicuous. Still more diversified 
are the purple trachytes of many hues, and volcanic tuffs that vary through 
all shades and tints, from a pure white to a deep, luminous red. In con- 
trast with these harlequin colors are sombre mountains and rugged cliffs of 
basalt, sometimes veiled and partially buried beneath dunes of soft, creamy 
sand. The traveler over the Carson and Colorado Railroad, while passing 
along the eastern shore of Walker Lake, cannot fail to be impressed with 
the gorgeous coloring of the rhyolite hills bordering the valley on the east, 
especially if his journey be made in the deepening twilight, when the splen- 
dor of the western sky is rivalled by the brilliant coloring of the silent and 
Hfeless mountains. The West Humboldt Mountains, bordering Humboldt 
Lake on the east, are also remarkable for the great variety of beautiful tints 
that are inherent in the rhyolite > and tuffs composing the range. The abso- 
lutely desert mountains stretching northward from Black Rock Point, and 
known as the Black Rock Mountains, are so gorgeous and varied in color 
that they merit the name of the Chameleon Hills. The nearly parallel 
range to the west of these mountains has been called the ''Harlequin Hills," 
by Mr. Webster. The aptness of the name will no doubt be appreciated by 
every one who has seen those naked towers and domes of rhyolite and tuff 
at sun rise or at sunset, when their glories are fully revealed. 



40 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

RIVERS. 

The rivers that ^nter the Lahontau basin are the Humboldt, from the 
east, Quinn River, from the nortli, and the Truckee, Carson, and Walker, 
from the west and southwest. All these streams flow through partially filled 
cafions which bear evidence of having been excavated by stream erosion 
previous to the first rise of Lake Lahontan. These rivers, like most others 
in the Great Basin, vary greatly in volume during the year. In winter and 
spring they become broad, rapidly flowing floods of muddy water that over- 
spread their banks, but during the dry season, from May to November, they 
shrink greatly in volume, and sometimes become dry for a large part of 
their course. 

THE HLMBOT^DT RIVER. 

This river ^* rises on the eastern border of Nevada and flows westward 
for approximately 200 miles, and enters the Lahontan basin through a pass 
in the Sonoma Mountains, in latitude 41'^. From this point it continues 
its course through* Lahontan lake-beds for nearly 100 miles to Humboldt 
Lake. Throughout the dry season this is usually its terminus, but during 
the winter months the lake frequently overflows, and the river continues 
to North Carson Lake (** Carson and Humboldt Sink"), where its waters 
are evaporated. The Humboldt before entering the Lahontan basin receives 
a number of tributaries, the largest being Reese River, which enters from 
the south. During the summer and fall many of these streams, including 
Reese River, fail to reach the main channel, their waters being dissipated 
by evaporation or absorbed by the thirsty soil. In its course- through the 
Lahontan lake-beds between Golconda and Humboldt Lake, the river has 
carved a cation, in places 200 feet deep, since the recession of the former 
lake. The material removed in cutting this channel has been deposited in 
the northern part of Humboldt Lake, and has contributed largely to the 
formation of a broad low-grade delta that is already partially converted into 
rich meadow-lands. 



'^ Named Huml>oldt by Fremont, but was previously known as Mary's, or Ogden River. See Fr6* 
niont'H Geographical Memoir upon Upper California, Washington, 1848, page 10. 



RIVERS OF THE LAHONTAN BASIN. 



41 



Two measurements were made of the volume of the Humboldt, one 
on September 10, 1881, the second July 17, 1882 ; the former gave 48 and 
the latter 750 cubic feet per second. When the first measurement was taken 
the river was at its lowest stage for the year. At the time of the second 
measurement it was flooded, and lieavy with sediment, but had fallen three 
feet below the line that recorded its highest rise; two weeks later its dis- 
charge had decreased nearly one half. 

An analysis by Dr. T. M Chatard of the water of the Humboldt, col- 
lected November, 1882, near Stone House, just before the river enters the 
Lahontan basin, is given below. 



CunstitnentH. 



Silica (SiOt) 

Alumina (AltOs) 

Calciam (Ca) 

Ma^OiesioD^ (Mg) ... 

Pot4i88ium (K) 

Smliuin (Xa) 

Sulphuric acid (SO4) 
Cliloiiue(Cl) 



('arbonic acid (CO3) by diflferenoe. 
Total 



One liter of 
watvr con- 
taioH, in 
grainmea— 


Per cent, in 
total solidA. 


0. 0326 


9.03 


0. 0013 


0.37 


0. 0489 


13. 53 


0.0124 


1 3. 46 


0. 0100 


2. 77 


0. 0467 


12.92 


0. 0477 


13.12 1 


0. 0075 


2.08 


0. 2071 


57. 28 ■ 


0.1544 


42.72 



Couatituenta. 



Probable com- 
bination (in 
grammes per 
liter). 



vSilica (SiO,) 

Alnrnina ( AUOj) . . 

Calcium c. irbouHt« (CaCog) 

Mngnc'siuin carbonate (M£CO|) 

i'otnsaium chloride (KCl) 

Potassium carbonate (KzCOs) 

Sodium sulpliate (Na*So4) . ..• ' 

Soiliuni carbuutite (NasCos) 

I 

Total (95.52 por cent. nrcount»*d for) 



0.0326 
0. 0013 
0. 1222 
0. 0434 
0. 0157 
0. 0046 
0. 0705 
0. 0550 



0. .3453 



0.3615 



100. 00 



If excess of CO3 above amount retiuired for Na^Coj be calculatecl as XaFiCoj, we will have 0.3458 lesn Na^Cot 
(U.0550) =0.2903 
NatfCoj =0.0200 
NaHCo3— 0.0512 



Total.. 0.3615 



An analysis of the water of Humboldt Lake is given on page 67. 

QUIXN RIVER. 

Quinii River is formed by the union of many brooks that have their 
sources on the Santa Rosa Mountains and on the eastern slope of the Quinn 
River Range. It flows south for about fifty miles down Quinn River Valley 
and then turns abruptly westward, and continues its course until the north- 
em end of the Jackson Range is passed ; it then flows southward again and 
enters the Black Rock Desert. During the spring months, while the snow 
on the mountains is melting, this is a good-sized river, and has a swift 
muddy current. At Mason's Crossing, some 75 miles from its source, it is 



42 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



reported to be impasfiable for horsemen for a number of days together dur- 
ing the high-water stage. At this season its waters fbrm a shallow lake of 
variable size, on Black Rock Desert, that is said, at times, to be 50 or 60 
miles long by 20 broad. As the dry season advances, this playa lake 
evaporates, leaving a vast mud-plain; the river at the same time shrinking 
back 75 or 100 miles. During the highest stages of Lake Lahontan, Quinn 
River had no existence, the greater part of its valley being occupied by an 
arm of the lake. 

TRUCKBB RITER. 

The Truckee River has its source in the overflow of Lake Tahoe and 
is of greater purity and subject to less fluctuation than any other stream 
that enters the Lahontan basin. The lake which gives it birth is situated 
at an elevation of 6,247 feet^^ amid the peaks of the Sierra Nevada; from 
this reservoir the water descends with a fall of 2,466 feet,^® to Pyramid and 
Winnemucca lakes, where it is evaporated, leaving the lower lakes alkaline 
and saline. The river is quite largely used for irrigation in the neighbor- 
hood of Reno, and to a small extent between Reno and Wadsworth. A few 
miles from Pyramid Lake a good-sized ditch has recently been constructed 
for the irrigation of the lands of the Indian reservation. 

An analysis of the waters of Lake Tahoe, by Prof. F. W. Clarke, which 
may be considered as representing the normal condition of the Truckee 
River, is given herewith: 



Constitnento. 



8iUca(SiO») 

MagneBiam (Mg) . . . 

Calciuin (Ca) 

Sodinm (Na) 

PutaBsiiim (K) 

Chlorine (01) 

Salphnric acid (SO4) 



Carbonic acid (COt) by difference. 
Total 



One liter of 
water con- 
tains, in 
grammea— 


Per cent, in 
total solids. 

ia77 


0.0187 


0.0030 


4.11 


0.0093 


12.74 


0.0073 


10.00 


0.0033 


4.52 


0.0023 


3.14 


0.0054 


7.40 


0.0443 


06.68 


0.0287 


39.32 


0. 0730 


100.00 



Constituents. 



SUica(SlO») , 

Mapn^esiam carbonate (MgCot) 

Caloinm carbonate (CaCoa) 

Sodium chloride (NaCl) 

Potassium chloride (KCl) 

Sodinm sulphate (NatSo4) 

Potassium sulphate (KtSo«) 

Sodium carbonate (NasCot) 

Total (99.04 per cent, accounted 
for) 



Probable com- 
bination (in 
grammes per 
liter). 



" Determined by Pacific Railroad sarveys. 

"Eleyation of Pyramid Lake, 3J81 feet. SeejpotfM, page 101. 



0. 0137 
0. 0105 
0.0232 
0.0012 
0.0034 
0.0052 
0.0034 
0.0117 



0.0723 



RIVERS OF THE LAHONTAN BASIN. 43 

The sample, the analysis of which is reported, was collected in October, 
1882, on the eastern border of the lake near Glen Brook, one mile from 
shore and one foot below the surface. 

The most interesting feature to the geologist in the present condition 
of the Truckee River is its bifurcation shortly before reaching Pyramid 
Lake. As represented on Plate IX, the stream divides so as to deliver a 
part of its waters to Pyramid Lake and a part to Winnemucca Lake. The 
branch entering Pyramid Lake has the ordinary features of a river winding 
through an alluvial bottom, and has formed a low-grade delta of broad 
extent, as shown on the map. The waters that are tributary to Winne- 
mucca Lake leave the main stream at nearly a right angle and flow through 
a deep narrow channel carved in Lahontan sediments. This stream, or 
**slough," when measured in September, 1882, had a volume of 2,400 cubic 
feet per second From the manner in which the bifurcation takes place it 
cannot be considered as the breaking up of a stream on a delta or an 
alluvial slope, as in the case of the Carson River after entering the Carson 
Desert, but must have been originated by the waters overflowing from 
Pyramid to Winnemucca lakes, or vice versa. This matter, however, will 
receive further consideration in connection with the fluctuation of Pyramid 
and Winnemucca lakes (page 63). 

CARSON RIVER. 

The Carson River rises on the eastern slope of the Sierra Nevada, south 
of Carson City, and, after flowing 60 or 70 miles, enters the Lahontan basin 
through a deep cafion at Dayton. From this point to the Carson lakes its 
course is through a channel carved in Lahontan lake-beds. Near its mount- 
ain source its waters are fresh and pure, as mountain streams usually are, 
but in passing through Carson and Eagle valleys, once occupied by Qua- 
ternary or late Tertiary lakes, its waters become somewhat impregnated 
with soda salts, and in its course through Lahontan lake-beds this percent- 
age is increased. The waste from a large number of stamp-mills now pol- 
lutes the river to such an extent that it was not thought desirable to have 
its waters analyzed. The valley of the Carson from Eagle Valley to Carson 
Desert was largely excavated by stream erosion in pre-Quaternary times, 



44 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



as U shown by the fact that from Dayton to the Carsou Desert it was occu- 
pied by the waters of Lake Lahontan. During tlie existence of the lake 
the valley became deeply filled with lake sediments and delta deposits, 
which were re-excavated as the lake fell. The present gorge is the work 
of the second period of excavation The structure of the cafion between 
Clmrchill Valley and the Carson Desert is represented in the following ideal 
section, which shows the older cafion in volcanic rock partially filled with 
lacustral sediment, and the second carved out of stratified lake-lieds. 




Fm. B.— Ncal cnwt-arcllon of Canou Blver Ci>nc»i. Nmila. 

Measurements of the volume of the Carson Itiver at Old Camp C'liurcli- 
ill, July 1, 1881, gave between 4.'»0 and 500 cubic feet per second as the 
volume of tlie stream ; in September, 1883, the discbarge was less than half 
this amount. * 

The bifurcation of the Carson River after entering the Carson Desert 
is represented on the accompanying map (Plate VII). For tiie history of 
the changes that the river has undergone during the last few years 1 am 
indebted to some of the early pioneers, who made this region their home. 
Previous to 1862 it flowed into the South Carson Lake, but there was an 
abandoned channel branching from it and leading northward. During a 
time of unusually high water in the spring of 18fI2 tlie river bifurcated, 
the old channel was reoccupied, and a branch flowed to each lake. The 
point at which the river divided is indicated on the map by the date 18fi-2. 
Previous to that time there was a " slough " connecting the North and South 
Carson lakes through which the waters flowed northward. After the forking 
of the stream the South lake was lowered so that it no longer overflowed, 
and the water in the slough became stagnant Anotlier flood occurred in 
the spring of 1867 or 1869, which caused the arm emptying into North 
Carson Lake to branch and send a stream eastward to the slough. The last- 



Hill > iku oi ■••!.» II • 'M tiiiiii ^ i">m iri i 

■ ^ 5€ .il.« III Mili* 



S « j|_ i I O _i li» 11 *•• 








/ 



-.^•t^ '1 ^_^ 



fAHSON DESKltr. NKVADA 



RIVERS OF THE LAHONTAN BASE^. 45 

formed channel is still occupied, and is known as '*Ne\v River." This dis- 
tribution of the waters of the Carson still continues, but is regulated, at 
least in part, by slight willow dams at the points of bifurcation. Since 
1862 the slough connecting the two lakes is reported to have reversed its 
current in some instances, according as the water in the North or South 
Lake was the higher. In June, 1859, the water in the slough was reported 
by Captain Simpson to be 50 feet wide and 3 or 4 feet deep, and flowing 
northward with a strong current.^^ In September, 1866, Lieut. R Bii-nie*^^ 
states that the waters were sluggish, with scarcely a perceptible flow. In 
June, 1881, I found the volume of water about the same as reported by 
Simpson in 1 859, and flowing northward with a well-marked current. In 
September, 1883, the slough was low, and did not exhibit any motion ; 
South Carson Lake at the same time was very shallow, much of it present- 
ing the appearance of a swamp. 

While viewing the Carson Desert from the surrounding mountains one 
may trace, as cm a map, the various branches of the river meandering 
through the monotonous plain, by the lines of vivid green cottonwood 
trees that mark their courses. 

WAJLKKR Rl^ ER. 

This stream rises on the eastern slope of the Sierra Nevada in two 
main branches between which there is a grand mountain mass knowu as 
t^e Sweetwater Range. The east fork of the Walker River receive? the 
drainage from the eastern slope of the Sweetwater Range, and from the 
western slope of the less picturesque Wassuck or Walker River Range. 
The west fork flows at the base of the main range of the Sierra Nev ida, 
and once formed a chain of small lakes, probably of Tertiary age, w'lich 
cut deep channels of discharge and were drained dry. These basins 
are now level-floored valleys, connected by narrow and almost impas- 
sable canons. The two branches of Walker River unite a little brlow 
the point where they formerly entered Lake Lahontan, and thence How 
through Mason and Walker River valleys to Walker Lake. At the north 

^» Exploration Across the Great Basin of Utah, Washington, D. C, H:J76, p. 85. 
20 Annual Report of the Chief of Engineers, U. S. A., 1877, p. 1264. 



46 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



end of Mason Valley the river bends abruptly southward, at the same 
time increasing the depth of its channel, which soon becomes a caiioii 
through lake-beds similar to the ones carved by the Humboldt and the 
Truckee. Captain Simpson reports the Walker River near its mouth to 
have been about 100 yards wide and from G to 10 feet deep on June 7, 
1859.^^ A measurement of the volume of the river about 3 miles from 
its mouth, June 4, 1881, gave 400 cubic feet per second as the rate of flow. 
In October of the following year its bed was dry, and little, if any, water 
reached the lake from this source. This decrease during the dry season is 
evidently due in a great measure to the extensive use of its waters for irri- 
gation in Mason Valley. As a rough average, the data at hand being 
inexact, I have assumed 200 cubic feet per second, or 700,000,000 cubic 
yards annually, as the approximate discharge. An analysis of a sample of 
water collected October, 1882, at a point just below where the main branches 
of the river unite, is reported by Prof. F. W. Clarke, as follows: 



Constituents. 



One liter nf 
water con- 
tains, in 
grammes- 



Silica (SiO«) 

Calcium (Ca) 

Magnesium (Mg) 

I'otassinm (K) 

Sotlinm (Na) 

Chlorine (CD 

Sulphuric acid (SO4) 

Carl>onic acid (COa) by difference 
Total 



Per c*.ut. in 
total solids. 



0. 0225 


12. .50 


0. 0228 


12.60 


0.0038 


2.12 


Trace. 




0.0318 


17.67 


0. 0131 


7.28 


0.0284 


15.77 


0. 1224 


68.00 


0. 0570 


32.00 


0. 1800 


100.00 



Constituents. 



Silica (5iOf) 

Calcium carbocate (CaCOs) 

Magnesium carbonate (MgCOs) 

Sodium chloride (NaCl) 

Sodium sulphate (NatSOO 

Sodium oarbonate (NatCOs) \... 

Total (90.39 per cent, accounted 
for) 



Probable com- 
bination (in 

frrammes per 
Iter). 



0.0225 
0. 0570 
0.0133 
0.0216 
0.0421 
0.0224 



0.1780 



The measurements of the volumes of the rivers of the Lahontan basin 
at different seasons indicate the great fluctuations to which the drainage in 
a desert country is subject. The rivers are flooded during the winter and 
spring — which includes the rainy season, and also the time when the mount- 
ain snows are melting most rapidly — and diminish greatly in volume during 
the parched and arid summer months. The Truckee River is an excep 
tion to this rule, as it is the overflow of a great reservoir, Lake Tahoe, 



^> Exploratious Across the Great Basin of Utah, Washington, D. C, 1876, p. 87. 



SPRINGS OF THE LAHONTAN BASIN. 47 

which serves to equalize its volume, as well as to clear its waters of im- 
purities in suspension. A knowledge of the composition of the rivers 
entering the Lahontan basin and their average volume enables one to esti- 
mate roughly the amount of mineral matter in solution that these streams 
are now contributing to the lakes that they supply. This subject will be 
reverted to in discussing the chemical history of Lake Lahontan. 



SPRINGS. 

Springs have been grouped with reference to their mode of occurrence, 
in two convenient classes: («) Hillside springs and (b) Fissure springs. 

Hillside springs are usually formed by the gathering of percolating 
meteoric waters in inclined porous strata, which alternate with less pervious 
beds, and outcrop on a hillside or among mountains in such a manner as to 
afford an escape for the subterranean waters. The source of the water 
forming hillside springs is in the rainfall of the immediate neighborhood. 
They are commonly small, and their temperature is approximately the same 
as the mean temperature of the locality at which they are found. Springs 
of this class are usually agreeable to the taste and useful for domestic pur- 
poses, for the reason that they are seldom highly charged with mineral 
matter. 

In western Nevada the conditions favoring the formation of hillside 
springs are almost entirely absent. Tlie rocks throughout the region are 
very largely volcanic witliout definite stratification, and the rainfall is lim- 
ited to a few inches annually. Owing to these unfavorable conditions, there 
are no springs of this class in the Laliontan basin to claim our attention. 

Fissure springs occur where the earth's crust has been broken, usually 
with some displacement, to a great depth. Their water supply, as in the 
first instance, is from meteoric sources, but is derived from regions remote 
from the point of discharge. Owing to the depth to which tlie water of 
fissure springs frequently descends during its subterranean passage, it is 
commonly highly heated and not unfrequently reaches the surface with the 
temperature of boiling water. The heat and the great pressure to which the 



48 GEOLC GICAL HISTOUY QF LAKE LAHONTAN. 

water is subjected during its underground passage render it an active 
solvent. Hot springs are therefore frequently charged with a great variety 
of mineral substances in solution. 

The Lahontan basin, in common with the entire northern half of the 
Great Basin (the southern portion, not being so thoroughly explored), is 
remarkable for the number of springs which rise from a great depth through 
fissures. These almost invariably occur along lines of displacement, and 
range in temperature from 50^ or 60^ F. up to the temperature of boiling 
water for the elevation at which they occur. 

The springs of the Lahontan basin are indicated on the accompanying 
map, Plate VIII; their maximnm temperature when known being shown 
by figures in red. 

As springs performed an important part in the history of Lake Lahon- 
tixn, we shall devote a few pages to the description of those now rising in 
its basin. A knowledge of the phenomena they now present will assist in 
interpreting the records of the similar springs that flowed long ago. 

Beginning at the south, the first group of springs requiring notice is 
found in the northern part of Mason Valley, about one mile northward of 
Wabusca station. These springs occur in circular basins, sometimes at the 
tops of low mounds, and are of all degrees of temperature, from about the 
mean of the region up to 162° F. The water flowing from them is clear 
and sparkling, but is somewhat alkaline to the taste, and contains a small 
percentage of sulphate and carbonate of soda, common salt, etc. The water 
collecting in small basins on the desert is evaporated, and has formed a 
saline deposit of considerable extent, a section of which is given below: 

White, hard crust of sulphate of soda, with coiiuuou salt, some calcium carbou- 

ate, etc . • iuches . . 1-2 

Soft, mealy or clayey deposit of sodium sulphate, calcium carbonate, calcium 

sulphate, etc . . inches . . 2-7 

Clear transparent crystals of sodium sulpliate, with some eartliy impurities, rest- 
ing on saline clay feet. . 6-8 

The surface of the desert about the more abundant accumulation of 
salts is covered over a large area with a white saline eflflorescence. These 
springs occur in an east and west line, that coincides with the course of a 



U S. GEOLOOICAL SURVFTT 



JiAKK LAK0K1AN PL VlTT 



120* 



119* 



118" 



r^^'^T 






If 



:t\ 



•y 



. ; >» • ' 



• • 



~"a - -iT i 



SPRINGS OF THE LAHONTAN BASIN. 



49 



post-Lahontan fault which is pLiinly shown by an irregular scarp, in some 
places 20 feet high. 

Allen's Springs are situated on the southern border of South Carson 
Lake at the base of a high basaltic butte which once formed an island in 
Lake Lahontan. These springs at present are very small, the discharge at 
the surface being less than half a gallon per minute. In this desert coun- 
try even this meager supply is important, as it is the only drinkable water 
within a radius of over twenty miles. These springs are of interest to the 
geologist because of their antiquity. The amount of yellowish, porous, 
tufa deposited about them indicates that the flow of water was formerly 
more copious than at present, and at various times has issued from a num- 
ber of orifices. Much of the tufa that is plainly a spring deposit is incrusted 
with thinolite and dendritic tufa which we know was precipitated from the 
waters of Lake Lahontan, and shows that the springs were in existence at 
least as early as the middle Lahontan period. 

The Hot Spring, at Hot Spring station on the Central Pacific Railroad, 
as shown by Dr. T. M. Chatard's analysis, has the following composition: 



CooBtitiieutii. 



Smca(Si()«) . 

AliiToinum (Al) 

('alclnm (Ca) 

MagneHlum (Mj;) ... 

PotaMsinm (E) 

Litham (Li) 

Soilium (Nb) 

Chlorine (CI) 

Sulphuric acid (SO4) 
Ox.vgeD* in SiO, 

Total 



Ono lit^r of 
water con- 
tains iu 
gram me*) — 


l*er <'ent. in 
total HolidH. 


0. 2788 




11.14 


0. 0010 




0.04 


0. 0305 




l.lKi 


0. OOIU 




0.04 


; 0.066U 




2.69 


Trace. 




Tra<o. 


0. 7743 




31. 04 


0. 9G79 




38.79 


0. 3555 




14.25 


0. 0194 




0.78 



C.'onHtitiientH. 



Probable com- 
binat ion (in 

{grammes per 
it«r). 



Silica (Si()j) 

SfNliiiiii nilicate (XaSiOa) 

Aliiiiiiiiuiu Htilphate (Al[S()4li) 

Calciuiii Hiilpliato (('aSOj) 

Ma^incNiuni Hiilphate (MkSo4) 

Sodium sulphate (NaSo4) 

Sodium chloride ( XaCl) 

Potatisium chloride (KCl) 



0.2060 
0.1480 
0.0083 
0.1037 
0.0050 
0.4039 
1.4946 
0.1278 



Total 



2.4953 



2. 4953 



100. 00 



Extra oxygen in Hilicate. 



No carbonij- acid in leKiduo left by evaporation. 



At a number of orifices the waters of this spring issue in a stiite of ac- 
tive ebulHtion. When the openings become obstructed the steam escapes 
with a hissing and roaring sound. The spring occurs in a line of recent 
faulting, and has evidently been crowded southward as the deposits from 

the waters closed the previous channels of discharge. On cooling, an 
MoN. XI — 4 



50 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

abundant deposit, consisting principally of common salt and sodium sul- 
phate, is found. At one time these waters were thought to contain sufficient 
boracic acid to be of economic importance, and an attempt was made to 
separate it, but the experiment was a failure. There is no evidence to 
show that this spring was active during the existence of Lake Lahontan. 

A number of small springs, some of which are warm, occur on 
the west side of Winnemucca Lake. Farther northward small springs of 
pure cold water have been found on both sides of the Selenite Range.^ 
Near the north end of this range, but isolated from it, stands Hot Spring 
Butte, once a small island in Lake Lahontan. The butte derives its name 
from a copious spring with a temperature of 180^ F. which discharges about 
20 gallons per minute. The water flows northward for about a mile, and 
forms a shallow pool in the desert, where it is evaporated. Other hot 
springs occur northward of Hot Spring Butte, near the southern end of the 
Jackson Range. 

Numerous copious springs of all temperatures, from the mean of the 
region up to the boiling point of water, come to the surface along the west- 
ern border of the Lahontan basin, from Honey Lake Valley to the Oregon 
boundary. The majority of these have formed circular basins that are 
filled with beautifully clear water, and are sometimes of great depth, as in 
the cas^ of Deep Hole, Round Hole, and the group at the east end of 
Granite Mountain. The bottoms of the basins are usually of flocculent 
mud, through which the water issues, frequently accompanied by bubbles 
of gas. In common with very many other hot springs, these basins are lined 
with deep green confervoid growths. Many of the springs in the belt indi- 
cated exhale sulphurretted hydrogen, and deposit amorphous, calcareous 
tufa In one instance silicious sinter is precipitated as the water cools. 
All the springs in this belt occur either on fault lines that have been 
disturbed by orographic movement since the withdrawal of the waters of 
Lake Lahontan, or are very closely related to such lines of displacement. 

^Tbis range is about 30 miles long aud extends from the north end of Winnemucca Lake to Hot 
Springs Butte; it is structurally distinct from the Natcbesor Truckee Range, which follows the eastern 
shore of Winnemucca Lake. I have named it in reference to extensive deposits of crystallized gyp- 
sum or selenite that outcrop along its western border. 



SPRINGS OF THE LAHONTAN BASIN. 



51 



The character of these recent fauhs will be described in the chapter devoted 
to post-Lahontan orographic movements. 

The springs in this belt are too numerous to receive detailed descrip- 
tion, and we can onl}^ notice a few of the most important ones. The most 
copious single spring in the series occurs near the northern shore of Honey 
Lake, designated as Schaffer's Spring on the accompanying map, and dis- 
charges about 100 cubic feet of boiling water per minute. The ebullition 
is 80 energetic that the water is thrown in a column to the height of 3 
or 4 feet. An analysis of this water by Dr. T. M. Chatard shows the fol- 
lowing composition : 



CoDBtituent«. 



Smoa(SiO,) 

Calcium (Ca) 

Magnesinin (Mg) — 

Sodium (Na) 

Potaaaium (K) 

Chlorine (01) 

Salphuric acid (SO4) 
Oxygen * (O) 

Total 



One liter of 
water con- 
tains in 
gramroea — 


Per cent In 
total solids. 


0. 1310 


12.83 


0. 0121 


1.18 


0.0004 


0.04 


0.3040 


29.78 


0.0094 


0.92 


0.2070 


20.27 


0.8492 


34.19 


0.0080 


0.79 



Constituenta. 



Silica (SiO-/) 

j Sodium silicate (NatSiOa) 

Calcium sulphate (CaS04) 

Magnesium sulphate (MgS04) 
Sodium snlphatxf (NasSOi) 

I Potassium chloride (KCl) 

Sodium chloride (NaCl) 



Probable oom* 
bination (in 
grammes per 
Uter). 



Total (99.93 per ct accounted for) 



1. 0211 



100. 00 



0.1008 
0.0618 
0.0409 
0.0020 
0. 4716 
0.0180 
0.3206 

1. 0211 



* Oxygen necessarily added to form NaiSiOt. A slight trace of Coa in re»idue left on evaporation. 

This spring occurs at the southern end of a long row of tufa crags, fully 
50 feet high and somewhat greater in breadth, a few of which still have small 
springs issuing from their bases. The tufa at the base of the crags, and 
forming the nucleus of the deposit, is amorphous, but is coated with a heavy 
deposit of the dendritic variety hereafter to be described. The former was 
a direct precipitate from spring water, but the latter was as plainly depos- 
ited from the former lake. The evidence is such as to lead to the conclu- 
sion that this spring was fully as copious during the existence of Lake La- 
hontan as now, and that its point of discharge was crowded southward along 
a fissure as its former outlets became filled with calcareous tufa deposited 
from its own waters. 

About 5 miles southeastward of the spring described above occurs 
a group of springs covering several acres and discharging a very large vol- 
ume of heated water, which issues at so many orifices that no estimate of 



52 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

the total outflow could be obtained. At a number of points the tempera- 
ture of the water approximates to the boiling point, and, on cooling, depos- 
its a limited quantity of calcareous tufa. A qualitative examination indi- 
cates that these springs have about the same chemical composition as the 
water of Schafl*er's Spring, an analysis of which is given above. 

High Rock Spring, situated 5 miles eastward of the group described in 
the last paragraph, occurs at the base of large tufa crags of Lahontan date, 
and has a temperature of 100° F. Its waters are used for irrigation, and 
are inhabited by both fish and mollusks. This spring is evidently of consid- 
erable antiquity, as the tufa crags deposited from its waters are coated with 
heavy layers of calcium carbonate that have a dendritic structure and were 
without question deposited from the lake waters which once flooded the 
valley. 

None of the numerous springs on the western border of Smoke Creek 
Desert are remarkable for their high temperatures, but a number are ther- 
mal, and nearly all bear indications of having been hot springs at some 
former time There is no evidence that any of these springs were in exist- 
ence during the time when Lake Lahontan covered the desert 

On the border of the desert at the eastern end of Granite Mountain a 
group of circular basins filled with heated waters from a subterranean source 
covers a considerable area. A number of these basins furnish water of won- 
derful transparency, which ovei'flows to "the eastward, and on evaporating 
leaves a saline incrustation that covers many acres. Others occur in the 
tops of low mounds and are caldrons of boiling mud that occasionally erupt 
and discharge their tenacious contents to a distance of 30 or 40 feet. This 
group is known as the Mud Springs. 

The most copious outflow of hot water in tlie Lahontan basin occurs 
in a small embayment of the ancient lake a few miles north of Granite 
Mountain. This is a group of springs several acres in extent which fill cir- 
cular basins in the tops of low mounds that have been formed to some 
extent by spring deposits, but are largely composed of vegetable growths 
mingled with aeolian sand and dust. These springs vary through all degrees 
of teujperature, from 50*^ to b*0° F. up to that of boiling water, and their 
discharge forms a creek of heated water of considerable size that pours into 



SPRINGS OF THE LAHONTAN BASIN. 



53 



a deep basin and becomes ponded before spreading out over the desert and 
evjiporating. Many of the basins in this group are hned with anior})hous 
calcareous tufa ; and one, filled with boiHng water, is depositing both silica 
and tufa. The siliceous sinter precipitated from these waters is gelatinous 
at first, but soon hardens and forms mushroom-shaped scollops which fringe 
the sides of the basin and the margins of the channel of discharge. The 
deposition of silica takes place quite rapidly as the water cools, and in some 
instances imprisons insects that have been killed by venturing into the boil- 



mg waters. 



An analysis by Dr. T. M. Chatard of one of the most typical of the 
springs in the group described briefly above, from which calcareous tufa is 
being deposited, is given below : 



ConAtitncDtfl. 



Silica (SiO«) 

Calcium (Ca) 

MatiDPHiani (Mj;) . . 
ScMlium (Mm) 

PotaiMinni (K) 

Litbiain(Li) 

Chlorine (CI) 

Sulphuric acid (SOj) 

Oxygen * (O) 

Carbonic acid (COs) . 



One liter of ! 
water con- 
tainH in 1 
)Cramine8 — 


Per cent, in 
total HolidH. 


0. li:U) 




9.60 


0.(067 




3.10 


0. 0034 




J9 


0. 3r>f>4 




30. 03 


0.0191 




1.61 


'rra<'«». 




Trace. 


0. 2396 




*J0. 25 


0.3901 




32. 97 


0. 0255 




2. 15 


Trace. 




Trace. 



Const ituentji. 



Silica (SiOf) 

Sodium silicate (NOtSiOj) 
Calcium sulphate (CaS04) 
MafHiesium .sulphate (Mj2S04) 
Sodium sulphate (NftxSOa) .... 
Potassium chloride (KCl) 
Sodium chloride (NaCI) . . 



Probable com- 
bination (in 
grammes per 
liter). 



0.0180 
0.1942 
0.1247 
0170 
0.4267 
0.0363 
0.3665 



Total (99.43 perct. accounted for) 



1.1834 



ToUl 



1.1834 



100.00 



* Oxygen ueceMsarily abided to form Na^SiOj. 

Hot springs of considerable volume occur in groups near the southern 
end of Black Rock Point and along both the eastern and western borders 
of the Black Rock Range, and also on the borders of the desert at the east- 
ern base of the Pine Forest Range. Continuing northward, the belt of hot 
springs we have been tracing is re})resented in Pueblo Valley by two steam- 
ing caldrons, and at the eastern base of Stein Mountain other outleti^ of a 
similar nature have been examined. Nearly every spring throughout the 
entire region between Honey Lake Valley, California, and Alvord Valley, 
Oregon, a distance of over 200 miles, has been observed to occur on a line 
of recent displacement. 



54 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

In all, there are at present between fifty and sixty groups of hot springs 
in the Lahontan basin ; the total number of individual outflows cannot be 

estimated at less than two or three hundred. It is impossible to estimate 
the amount of water entering the basin from subterranean sources with 
even an approximation to accuracy, but if gathered in a single stream it 
would form a river comparable in size with the Humboldt during the sum- 
mer season, the volume of which would remain practically constant from 
year to year. The temperature of this imaginary river would be far above 
the normal for the region ; and in composition it would be much richer in 
dissolved minerals than ordinary surface streams, as is indicated by the 
accompanying analyses. 

It is certain that many of the hot springs now flowing were in exist- 
ence during the time that Lake Lahontan flooded the valleys of northwest- 
ern Nevada; and it is believed that the three analyses given above not only 
represent approximately the average composition of the springs now flowing, 
but also indicate the character of the thermal waters that entered the ancient 
lake through fissures in its bottom. 

EXTINCT SPRINGS. 

At many points in the Lahontan basin, as mentioned in the preceding 
pages, we find deposits made by springs which are now extinct. The majority 
of these are composed of calcareous tufa that was precipitated about sub- 
lacustral springs, and will be described in the chapter devoted to the chem- 
ical history of the former lake. A group of spring-mounds about half a 
mile southward of Humboldt House and on the west side of the Central 
Pacific Railroad track, are, however, of a different nature. They are low 
domes composed principally of calcareous tufa, open at the top and filled 
within with crystallized gypsum impregnated with sulphur. The presence 
of sulphur has led to some exploration, but the supply is evidently too lim- 
ited to be of much economic importance.^ The mounds in this group are 
broad and comparativel} low domes, formed of thatch-like layers of calca- 
reous tufa with considerable quantities of siliceous sinter, especially about 

^ These sulphur deposits were the ouly ones that could be found by the writer in the neighborhood 
of Humboldt House, and are thought to be the ones described in the reports of the United States 
Geological Exploration of the Fortieth Parallel, Vol. II, p. 742. 



LAKES OF THE LAHONTAN BASIN. 55 

their bases. These deposits are unlike the greater part of the old tufa 
structures occurring abundantly in the same basin, especially in the neigh- 
borhood of Pyramid Lake, but agree in form and structure with the rings 
and domes now forming about many subaerial hot springs; thus indicating 
that the deposits in question are of post-Lahontan date. The presence of 
siliceous sinter also indicates that these deposits were of subaerial origin, as 
no precipitates of this nature from sublacustrine springs are known. 



LAKES. 

At present there are seven lakes in the Lahontan basin. These are 
Honey Lake, California; Pyramid, Winnemucca, Humboldt, North Carson, 
South Carson, and Walker lakes, Nevada. To these we may add the two 
Soda lakes near Ragtown, Nevada, as occurring in the same basin, but 
these are of a decidedlv different character from those enumerated above, 
and will receive special attention. These lakes are of assistance to the 
geologist in interpreting the history of the great lake which formerly 
flooded all their valleys; we shall, therefore, describe them somewhat 
minutely. 

HONEY LAKE. 

Honey Lake Valley was occupied by the western arm of Lake Lahon- 
tan, and became deeply filled with lake sediments. At present it is a broad, 
level-floored, sage-brush-covered plain, with fruitful areas on its western and 
northern borders where water is available for irrigation, and has an abso- 
lutely barren playa of considerable extent on its eastern margin near Fish 
Spring. The lake occupies a shallow depression in the western part of the 
valley, and may be classed as a playa lake, as it is without outlet and be- 
comes completely desiccated during seasons of unusual aridity. It is sup- 
plied principally by Susan River, which enters it from the northwest ; but it 
receives some tribute during the rainy season from Long Valley. The hot 
springs along its northern border also furnish considerable quantities of 
water. The area of the lake varies with the seasons, as well as from year 
to year, as is common with all inclosed lakes. As mapped by the survey 
in charge of Captain Wheeler, in 1H67 it covered an area of approximately 



56 GEOLOGICAL UlSTOKY OF LAKE LAHONTAN. 

90 square miles. In the summers of 1859 and 18G3 it is reported by the 
settlers in the. valley to have become completely desiccated, leaving a broad 
smooth plain of cream-colored mud Its average depth in the summer of 
1877 is reported by Lieutenant Symonds'^^ to have been about 18 inches. 
In 1882 its greatest depth was 4 feet, but the average, as nearly as could be 
judged, did not differ much from the figures given for 1877. The outline 
of the lake is indefinite, as its shores are usually low and marshy, and in 
places form broad tule swamj)s. Its waters are quite strongly alkaline, 
unfit for human use, and always of a greenish-yellow color, due to the im- 
palpable mud held in suspension. A preliminary examination of the water 
shows that it contains 0.0784 per cent, of saline matter in solution. Quali- 
tiitive tests show the water to be alkaline and charged with chloride of 
sodium, and carbonate and sulphate of soda, together with some potash 
and magnesia. 

PYRAMID LAKE. 

Pyramid Lnke was discovered January 10, 1844, by General Fremont, 
who first saw it from the mountains at its northern end. From the remark- 
able form of an island near its eastern shore its discoverer gave it the name 
which it now bears.^ 

The accompanying map of Pyramid and Winnemucca lakes (Plate IX) 
was made in August and September, 1882, by Mr. Johnson, and shows an 
accurate outline of the lakes as they existed at that time. The soundings 
indicated are from actual observation, the position of the boat at the time 
of measuring the depth being determined with instnnnents stationed on 
shore. The sublacustrine contour lines, drawn at intervals of oO feet, are 
in part conjectural, but are believed to represent approximately the topog- 
raphy of the lake bottom. The north and south axis of l^yramid Lake is 
30 miles in length; in the widest part, near the northern end, its breadth is 
12 miles; farther southward between Anaho Island and the southern end of 
the lake it is contracted to about 5 miles. Its area in September, 1882, was 
828 square miles. Our soundings determined that the greatest depth occurs 

*«Anii. Hep. U. 8. Geojrraphical SiirvejH West of the lOOth Meridian for 1878, p. 115. 
••'^Fr^mont'H First and Second Expeditions, 1842-M:i-'44, i:. S>16. 




R. D. Jj*——. npatrafhtr. 



D AMD WiNNEUUCCA LAKES, NEvAOA. 



LAKES OF TDE LAHONTAN BASIN. 



57 



a few miles north of Anaho Island where the water is .-501 feet deep over a 
very considerable area; showing that the bottom in this portion is a nearly 
uniform i)lain. As the Lahontan beach is 525 feet above the 18H2 level of 
Pyramid Lake, the former lake had a depth of 880 feet, without consider- 
ing, however, the amount of sedimentation that has since taken place. This 
was the dee})est point in Lake Lahontan. 

Pyramid Lake is without outk^t. It receives almost its entire supply 
from the Truckee River, which enters it at its southern end. During the 
rainy season the surrounding mountains send down some tribute, supplied 
princij)ally by two small brooks from the western side of the valley, which 
are living streams for a portion of the year; but the supply from these 
sources is extremely small. As nearly all of the fresh water entering the 
lake is delivered at its southern end the lake varies in salinity as one follows 
it northward. Near the mouth of the '^Fruckee Kiver the waters are suffi- 
ciently fresh to be used for camp purposes ; at the northern end it is far too 
saline and alkaline for human use, but may ])e drunk by animals without 
injury. The waters of Pyramid Lake from two localities and at different 
depths have been analyzed by Prof F. W. Clarke, who reports their com- 
position as follows : 

Water of Pifravthi Lake voUccUd in AuijHHi, 1H,*''»J, at l», nouth of Anaho hland {nee Plate IX). 



ConMitnentM. 



Silica (SiO») 

Ma)!U08itiin (M^) 

enlriiiiii (C'u) 

StNliuQi (Xa) 

PotiiHHiiini (K) 

Cbloriiie (CI) 

Sulphuric iiciil (S()4) . . 

('arlM>iiic acid (('( h* by diir«r<'ucp . . 0. 41)43 



Ouc liter of water 
coDtaiiiH, in IVrcciit in t4ital 
KramnicR per HolidH. 

liter— 



Probable com- 
bioatioD (Id 

f:ramincM p4*r 
Iter). 



II 



1.42«8 



C V !! 



0. <»4i;r. 0. ()3no 



S Z 

1% 

- ? 5 

T, 



1.22 






2.1 .1 



ConHtitnentH. 



aS 
l| 



is 

J! 



0.h« Silica (SiO^) 0.042.'> 0.0300 

0. 07.'i2 0.OP32 2.17 2. 3« MaL>n«Hinni carboDat*; (MgCO,) . . 0.2632 i 0.2912 

Calcium cat iNinate ((*a('Os) , .. 

1.1826; 1. 1H()9 .T4. 06 WX'M PotJiftalum chloride (KCl) .... 0.1374" 0.1387 

0.0719 I 0.072U 2.07 2. 13 i S4»diuin chlorid«' (NaCl) 2.2466' 2 2428 

1.4271 41.15 1 40. 99 I Sodium Hulphato (NaaSO*) 0.2621 0.2757 

StKlium cailwnate (Na«CH>s) 0. 4940 0. 4834 



0. 1772 i 0. 1864 ! 5. 10 



5.34 



2.98(»2 85.77 I 85.54 
0..~>098 14.23 I 14.46 



Total' 3.4458 



3.4618 



ToUl , 3.4725 1 WAVWi 100.00 100.00 11 

I 



'* 99.23 per cent, accoanteil for in the naniplc fioni 1 r<N>t b<>low aurfacc, and 99.19 per c«nt. in rfmaining aample. 



58 



GEOLOGICAL HISTOKY OF LAKE LAQONTAN. 



tFater o/ Pymmul Lake collated in ^ll^Mf, 1682, at *, north of Anatna liUxnS (rae Flatr IX). 



ssf"' 




OBBlttwofwalM 


"^'wlldfc 


1 


n 

U 




4. MIS 


0.02M 


L17 


0.57 


(>.a§DI) 


O.UMS 


2.59 


2.31 


1,1731 


1,1817 


33. » 


83.82 


D.OTM 


O.OTM 


!,»S 


aw 


I.42M 


l.«12 


«0,*7 




il-im 


0.1650 


S-IS 


5.31 


•■.Mfa 


l.BBIfl 


85. Jl 


tu-sa 


<,.!«« 


a.4l«l 


Ult 


14.14 


n.«7 :,,4e37 


,„o,« 


100.00 



IS 

I- 

'HI 



s»(B10i) j 0.04M 1 

riiMlDiDcvboii>ta(lf(ECOi)... 0.2S00 ! I 

I Calcium rJ>rbnD*M (CaCO.) '0.0447 1 I 

iliiui chloride (KCl) 0. 1474 | I 

n cblaride <H>CI) .. , 2.2411 I : 

tjodluiii nnlphale |NM^) . . . 

1 enTbonite (XmCOi) 0.4738' 



rd Tor In runplefhiDi 1 foot brlolr anrface, anil 100. Ifi pfTf«nt {a 



AU the water aamplea from Pyramid Lake when analyzed contained a 
small quantity of suspended flakes of calcareous and siliceous matter, which 
had separated since the samples were bottled. 

These analyses show much less difierence in the composition of the water 
near the northern and near the southern ends of the lake than was antici- 
pated ; and the examination of top and bottom samples fails to indicate an 
increase in salinity with increase in depth, such as was found by Lartet in 
the case of the Dead Sea.^ The bearing of the present composition of Pyr- 
amid Lake on the interpretation of the history of the ancient lake which 
flooded the same basin will be considered in connection with the chemistry 
of the other lakes of the basin. Standing alone, the analyses of the water 
of the present lake are of geological interest as showing the composition of 
waters that are now depositing calcareous tufa of the same general character 
as that flrst found in Lake Lahontan. 

During our measurements of the depth of the lake the cup at the end 
of our sounding lead seldom failed to bring up a specimen of the bottom. 
From the samples tlm.s obtained we learn that the bottom near shore is usu- 
* EipIoTntioD Gdologique (le Is Her Morte, Paris, 18T7, p. S7S. 




"•"•i 



LAKES OF THE LAHONTAX BASIN. 59 

ally composed of sand or gravel in which the shells of fresh water gastero- 
pods were frequently obtained. At a distance of a few rods from land the 
bottom invariably became muddy, excepting in sheltered bays, where the 
littoral deposits had a greater breadth than when the lake margin was pre- 
cipitous. In all the central portions of the lake the bottom is of fine tena- 
cious mud, either gray in color or intensely black, and having the odor of 
sulphuretted hydrogen The samples of black mud when dried in the open 
air lost their inkiness as w^ell as their odor, and became identical with the 
gray mud occumng in other localities. 

In the southern portion of the lake the water is slightly discolored, and 
is charged with a multitude of shining particles that are rendered visible 
when a ray of light is passed through it. The lack of transparency is appar- 
ently due to the suspended silt brought down by the Truckee River. In the 
northern part of the lake the water becomes wonderfully clear, and at some 
distance from land of a deep blue color. On looking down into the waters 
from the neighboring hills the color appears almost black, or black tinged 
with deep blue. Near shore, especially where the bottom is of white sand, 
the water presents a clear greenish-blue tint, as is the case on nearly all 
lake shores where the bottom is light colored. When thrown into breakers 
by strong winds it exhibits a play of colors that is only rivaled in beauty 
by the surf of the ocean. 

The largest and most attractive islands in the lake are Pyramid and 
Anaho, which rise in its southern portion near the eastern shore. Anaho 
Island, as determined by engineer's level, is t517 feet above the water level 
of 1882, and is surrounded by water from 150 to 300 feet deep. We pre- 
sent an accurate map of it, prepared in August, 1882 (Plate II), from which 
future changes in lake level may be determined. When seen from a dis- 
tance the island presents a convex outline due to the deposition of vast 
amounts of tufa at certain horizons. A broad terrace has been carved all 
around it at an elevation of about 100 feet above the lake, and forms a ped- 
iment for the extremely rugged crags that are piled upon it. The contour 
formed by the water line of this terrace is indicated by the lower of the 
three dotted lines on the map ; the next above marks the water level at the 
dendritic stage ; and the highest of all is the Lahontan beach. This island, 



60 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

although without fresh water, and but scantily clothed with vej^etation, is 
one of the most instructive points about Pyramid Lake, and will well re})ay 
a visit from the geologist or the artist. During the time that Lake Lahontan 
had its greatest extent, Analio Island rose but a few feet above its surface. 

Pyramid Island, as determined by sights with an engineer's level from 
Anaho Island, rises 289 feet above the lake ; the water near its base is from 
150 to 175 feet deep As remarked by Fremont, its regular pyramidal form 
and preci[)itou8 sides give it a striking resemblance to the great pyramids 
of Egypt Its sides are somewhat convex owing to the immense accumu- 
lation of tufa deposited upon them, and are difficult to scale. On the ac- 
companying plate this island is represented as it appears from the neighbor- 
ing shore 

The most picturesque portion of the shores of Pyramid Lake is at the 
northern end, where a rugged cape, known as **The Needles," projects a mile 
or more from the main land, and has near it many small islands of peculiar 
and sometimes fantastic form. This group of spires, domes, and crags ex- 
hibits rock forms of the most rugged description, and furnishes the grandest 
display of tufa in all their varieties that is to be found in the Lahontan basin. 
A general view of this picturesque point is given on the accompanying 
plate, whi(*Ji is sketched from a photograph taken on the lake shore to the 
westward of The Needles. The highest of the spire-like masses, rising 300 
feet above the lake, is shown somewhat in detail in the illustration forming 
Plate XIII. A photograph of one of the islands near The Needles, taken 
from the peninsula, is given on Plate XXXVIII. Plate XXXIX also illus- 
trates the remarkable towers and domes that the tufa deposits here simulate. 

On the northern side of the })eninsula a number of hot springs rise 
from the bottom of the lake and along the base of the tufa crags, and are 
forming a deposit of calcareous tufa beneath the lake surface. This accumu- 
lation is soft and creamy white, and forms a more or less regular layer over 
considerable areas. The hot water of the submerged springs rises from 
many orifices, a number of which have built up tubular chimney-like 
growths 5 or G inches high that sometimes look not unlike mushrooms, 
but always have one or more openings at the top, through which the spring- 
water issues The carbonate of lime is deposited when the hot spring- water 



I 



SUHLAOUSTIIAL SPUING DlirOSlTS. 



Gl 



comes ill contact with tlie colder and more dense watera of the lake A 
few of tile di'|)oslt)s from these springs are represpiited, half natural size in 
the foIIowin<f figure 




Among The Needles tlie rocky ciipes are connected by crescent-shaped 
beaches of clean, creamy sjinds, over which the suimn<>r surf breaks with 
soft nnirmurs. These sands are oolitic in structure, and are formed of con- 
centric hiyers of carbonate of lime which is being deposited n<;ar where 
the warm springs rise in the shalhiw margin uf the lake. In places these 
grains have increased bv continnal accretion until they are a quarter 
of an inch or more ui diameter, and form gravel, or |)isolite, as it 
would be termed by mineralogists In a fen' localities this material lias 
been cemented into a solid rock, and forms an oolitic limestone sufficiently 
compact to receive a polish. No more attractive place can be found for the 
batlier than these secluded coves, with their beaches of pearl-like pebbles, or 
the rockv capes, washed by pellucid waters, that offer tempting leaps to the 
bold diver. The tufa forming The Needles is gray in tone, with a llglil- 
colored band, 10 or 1^ feet broad lit the base, consisting of a coating «)f 
very recent calcareous deposit, similar to that forming the oolitic sands, 
but probably not dependent on spring action. On the cliffs the nucleus 
about which tlie lime crystallised was immovable, and became coated with 
a continuous laver of culciuni carbonate; on the btach the sands were 
washed about by the waves, and grew into little spheres of polished marble. 
A band of recently-formed tufa, like that surrounding the base ot The 



62 GEOLOGICAL HISTORY OF LAKE LAKONTAN. 

Needles, occurs around the borders of all the islands in the lake, and may 
be distinguished at many points on the shores of the mainland. By com- 
paring a photograph of *'The Domes," near Pyramid Island, taken in the 
summer of 1882, with the photograph of the same locality taken in 867, 
as published in the report of the United States Geological Exploration of 
the Fortieth Parallel (Vol. I, Plate XXIII), we learn that the surface of 
Pyramid Lake in the older photograph is 10 or 12 feet higher than when 
the later picture was taken. As this diflFerence in the levels of the lake 
corresponds with the breadth of the band of recently-formed tufa, we are 
led to believe that the deposition of the calcareous deposit took place during 
the recession of the lake thus recorded The shores of Pyramid Lake, like 
those of all the lakes in the lower portions of the Great Basin, are without 
trees or shrubs, and clothed only with a scanty growth of desert vegetation. 
Although the scenery about this lake impresses one with its desolation and 
want of life, yet the rugged mountains surrounding it and the clear, bright 
blue of its waters combine to form a picture of more than ordinary grandeur. 
Like the ocean, its surface appears bright and blue in the sunshine and cold 
and gray in the storm. Even in summer the gales rise suddenly, without 
warning, and sweep down upon the lake with the fury of a tempest Some- 
times within a few moments the lake is changed from a placid mirror to a 
sea of frotliing billows that break on the shore in long lines of foam. The 
suddenness with which the wind changes, and the bleak, inhospitable 
character of the shores, make the navigation of this lake somewhat danger- 
ous, even to experienced boatmen. Many tales of adventure, sometimes 
accompanied by loss of Hfe, are related by those who have experienced the 
sudden storms of this inland sea. 

The lake is abundantly supplied with splendid trout, Salmo purpuratus 
Henshavi^ Lord, and, as stated by Prof. E. D. Cope,^ is also inhabited by 
Leucm oUvaceus, Leucus dimidiatuSj Siphateles Uneahis^ Squalius ffaltice, Chas- 
mistes cKJus, Catostomus Tahoensis; of mollusks, three species — Pompholyx 
effma^ Lea, var. solida^ Dall. ; Pyrgula Nevaden^is^ Stearns ; and Pyrgula 
humerosa, Gould — are living in its waters, and their dead shells occur in 
abundance along the shore. 

^ Proceedings Acad. Nat. Sci. Philadelphia, 1883, p. ir2. 



t 

5 

f - 

t 

I 
I 



LAKES OF THE LAFONTAN BASIN. 



63 



The resemblance of Pyramid Lake to an anii of the sea is enhanced 
by the presence of numerous sea-birds. About The Needles especially one 
sees large numbers of gulls, terns, cormorants, pelicans, together with 
geese, ducks, swans, herons, bitterns, etc. Many of these find convenient 
nesting places in the hollows of the calcareous tufa. During our visit to 
Anaho Island in August, 1882, there were two large pelican "rookeries," 
in each of which there were 600 or 800 young birds. 



WINNEMUCCA IjAKE. 

This, like its sister lake, occupies a long, narrow valley, formed by 
orographic displacement, and is a fair illustration of a lake occupying a 
fault basin. It is 26 miles long, with an average breadth of about 3^ miles, 
the longer axis being due north and south. As in the case of Pyramid 
Lake, its waters are alkaline and brackish. The following analysis by Prof. 
F. W. Clarke is of a sample collected in August, 1882, near the center of 
the lake (at c, Plate IX) and 1 foot below the surface: 



Constitaents. 



I One liter of 
I water con- 
I t a i n 8 in 
grammes — 



Silica (SiO») 

Magnesium (Mg) ■ . . 

Calcium (Ca) 

Sodiam (Na) 

Potassium (K) 

Chlorine (CI) 

Snlpburic aoid (SO4) 



Per cent, in 
total solids. 



0.0275 


0.76 


0.0173 1 


0.48 


0.0196 , 


0.54 


1.2970 ! 


36. 00 


0.0686 


1.90 


1.6934 


47.01 


.1333 


3.70 



Constitaents. 



Silica (SiO?) 

Magnesium carbonate (MgCOi) 
Calcium carbonate (CaCOs^ — 

Potassium chloride (KCl) 

Sodium chloride (NaCl) 

Sodium sulphate (NavSOi) 

Sodiam carbonate (NatCOs) — 



Probable com- 
bination (in 
grammes per 
liter). 



0.0275 
a 0494 
0.0264 
0. 1310 
2.6877 
0.1972 
0.4065 



Carbonic aoid (COa) by difference . 
Total 



3.2567 I 
. 3458 ! 



90.39 
9.61 



3.602o 



100.00 



Total (98.44 per ot accounted for) 



8.5247 



Nearly all of the water that supplies the lake enters at its southern 
end, and consequently causes this portion to be fresher than the northern 
part. As stated while describing the Truckee River, the water supplying 
this lake is a branch of the main stream. The only published account 
known to us of the bifurcation of the Truckee River, so as to supply two 
lakes, is given by Mr. King,'^^ who states that — 

At the time of our lir»t visit to this region, in 1H()7, the river bifurcated ; one half flowed into Pyra- 
mid Lake, and the other thronf;;h a river four or five miles long into Wiunemucca Lake. At that time 



**U. 8. Geological Exploration of the Fortieth Parallel, Vol. L, pp. 505-6. 



64 GEULOGICAL EISTOKY OF LAKE LAHONTAN. 

the level of Pyramid Lako was I?.890 foot above the Hca, aiMl of Wiiiueiiuicca aboat HO feet lower. 
Lati^r, owing to the diBtiirhancc of the balauce between iutlnx aud evaporation already alluded to aa 
expresMiug itself in Utah by Ihe ri^e and expansion of Great Salt Lake, the basin of Pyramid Lake was 
filled np. and a back water overflowed tbo former re<jiou of bifurcation, 8othat now the surplus waters 
all go down the channel into Winnemueca Lake, and that basin is rapidly tilling. 

Between 1*^1)7, (he time of my first visit, aud 1871. the time of ray last visit, the area of Winnemueca 
Lake had nearly doubled, and it has risen from its old altitude about 22 feet, Pyramid Lake in the 
same tilhe having been raised about 9 feet. The outlines as given upon our toi)ographical nuips are 
according to tin* survey of 1H<>7, and form interesting data for future comparison. 

The diftV^rences in elevation between Pyramid and Winnemueca lakes, 
as reported by Mr. King, and as determined by the present survey in 
August, 1882, are as follows: In 1867 Pyramid was 80 feet higher than 
Winnemueca (U. S. Geol. Expl. 40th Parallel, Vol. I, p. 505); in 1872 Pyra- 
mid was 67 feet higher than Winnemueca (U S. Geol. Ex[)l. 40th Parallel, 
Vol I, p. 506); in 1882 Pyramid was 12 feet higher than Winnemueca, as 
determined by engineer's level. 

We know of no accurate means of determining how much each lake 
individually has varied since 1872, but the decrease in the diflFerence of the 
levels of the two lakes is certainl}' due in part to the lowering of the waters 
of Pyramid Lake, as is indicated by recent tufa deposits and lines of bleached 
sea- weed at an elevation of about 12 feet above the present surface of the 
lake. From the data now in hand, providing that all the measurements 
are correct, it is evident that Winnemueca Lake has risen over 40 feet since 
1S72, and over 50 feet since 1867. 

The history of the fluctuations of these lakes is supplemented and en- 
larged by the statements of Mr. George Frazier, who has been familiar 
with the region since 1862 Tn his judgment Winnemueca Lake has risen 
about 40 feet in the last twenty years. In 1862, ihe branch of the Truckee 
Hiver that supplies Winnemueca Lake was so low that a person could cross 
it by stepping from stone to stone, at a point where it is now not less th.an 
25 feet deep. The lake was then confined to the northern extremity of its 
basin, and the stream reached it after meandering through meadow lands 
that are now 15 or 20 feet under water. At that time the channel of the 
stream could be traced along the bottom of the lake for some distance, and 
dead cottonwood trees were standing in the water, showing that the lake 
had previously been much lower. Dead trees standing in Pyramid Lake, 
some distance from the shore, bore similar evidence to the rise of that lake 



.■ < 



-\- 



■■ »' 



« 

'.•*' 



Kr 



\, 



LAKES OP THE LAHONTAN BASIN. 



65 



previous to 1862. This lake, however, is thought by Mr. Frazier to be 
much higher at present than when he first saw it. During the spring and 
summer of I8b8 the Truckee dehveretl more water than usual, and Pyramid 
Lake rose 10 or 15 feet This rise continued throughout the following 
year, and during these two years Pyramid overflowed into Winnemucca 
Lake. The water in the "'slough" at that time was brackish and unfit to 
di-ink. In the summer of 1876 all the water of the Truckee River emptied 
into Winnemucca Lake, its outlet into Pyramid Lake having been closed 
by a gravel bar; but the annual rise of the river the following spring re- 
moved the obstruction. These observations, although not of scientific 
acciii-acy, are yet of value, and have been coufirmed by other people who 
have been acquainted with these lakes for a number of years. 

We may note here that the rise of Pyramid and Winnemucca lakes 
during the last fifteen or twenty years is synchronous with a similar in- 
crease observed in Goose, Horse, and Mono lakes, California; Walker 
and Ruby-lakes, Nevada; Great Salt and Rush lakes, Utah. 

In determining future fluctuations of level in Pyramid and Winne- 
mucca lakes, tlie accompanying map, Plate IX, may be considered as of 
approximate accuracy; the soundings, too, were made with care. Besides 
these data we have determined the elevation of certain points above the 
surface of the lake, which will serve as bench-marks for future measura- 




furtiiiuofthecut Hlioreofl'yratDld Lake, sbawliiK poalrlOD of m«BDred iwcka. 

ments. In the southern end of Pyramid Lake, and to the eastward of the 
Truckee delta, rise a group of tufa crags, indicated on the map by the let- 
ters X, y, z. An enlarged plat of this portion of the lake shore is given in 
the accompanying figure. The height of these crags above the surface of 

MON. £1—5 



66 GEOLOGICAL HISTORY OF LAKE LAHONTAX. 

ft 

the lake, September 9, 188*^, was as follows: x^ 21.0 feet; y, 9.8 feet; ^, 
23.7 feet. 

This record may be increased by adding the following elevations above 
the lake level as determined in September and October, 1882:^ 

Summit of Anabo Island 517 feet 

Summit of ^^ Mushroom Keck," on the north shore of Anaho Island 

(see Plate XIV) 17 feet 3 inches 

Kock to the south of Mushroom Bock (beneath bird on Plate XIV) . 8 feet 5 inches 

Summit of Pyramid Island (Plate XI) 289 feet 

Highest spire among The Needles (Plate XIII) 300 feet 

HUMBOIiDT liAKE. 

Humboldt Lake is but an expansion of the river that supplies it, and 
is held in check by an immense gravel embankment that was thi'own com- 
pletely across the valley by the currents of the former lake, at one time 500 
feet deep at this point. An accurate map of this structure is given on Plate 
XVIII, and a detailed description on page — . As there described, the em- 
bankment has been cut across by the overflow of the lake and the breach 
partially filled during the past few years by an artificial dam, which has 
greatly increased the area of the lake. During the dry season the lake 
seldom overflows and is then the limit of the great drainage system of the 
Humboldt River, but in winter and spring the waters escape southward, 
and spreading out on the desert form Mirage LaKe. Farther southward on 
the northern part of the Carson Desert they again expand and contribute 
to the formation of North Carson Lake. 

In the summer of 1882, Humboldt Lake covered an area of about 20 
square miles, did not oveiflow, and although somewhat alkaline was inhab- 
ited by both fish and mollusks, and was sufiiciently pure for human use. 
The following analysis of its waters by Prof. O. D. Allen, of Yale College, 
is taken from the reports of the United States Geological Exploration of the 
Fortieth Parallel, Vol. II, p 743. 

^ AH these measurements were made with an engineer's level. 



r* 



V 



if 



■«■■ ■ * 

' ■ ■■ •. ' 






V 



^ T 



^. 



.»; 



* 



. ^ 






' *•,■•». 



I ■■ 



c 



. .«■ 



y. 



i; ^■ 






•l - 



■r r 



■ -s 



/€ 






• ■ * ■ 



»' : 



'<*: 



■ ^s -. 



■ . . « «. J" « fir, 



-■ .^^ *• 



I 



I ; 



I I 



LAKES OF THE LAHONTAN BASIN. 



67 



Constituents. 

Specific irravity, 1. 0007. 

Fixed residae in 1,000 parts .. 

Constitaents fonnd in 1 ,000 part« 

Carbonic: acid 

Sulphuric acid 

Phosphoric acid 

Chlorine 

SiUoa 

Magnesia > 

Lime 

Sodium 

Potassium 

Lithia 

Boracic aoid 

Oxygen 



Average. 



0.9015 


0.9045 


0.9030 


0.1065 


0.1075 


0.1070 


0.0257 


0.0248 


0.0253 


0.00060 




0.00069 
0.2952 


0.2954 


0.2049 


0.0320 


0.0330 


0.0325 


0.0281 


0.0268 


0. 0274 


0.0180 


0. 0172 


0. 0176 


0.2786 


0.2788 


0.2785 


0.0612 


0.0605 


0.0609 


trace. 




trace, 
trace. 


trace. 






0.84509 






0.04273 




0.88782 



There is probably a loss of carbonic aeid. 



The theoretical combination of bases and acids would give- 



Carbonato of soda 

Sulphate of soda 

Chloride of sodium 

Chlorido of potassium . 

Carbonate of lime 

Carbonate of magnesia 

SQica 

Phosphoric acid 



0.24944 
0.04498 
0.89571 
0. 11617 
0.03143 
0. 05768 
0.03250 
0.00069 



Less carbonic acid added to the 
amount found 



0.92860 



04254 



0.88606 



A series of soundings made in Humboldt Lake, in July, 1882, gave a 
nearly uniform depth of 12 feet for the central part. Near the western 
shore quite extensive mud-banks rise a few feet above the surface and nearly 
divide the lake; westward of these the water is still more shallow than in 
the main body. The lake is being rapidly filled by the silt from the Hum- 
boldt River, and is destined to early extinction. 

Owing to the orographic structure of the valley it occupies, the east- 
ern shore of the Humboldt Lake is bordered by a precipitous cliff of dis- 
placement, the western shore is low and marshy, in places covered with a 
saline efiiorescence. A sample of the incrustation from the surface of the 



68 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

desert near Brown's Station was found by Mr. R. W. Woodward to have the 
following composition :^^ 



CoD8titaent«. , Percent. 



Soluble in water \ 27. 71 

Chloride of sodium | 49.87 

Snlpbato of soda 2U. 88 

Sesqnicarbonate of soda I 18. 16 

Borate of soda IL 80 



I 



100.00 



NORTH CARSON LAKE. 

This lake is situated on the northern part of the Carson Desert (see 
Plate VII) and receives its waters from both the Humboldt and the Carson 
rivers. Having no outlet, the waters flowing into it have been supposed to 
sink, and for this reason it is generally spoken of as the "Humboldt and 
Carson Sink." As this term is based on an error, we have used the name 
"North Carson Lake" instead. 

During the winter and spring it receives a considerable supply of water 
from both the Humboldt and Carson rivers, and becomes a shallow playa- 
lake, between 20 and 25 miles in length, by 14 miles in breadth. In unu- 
sually arid summers the water supply fails, and the lake evaporates to dry- 
ness. As desiccation becomes more intense the salts impregnating the lake- 
beds are brought to the surface and form an efflorescence several inches in 
thickness. 

This was the case when the Carson Desert was visited by the writer in 
October, 1881. The lake had then wholly evaporated, leaving a broad mud- 
plain covered in places with a white alkaline crust that looked like patches 
of snow. 

SOUTH CARSON LAKE. 

Situated on the southern border of the Carson Desert lies South Car- 
son Lake. This, like the larger lake to the northward, is a playa-lake and 
occupies a very shallow depression in the lake-beds flooring the desert. 
Like other lakes of its class, it has indefinite boundaries and varies in size 

»U. 8. Geological Exploration of the Fortieth Parallel, Vol. II, p. 744. 



LAKES OF THE LAHOlS^TAN BASIN. 69 

and deptli with the alternation of seasons. In 1882 its area was about 40 
square miles, with a depth of four feet throughout its central portion. Its 
waters are alkaline, and contain 1.4725 grammes of solids in solution to the 
liter; of which 0.2135 gramme is silica, as reported by Prof F. W. Clarke 
from a partial analysis of a sample collected in October, 1863. 

The lake is supplied almost entirel}^ by the Carson River and usually 
overflows through a slough into North Carson Lake.^* 

The low muddy shores are strewed with the dead shells of Anodonta 
Plnnorbis, Limncea, etc., but, so far as known, no mollusks are now living 
in the lake. 

WAIiKER liAKE. 

The southern extremity of the Lahontan basin is occupied by Walker 
Lake, which, next to Pyramid Lake, is the most picturesque and attractive 
of the desert lakes in the Lahontan basin. 

A correct outline of the lake, as it existed in 1882, is given on Plate 
XV. As may be gathered from the map, the lake is 25.6 miles in its longer, 
or north and south axis, and has an average width of between 4.5 and 5 
miles. Its area is 95 square miles As on the map of Pyramid Lake, the 
actual soundings are given in figures, and the somewhat conjectural topog- 
raphy of the bottom is represented by dotted contour lines. . Over a large 
area in the central and western portions it has a remarkably uniform depth 
of 224 feet; but as a rule the depth increases as one approaches the west- 
ern shore, which is overshadowed by rugged mountains. The bottom 
throughout the central portions is composed of fine tenacious mud, which 
in many places is black in color, and has the odor of hydrogen sulphide. 
Coarser deposits, consisting of sand and gravel, mingled with the empty 
shells of Pyrgulaj Pompholyx, etc., were found only in the immediate neigh- 
borhood of the shore. No mollusks were found living in the lake; but the 
conditions of environment being so similar to what has been observed in 
Pyramid Lake, it is thought that a more careful search would show that 
Walker Lake is also inhabited by a few species. • Analyses of the water, 
collected in September, 1882, one foot and 215 feet below the surface 

'* See aple, pajje 44. 



70 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



where the depth was 224 feet, as ahowD on the accompanying map, are re- 
ported by Prof. F. W. Clarke as followa: 












-'1 


CoutilueDU. 


1" 


SI ^:i ISi j 




II 


ni|ii, 


SUlo (SlOt) 






1 


M-Soe^lum (Hg) 






;:;:■ "\ 




0.026T 

o.ssn 


B-nm 


:^'^\ 


Sodium (N.) 








Tr»w. Tram. 


Cbleritie (Cl» 




a sflti- 




o-fii-yj 


,.«HS 


W.l» . aiB" 






Z.MKI 


j.uWI 


Bi, »a 1 w Ts I 




0.4895 


...7S. 


18..7! lft->T 


TiM.1 


asm 


-••'• 


.«..00|1<».«0 



Protwblc •Mtm- 
preuriL In 



SlllM(RIOt} . 
MBgDHiam oi 
CbIcIdiii citrlM 



rboute (UgCOil . 



W Sodium ohloride 



(KlCl) |0.9Gei 0.MS8 

it8(N«iSO.) «.7803 a75«0 

■le(NHCOi) ' 0.!>1S7 S33S 



Total ■2.S1SS I 



'BS.Wpsr ceut. •ceoDDtvd for. t>7.Wp«rM 

Ab in the caae of the otlier lakes of the Great Basin, situated at an ele- 
vation of less than 5,000 feet, the shores of Walker Lake are totally lacking 
in arboreal vegetation except at the river mouth, and are clothed only with 
desert shrubs. At the northern end, and following the immediate shores of 
the Walker River for many miles, are luxuriant cottonwood groves, to- 
gether with willow-banks and meadow-lands. 

At the northern end, the river is building out a low delta of fine silt, 
and remnants of similar deltas, at higher levels, may be seen as one follows 
up the river. A change in the level of the lake is recorded by dead trees 
standing in the water, which show that it has risen at least four or five feet 
in recent years. 

The waters at a distance from the river mouth are of a clear deep blue, 
chan^ng to a bright green tint near the shore, as in Pyramid Lake. They 
are charged with saline matter to such an extent that carbonate of lime is 
now being deposited. The calcareous tufa now forming cements the gravel 
and sands of the shore into compact strata or forms rosette -shaped masses, 
with isolated pebbles for nuclei. 






1 




■^'■J*!* 





,KE. NEVADA 



I ' 



I . 



r 



t 



■ ( 



' II 



LAKES OF THE LAHONTAN BASIN. 71 

in the study of the recent and fossil lakes of the Far West it is fre- 
quently desirable to know the present rate of evaporation, and the charac- 
ter of the seasonal and secular variations in precipitation that are taking 
place. Attempts have been made to determine the rate of evaporation by 
experimenting with artificial evaporating pans, but owing to the difficulty 
of imitating the conditions of nature, these observations have been of little 
value. Gauges have been established in Great Salt Lake, and accurate 
records of its annual and secular fluctuations have been secured for a num- 
ber of years, but in this instance tlje variations of the lake are influenced by 
irrigation, and the sources of supply for the waters of the lake are too numer- 
ous to be definitely measured. Of all tiie lakes of the Far West with which 
we are acquainted, excepting Abert Lake, Oregon, the most favorable for 
determining the questions indicated above is Walker Lake. As this lake 
receives its entire supply from a single source and is without outlet, the rate 
of evaporation from a large water surface could be determined with great 
accuracy. Observations intended to show the secular variations in precip- 
itation would be more difficult because the waters of Walker River are 
largely used for irrigation. 

IjAKE tahob. 

As Lake Tahoe is the grandest of the Sierra Nevada lakes, and the 
largest that discharged into Lake Lahontan, we insert a brief account of it, 
compiled principally from the investigations of Prof John Le Conte, of the 
University of Califomia.^^ 

The lake is situated in latitude 39° N., and lies part in California and 
part in Nevada, at an elevation of 6,247 feet, as determined by railroad 
surveys. Its drainage area, including the lake surface, is about 500 square 
miles. The water surface is 2L6 miles long from north to south, with an 
extreme breadth of 12 miles; its area being between 192 and 195 square 
miles. Its outlet is the Truckee River, which leaves the lake through a 
magnificent gorge, at a point on its northwestern shore. 

3: «( Physical Studies of Lake Tahoe/' published iu the Free Press and the Mining and Scientifio 
I'resj* of San Francisco, during 18>*0 and 1H81. Reprinted in the Overland Monthly for November and 
IVcmmIm r. l-H{, and .laniiaiv, lhH4. 



72 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



Soundings made by Professor Le Conte, beginning at the northern 
end, near the "Lake House," and advancing along the longer axis of the 
lake directly north towards the '*Hot Springs," at the northern end, give 
depths of from 900 to 1,645 feet 

Between the 11th and the 18th of August, 1873, Professor Le Conte 
made a large number of temperature measurements at different depths in 
the lake, an abstract of which is here copied : 



No. 



Depth in 
feet. 



Depth in Temperature: Temperatare: 
meters. l^shr. Cent. 



1 (surface). 

2 

3 

4 

5 

6 

7 

8 (bottom) . 
9 

10 

11 (bottom). 
12 

13 (bottom) . 

14 (bottom) . 



50 
100 
150 
200 
250 
300 
330 
400 
480 
500 
600 
772 
1,506 



15.24 

30.48 

45.72 

60.96 

76.20 

91.44 

100.58 

121.92 

146. 30 

152.40 

182.88 

235.30 

459.02 



67 

63 

55 

50 

48 

47 

46 

45.5 

45 

44.6 

44 

43 

41 

39.2 



19.44 

17.22 

12.78 

10.00 

8.89 

8.33 

7.78 

7.50 

7.22 

6.94 

6.67 

6.11 

5.00 

4.00 



Professor Le Conte's paper also contains many valuable observations 
on the transparency and color of the lake water, and on rhythmic variations 
of level. An analysis of the water of Lake Tahoe lias already been 
given on page 42. 

Besides Lake Tahoe, there was another lake among the mountains of 
Northern California during Quaternary times which was tributary to Lake 
Lahontan. This was a comparatively shallow water body that occupied 
the basin now known as the Madeline Plains. A small stream from Horse 
Lake Valley joined that draining the Madeline Plains; as did also the 
waters escaping from Eagle Lake, which, without evidence to the con- 
trary, we may consider to have discharged, then as now, through beds 
of gravel beneath a lava coulde. 



SODA liAKES, NEAR RAGTOWN, NEVADA. 

On the Carson Desert, about 2 miles northeast of Ragtovvn, are two 
circular depressions that are partially filled with strongly alkaline waters 
and known as the Soda Lakes or Ragtown Ponds By reference to the 
accompanying map (Plate XVI), on which the contour lines are drawn at 
intervals of 20 feet, it will be seen that the lakes occupy deep depressions 
in low cones. The larger lake is 268.5 acres in area, and the smaller is a 
pond of variable size.^ The form of the larger depression is still farther 
illustrated by the cross-section given at the bottom of the plate, which has 
been constructed from actual measurements with an engineer's level and a 
sounding line. The rim of the larger lake in its highest part rises 80 feet 
above the surrounding desert, and is 165 feet higher than the surface of 
the lake which it incloses. The outer slope of the cone is gentle and merges 
almost imperceptibly with the desert surface; but the inner slope is abrupt 
and at times approaches the perpendicular. A series of careful soundings 
gives 147 feet as the greatest depth of the lake. The total depth of the 
depression is therefore 312 feet, and its bottom is 232 feet lower than the 
general surface of the desert near at hand. 

The walls encircling the lake exhibit well exposed sections of stratified 
lapilli, mingled with an abundance of angular grains, kernels, and masses 
of basalt, some of which are 2 and 3 feet in diameter and scoriaceous, 
especially in the interior. Mingled with this angular and rough material 
is a great quantity of fine dust-like lapilli, and some rounded and worn 
pebbles of rhyolite. Interstratified with the lapilli occur marly lake-beds 
containing fresh-water shells and dendritic tufa, as is indicated in the 
accompanied generalized section of the crater walls (Plate XVII, Fig. A). 
Both the lapfUi and the lake-beds are evenly stratified, and exhibit diverse 
dips. On the interior of the larger crater, on the south side, the dip is 
towards the lake at an angle of about 30°. On the east side the stratifi- 
cation appears quite horizontal, but may, perhaps, be inclined away from 

^Tho smaller lake, when the accompanying map was made, bad been so cbang&d by excavation 
and the construction of evaporating vats that its original form had been destroyed. lU surface is 20 
feet higher than the larger lake, and 05 feet below the general desert snrface. The highest point on 
the crater riai is 80 feet above the bottom of the depression. 

73 



74 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

the crater; near the surface of the lake there are two planes of iinconfomi- 
ability, as well as a number of small faults. In the crater walls on the 
opposite side of the lake a number of displacements may be seen, as indi- 
cated in Fig. E, Plate XVII. 

The form of the cones and the nature of the material of which thev are 
composed leave no doubt that these are crater-rings, i. e., low cones of erup- 
tion containing large craters. The evidence sustaining this conclusion is 
abundant In the stratified beds of yellowish lapflli, which are always an- 
gular and sometimes as fine as dust, are many fragments of basalt, rhyo- 
lite, and masses of hardened lake-beds,^ that are evidently ejected frag- 
ments that have been dropped from a considerable height to the positions 
which they now occupy. The strata of lapilli beneath these *' bombs" are 
bent down, as shown in the accompanying sketch (Figs. B, C, and D, Plate 
XVII) the disturbance being visible for fi or 8 inches below the included 
rock. The strata of loose cinders covering the inclosed fragments are 
horizontal and undisturbed. That the cones were not formed during a 
single eruption, but have a long and complicated history, and are perhaps 
sublacustrine in their origin, is shown by the alternation of ejected and 
sedimentary materials in the crater walls. 

From the presence of fossiliferous lacustral clays in the midst of lapflli, 
it seems evident that volcanic eruption was interrupted by periods during 
which the lake covered the craters. The presence of dendritic tufa in the 
midst of the section proves that the volcano was active both before and after 
the dendritic stage of Lake Lahontan. The wall of the larger lake is some- 
what open on the south side, while the western rim has been prolonged 
southward (see Plate XVI) in such a manner as to suggest that the erupted 
material was in part removed by currents at the time it was ejected and 
deposited in the form of an embankment, connecting with the crater rim. 

The hypothesis that the craters were formed by the action of extremely 
powerful sublacustrine springs, as advanced by King,^* would not account 
for the nature of the material forming the crater walls, nor the presence of 

'^The rhyolite pebbles and fragments of lacastral sediments thrown out by this volcano were evi- 
dently derived from the superficial strata through which it opened a passage. The basalt, on the other 
hand was empted in a semi-fused condition and formed slaggy masses on cooling. 

»U. 8. Geological Exploration of the Fortieth Parallel, Vol. I, p. 512. 



^Rs 







■s 



N 



\ 



7' 



LAKES OF THE LAHONTAN BASIN. 75 

the numerous volcanic bombs that depress the strata on which thev rest. 
If the cavities owed their origin to springs of very great magnitude nsing in 
tJie bottom of Lake Lahonb\n, it is evident that the out-flowing waters would 
have cut channels of overflow when the lake evaporated to a horizon below 
the rim of unconsolidated material that surrounded them ; but the crater 
walls are now continuous and unbroken by stream channels. On the other 
hand, had the springs become extinct before the evaporation of the lake the 
cavities they formerly occupied would be buried beneath lake-beds. This, 
as our observations show, is not the case, but both the inner and outer 
surfaces of the cones are free from lake sediments The last addition of 
lapflli to the walls of the crater must have been of post-Lahontan date. 

The least diameter of the larger crater at the water surface is 'A, 1 68, 
and its greater 4,224 feet. Its area, as stated on a previous page, is 268.5 
acres. A sublacustral spring of these dimensions, rising with sufficient 
force to carry blocks of basalt 1 or 2 feet in diameter to the height of 
1 50 feet, would be a phenomenon without parallel. That the lakes occupy 
extinct Craters is recognized by Mr. Arnold Hague in his description of the 
Carson Desert.'^*' 

There are no streams either tributary to or draining these lakes ; their 
total water supply, excepting the small amount derived from direct precipi- 
tation, is supplied from subterranean sources. Around the immediate shores 
of the larger lake there are a number of fresh-water springs; the largest of 
these is situated on the northern border of the basin, and issues from a small 
fault at an elevation of about 1 5 feet above the water surface. As the lake, 
bv aneroid measurements, is 50 feet below the level of the Caisson River at 
its nearest point, we may safely look to this stream as the probable source of 
the water supply which reaches the craters by percolating through the inter- 
vening marls and lapflli deposits. The bottom of the lake, as determined 
by many soundings, is a continuation of the slope of the inner walls of the 
crater, excepting that the conical form has been modified by shore action and 
sedimentation, which has resulted in the formation of the terrace about the 
present water margin. In the northern part of the lake a reef of rock pro- 
jects above the surface, and soundings show that this is continuous from 

^ U. S. Geological Exploration Fortieth Parallel, Vol. II, p. 746. 



76 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

shore to shore, thus indicating that two craters are combined in the forma- 
tion of the present depression. 

The bottom, as shown by the samples obtained by the cup at the end 
of our sounding lead, is a fine tenacious black mud having a strong odor of 
sulphuretted hydrogen. When exposed to the air for some time this mate- 
rial loses its inky color and shows itself to be of the same nature as the fine 
dust-like laplUi that form a large part of the crater walls. The organic 
matter impregnating these sediments is evidently derived from the millions 
of brine shrimps (Artemia gracilis) and the larvae of black flies that swarm in 
the dense alkaline waters. 

Near the shore the rock and pebbles, as well as bits of organic matter 
are coated with beautiful crystals of gaylussite which form about any solid 
nucleus that chances to be available. The crystals are white, with trans- 
parent edges, monoclinic in form, and thin in the direction of the orthodiag- 
onal, as illustrated by Figure 607, Dana's System of Mineralogy, 5th edition. 
The small island in the northern part of the lake is completely coated with 
gaylussite crystals and trona. An analysis of a crystal of gay-lussite from 
this locality by Prof. O. D. Allen gave the following composition : ^ 

Lime 19. 19 

Soda : 19.95 

Oarbonic acid 29. 55 

Water 31.05 

Sulphuric acid Trace. 

ChloriDe Trace. 

iDSoluble residue 0. 20 

99.94 

Trona also occurs along the shore of the lake up to an elevation of i or 
12 feet, and not unfrequently contains casts of the larval cases of a fly which 
now lives in the lake in immense numbers. An analysis of a sample of 
trona from this locality, by Prof. O. D Allen is here copied.^ 

^ U. S. Geological Exploration of the Fortieth Parallel, Vol. II, p. 749. 
'•U. S. Qeologioal Exploration of the Fortieth ParaUel, Vol. II, p. 748. 



-. Imgnlarly InmiiiWril lapOtl. 

. lAtnlastedtnarloDpUlnluslBpUII, 

Imgiilarly lunlnotrd lupilli. 

Regnlnrly Inmitinli'il lupUli. irllU cjcct»1 rrauiiii^ntt of 
b«aal( and iturl. 














\'^,cv,i'- avrn "d 



ir/ jivOf.', iM. 



J. a ttuBKl, C«Bl<vUt 



SECTIONS OF THE CRATER WALLS INCI QSING THE SODA LAKES, NEVADA. 



LAKES OF THE LAHONTAN BASIN. 



77 



Soda 40.56 

CarbODic acid 30. 86 

Sulpliuric acid 0. 73 

Chlorine 0.98 

Water 19. 90 

Insolable reBldue 0. 80 

99.82 

Oxygen equivalent to chlorine 0.32 



99.60 

"The deposit is thus nearly a pure trona, or sesquicarbonate of soda, 
mixed with small quantities of suljihate of soda and common sah It con- 
tains also traces of pliosphoric and boracic acids. The insoluble residue 
consists of fine sand and carbonate of lime." 

Samples of water collected in September, 1882, in the central portion 
of the lake, at the depths of 1 foot and 100 feet, have been analyzed by Dr. 
T. M. Chatard, who reports their composition as follows: 






■ g£ -i gi 
Jl Ij 11 



BiitcBiaiOi) 

Hainmiii'D lUgl 

PoUUliitn (K) 

ChlnrimKCD - 

8nti>haricaiM<l(SOi) 

HonclDRiTiddttOi) 

Carbonir acid ICOi) by rlttTsnit 
Tom] 

■irtbeexceMo/COi 
from 1 foot bcluw Iha aorfioe; 



I" 


P 


P 


w 


a.»u4 


0.310 


(l,2t 


D,a5| 


0.370 


O.CTO 


fl.ja 




S.flM 


iS70 


2.01 


LIS 


am 


*4,b:ii 


38.83 


.I-M 










12.1W0 


13, IM) 


10. M 




0,814 


0K7 


n,!S 


0-W 


107. «M 


ift.i. zer 


in, 78 


"'ii 


i!.Mao 


17,-, 1.M 


100. «u 


l«» 



8ilH«(SI0,) 

Mameiliim urbonalr (UkCOi) 

Pouidam chloride (KCII 

Sodlnm chloride (NaCI) . ,., | 

Sodlnn. boraW (XiiiBtO.) 

Snllum curbnnBte INhCOil ... 



unoiml nqiilml fur NaiCO. b 

JUlC^ = !3,64 
NiiHC())= 4.SB2 



1B.4M 

0,417 
34. MO 

~i».iiio 



Dulated aa HallUOt. vc will bsve Id the Mmple 



n l«> KaiCOi = e: 

NaCOi = H 

I NilUCOi= K 



39 



78 GEOLOGICAL HISTORY OF LAKL: LAFIONTAN. 

A water sample collected from the south side of the lake in August, 
1867, and analyzed by Prof. 0. D. Allen, had a specific quantity of 1.0975, 
and gave a fixed residue of 114.7 parts per thousand, and on spectroscopic 
examination was found to contain lithia in addition to the elements sriven in 
the above analyses/ 

In obtaining carbonate of soda from the waters of the larger lake two 
methods are in use. One is known as the **cold weather" and the other as 
the ** warm weather" process. In the former the water of the lake is con- 
ducted into vats along its shore, and has a density of about 12° of Beaume's 
areometer As it evaporates beneath the heat of the summer sun its density 
increases until it approaches 30° B. At this point more water is added from 
the lake. This process is continued until cold weather approaches; the vats 
are then so adjusted as to have a density approaching 30° B. The lowering 
of the temperature on the approach of winter causes sodium carbonate and 
sodium sulphate to be precipitated at the bottom of the vats in a hard 
crystalline layer, which, when removed to the drying sheds, crumbles 
to a fine white powder. The "soda" formed by this process contains about 
equal portions of sulphate and carbonate, as shown by the following anal- 
ysis by Dr. F. W. Taylor of a sample of the material as it is sent to the 
market: 

Per oeut. 

Silica 0.449 

Iron and alumiDum . Oil 

Calcium sulphate 038 

Magnesium sulphate 040 

Sodium chloride 2. 193 

Sodium sulphate 49. 437 

Sodium carbonate 40. 714 

Water 7. 118 

100.000 

While concentrating the waters in the soda vats during the summer, if 
the density increases beyond about 30° B., carbonate of soda and sulphate of 
soda are precipitated, and, if concentration continues, is soon followed by the 
deposition of common salt. In this process the water is conducted from vat 
to vat, becoming gradually concentrated as it progresses. When in the last 

^ • U. 8. Geological Exploration of the Fortieth Parallel, Vol. II, p. 747. 



SODA INDUSTRY. 79 

of the series it has reached the desired density, sodium carbonate, together 
with sodium sulphate, is deposited. The mother liquor is afterward returned 
to the lake. The soda thus obtained is called ** summer soda," and has 
about the composition given in the above analysis, as is indicated by qual- 
itative tests. The vats in which the evaporation is conducted are formed 
by levees built along the shallow border of the lake, and are usually about 
80 feet long by 50 feet broad; the water when evaporation commences is 
usually from 12 to 14 inches deep. (Plate XVI.) 

When the waters of the lake are evaporated until a density of about 
15° B. is reached, they assume a reddish tint, which increases as the con- 
centration is carried forward, until at 30° B. they become of a bright cherry- 
red color. Chemical tests show that this color is not due to the presence of 
manganese or iron, but is probably produced by organic substances. 

The manufacture of soda at the larger lake was commenced in 1875, 
and is yet in its experimental stage, although two or three hundred tons of 
impure soda carbonate have been produced. The smaller lake when first 
discovered is reported to have been dry, and presented the appearance of 
an ordinary mud-playa. Excavations carried to the depth of about 25 feet 
have shown that the material filling the basin is composed of layers of soda 
salts, separated by strata of dust and mud. As the layers of soda in these 
beds have the character of the ** summer soda" now formed in the vats, it 
is evident that the crater has served as a natural evaporating pan, in which 
the water accumulated during the wet season was entirely evaporated before 
the dry season had passed. 

For the manufacture of soda in this basin, vats have been excavated in 
the material composing its bottom. They are filled by water seeping from 
its sides, which, as it enters the vats, has a density of from 10° to 15° B. 
Concentration is carried on until the carbonate of soda begins to crystallize, 
when a new supply of brine is added, and the process carried forward until 
cold weather sets in, when an abundant crop of beautiful soda crystals is 
formed during the first cold nights of autumn. After all the soda is pre- 
cipitated that a lowering of temperature will produce, the mother liquor is 
conducted back into lower depressions, and allowed to leach through the 
soda-bearing strata once more The crust of soda obtained at the bottom 



80 GEOLOGICAL HISTORY OF LAKE LA^ONTA^^ 

of the vats is usually about 10 inches thick and shows two divisions, the 
upper layer, or " winter soda," being the more crystalline. The salt thus 
obtained is removed to drying sheds, where it loses its excess of water, at 
the same time crumbling to a fine powder, and is then ready for the market. 
A sample of this material was found on qualitative examination to consist 
principally of sodium carbonate, together with considerable quantities of 
chloride and sulphate of soda, and traces of phosphoric and boracic acid 
and potash. 

The manufacture of soda in the smaller pond lias been carried on for 
about eighteen years, with an annual production of between four and five 
hundred tons, as I am informed by Mr. B. F. Gray, the present superin- 
tendent. 

The walls of the smaller crater are of the same nature as those that 
surround the larger lake, and exhibit sections of stratified tuff containing 
ejected blocks of basalt that depress the strata on which they rest. An 
illustration of the smaller Soda Lake will be found on Plate XXII, Vol. II, 
and of the larger lake on Plate XXVI of Vol. I, of the reports of the 
U. S. Geological Exploration of the Fortieth Parallel. 

The mineral matter now dissolved in the water of the Soda Lakes is 
unquestionably derived from the springs that supply them, and has been 
dissolved from the lacustral beds and lapflli deposits through which thoir 
waters percolate during their subterranean passage. 

The data given on Plate XVI enable one to calculate approximately 
the volume of the larger of the Soda Lakes; and from the analyses of its 
waters that have been made we can determine the quantity of the various 
salts it contains. Making these calculations for the salts of greatest economic 
impoii;ance, we find that the lake contains nearly 428,000 tons of sodium 
carbonate; sodium sulphate amounts to nearly four-fifths of this quantity; 
while the sodium chloride is somewhat less than three times as great. The 
total of all salts dissolved in the lake is in the neighborhood of two million 
tons. 



PliAYA-IiAKES AND PI.AYA8. 

The name "playa-lake" has been applied to inclosed water bodies of dry 
climates which have little depth and frequently evaporate to dryness, leaving 
mud-plains, or playas. In the typical examples found throughout the Great 
Basin, their waters are somewhat alkaline and saline, and almost always 
turbid with fine silt, and, probably, chemical precipitates. This material is 
retained in suspension not only because the shallow lakes are frequently 
agitated to the bottom by the wind, but, also, for the reason that in waters 
containing alkaline salts tlie precipitation of suspended matter is greatly 
retarded. Lakes of this class exhibit great variety, and are the most irregu- 
lar of water bodies. In many instances they hold their integrity for a num- 
ber of years, and only evaporate to dryness during exceptionally arid seasons. 
Again, desiccation is apparently the normal condition, and the basins are 
only flooded during times of unusual humidity. Many lakes of this class 
exist only dunng the humid season, and are dry throughout the summer. 
In the spring and fall, as already mentioned in describing the general fea- 
tures of the Great Basin, they appear with every storm that gathers and 
vanish when the heavens are again bright. Their outlines consequently 
fluctuate with the humidity of the season, and, owing to the extreme shal- 
lowness of their basins, a variation of an inch or two in depth may make 
a difference of many square miles in area. 

Examples of the more permanent playa-lakes of the Lahontan basin 
are furnished by Honey -Lake and tlie lakes of the Carson Desert. Another, 
of less permanence, on the Black Rock Desert, has been noticed on page 10. 
The positions of others, some of which are many miles in extent during the 
winter, but disappear completely when the breath of summer touches them, 
are indicated on the accompanying pocket-map. Examples might be 
multiplied, and the curious effects that these ephemeral lakes exert on the 
scenery of arid lands might be dwelt upon, but this would perhaps carry 
us beyond their geological interest. 

The lakes described above are commonly uninhabited by fish, but 
frequently afford a congenial abode for mollusks, especially for the Limnseidae 
and allied forms. 

MON. XI— 6 81 



82 GEOLOGICAL HISTORY OF LAKE LAHOXTAN. 

The water reaching playa-lakes is commonly derived from the surface 
drainage of the basins in which they occur; the larger ones, however, are 
supplied by streams more or less permanent. The sediment contributed to 
lakes of this description is commonly in a state of minute subdivision, and 
when derived from the surrounding surface is rich in saline matter. When 
evaporation takes place both the suspended and dissolved matter is deposited 
and forms a peculiar light-colored saline clay, which, when desiccation is 
complete, forms a smooth mud-plain, or play a. 

The mud-plains originating in the manner described above are char- 
acterized by the evenness of their surfaces and their light creamy-yellow 
color, which is independent of the nature of the surrounding rocks. These 
deposits have the same characteristics and apparently about the same com- 
position whether sun-ounded by sedimentary rhyolites or basaltic rocks. 
In area they vary from a fraction of an acre up to many square miles. 
They are entirely destitute of vegetation, and are in fact the only absolute 
deserts in this country. During the rainy season they are rendered soft 
and impassable, and very frequently covered with water, as mentioned in 
describing a playa-lake, but with the advance of summer they lose their 
moisture and become so completely desiccated beneath the intense heat of 
the summer's sun that they resemble a pavement of cream-colored marble, 
which, on the broader deserts, stretches away to the horizon without a shrub 
or spear of grass to break the monotony of the glossy surface. Owing to 
the contraction of the mud on drying a play a becomes broken by a vast 
system of intersecting *^sun cracks," which frequently cover the surface with 
an intricate network of narrow fissures. While the mud is soft it sometimes 
becomes impressed with the foot-prints of animals and rippled by the winds^ 
thus receiving markings that are usually considered characteristic of shores. 

Typical examples of playas of broad extent occur in the Lahontan 
basin, on the Black Rock, Smoke Creek, and Carson deserts; others of less 
size are met with in various minor basins, as has been indicated in describ- 
ing playa-lakes. 

The scenery on the larger playas is peculiar, and usually desolate in 
the extreme, but yet is not without its charms. In crossing these wastes^ 
the traveler may ride for many miles over a perfectly level floor, with an 



MIRAGES ON THE DESERTS. 



83 



unbroken sky-line before him, and not an object in sight to cast a shadow 
on the ocean-like ex*panse. Mirasres may be seen every day on these heated 
deserts. Similar optical illusions give strange fanciful forms to the mount- 
ains, and sometimes transfigure them beyond all recognition. At such 
times a pack-train crossing the desert a few miles distant frequently appears 
like some strange caravan of grotesque beasts fording a shallow lake, the 
shores of which advance as one rides away. The monotony of midday on the 
desert is thus broken by delusive forms that are ever changing, and suggest 
a thousand fancies which divert the attention from the fatigues of the jour- 
ney. The cool evenings and mornings in these arid regions, when the pur- 
ple shadows of distant mountains are thrown across the plain, have a charm 
that is unknown beneath more humid skies. The profound stillness of the 
night in these solitudes is always impressive. 

When the heat of summer drives every drop of moisture from these 
deserts a white saline efflorescence appears, which is formed by the crys- 
tallization of various salts brought to the surface in solution by the action 
of capillary attraction, and left as the water that dissolved them is evap- 
orated. Incrustations of this nature sometimes cover areas many miles in 
extent, especially along the borders of the playas, and render the surface 
as dazzling as if covered by snow. 

An analysis of a typical specimen of playa mud from the southern part 
of the Carson Desert is reported by Dr. F. W. Taylor, as follows: 

Portion soluble in water 15.16 per cent. 



CoDstitnents. 



Silica 

Iron BPAqaioxide 

Alaniina ■ 

Magnesium carbonate 
Calcium carbonate . . . 

So<lium carbonate 

Sodium sulphate 

Sodium chloride 

"Water (by difference) 



Soluble 
portion. 



Per cent 

14.05 
2.37 
2.17 
2.90 
0.79 

14.36 
4.28 

53.16 
6.92 

100.00 



Constituents. 



Silica 

Iron sesquioxide. 

Alumina 

Lime(CaO) 

Magnesia (MgO) 

Soda 

Potassa 

Carbonic acid 

Water 



Insoluble 
portion. 




84 GEOLOGICAL niSTOKY OF LAKE LAHONTAN. 

An examination of a sample from another playa gave less than 3 per 
cent, soluble in water, consisting principally of sodium carbonate, calcium 
carbonate, and common salt 

It is not to be expected that all deposits of this character would have 
even approximately the same composition, but the conclusion arrived at in 
the field; that the)" are the result of both mechanical and chemical processes, 
is strengthened by the analyses that have been made. In some instances 
easily soluble salts form a large percentage of the deposit, which then 
becomes a salt-field, a bed of gypsum, or is largely composed of other simi- 
lar salts. At times these deposits become covered with mechanical sedi- 
ments, and perhaps buried so deeply that they are not again dissolved when 
the basin is reoccupied by a lake. All stages in this process, which, in fact, 
is the closing chapter in the history of many lakes, may be observed in the 
arid region of the Far West. 

Playas in which the mechanical deposits greatly predominate are the 
most common, and may be studied in a large number of the desert- valleys 
of Utah and Nevada. Examples of salt-playas are numerous, especially 
in Southern Nevada, where they are of economic importance, and, besides 
common salt, frequently contain large quantities of sodium sulphate and 
carbonate, borax, etc. In some instances the lower portions of earthy 
playas are saturated with brine — as is the case in Diamond Valley, Nevada — 
which, when raised to the surface and evaporated, is capable of suppljnng 
an almost unlimited quantity of salt. One of the most instructive playas 
in the Great Basin is situated in Utah, a few miles southward of Fillmore. 
In this instance the water entering the basin and partially flooding it during 
the rainy seasons is probably charged with calcium sulphate in excess of 
all other salts, and on evaporating leaves a deposit of crystallized gypsum, 
or selenite, which is now approximately 12 square miles in extent, and has 
been penetrated to the depth of 6 feet without revealing its entire thick- 
ness. The salts more soluble than gypsum, which must have been 
deposited by the waters covering the playa at various times, have appa- 
rently been flooded out by an overflow of the basin, thus leaving the sele- 
nite in a remarkably pure condition. The small crystals of selenite swept 
from the surface of the deposit by the wind have been accumulated in im- 



SALT DEPOSITS OF INCLOSED BASINS. 85 

inense dunes, especially along the northern border of the playa, and have 
nearly buried a rhyoh'tic butte beneath snow white drifts, thus acquiring 
for it the local name of the *' White Mountain." 

A stratification of the various salts found in playas in the order of their 
solubility, as commonly occurs from the slow evaporation of brines, is not 
usual, for the reason, apparently, that they owe their accumulation to repeated 
desiccations. In some instances, however, as at Rhode's salt marsh in Ne- 
vada, the more soluble salts are gathered most abundantly in the central 
part of the basin. 

A study of the playas of the Far West renders it evident that saline 
deposits of great extent may result in tlie manner described above, and 
sustains the suggestion that beds of rock-salt, gypsum, etc., found in various 
geological formations may have been accumulated in interior basins by the 
evaporation of ordinary surface waters, and are not in all cases, as fre- 
quently inferred, the result of the evaporation of isolated bodies of sea- 
water. 

Besides the playas proper, the formation and characteristics of which 
we have sketched, there are other desert areas in the Far West that are 
frequently designated by the same name, but which are of a somewhat 
difierent nature. These are mud-plains left by the evaporation of large 
lakes, and composed of ordinary lake sediments. Deserts of this nature 
are in many instances nearly as desolate as the true playas. Their borders 
are commonly poorly defined, being more or less covered with shrubs; 
their surfaces, too, are commonly uneven and irregular. In substance, they 
are usually composed of tenacious greenish clay of the same character as 
the sediments now forming in many large lakes. Usually the deserts of 
this character occupy nearly the entire breadth of an ancient lake-bed, 
and are overlaid by playas proper in their lowest depressions. In a deep 
section of such a playa the light-colored saline clays, of which they are 
almost invariably composed, would be found to pass into the more tena- 
cious and darker clays beneath. The strata at the base of such a section 
were deposited in a deep lake of broad extent, while the playa-beds proper 
are the record of frequent desiccations. 



86 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

The freshening of lakes by complete evaporation is one of the most 
interesting results of the processes we have been tracing. Perhaps the 
strongest proof that the burial of desiccation products beneath earthy sedi- 
ments is competent to convert a lake from a saline to a fresh condition is 
furnished by a number of the existing lakes of Nevada and Oregon, which 
are either fresh to the taste, or else hold but a fraction of 1 per cent, of 
saline matter in solution, but occur in comparatively broad drainage-basins 
that have not overflowed since the beginning of the Quaternary. This 
is illustrated especially by the present condition of the lakes of the Lahon- 
tan basin, as will be shown in treating the chemistry of the former lake 
(postea, page 229). 



CHAPTER IV. 



PHYSICAL HISTORY OF LAKE LAHONTAN. 

Section 1.— SHORE PHENOMENA IN GENERAL. 

The examination of the shores of recent and fossil lakes has shown 
that there are a number of characteristic topographic features, resulting 
from the action of waves and currents, which are of geological interest, and 
frequently enable one to determine much of the history of a lake that has 
passed away. The dynamics of lake waters may be studied in any exist- 
ing lake, but the topography of shores is best seen in lake basins that have 
been emptied of their waters at a recent date. 

If we stand on a shelving lake shore during a gale that is blowing 
landward, and watch the waves breaking on the beach, it will be noticed 
that they apparently become accelerated on entering shallow water, and, 
as their crests break into foam, thej^ rush up the beach or shore-terrace, 
carrying stones and pebbles with them. As each wave retires we may hear 
the sharp rattle of this material, even above the roar of the waters, as it rolls 
dnd slides down the beach, only to be caught up by the next innish, and 
the process repeated again and again. Outside the line of foam fringing 
the shore the water is frequently discolored, perhaps for several rods, by 
suspended sediment derived from the comminution of shore debris ; farther 
lakeward the waves are clear and blue, or perhaps streaked with long lines 
of foam. The most superficial observations tend to assure us that vast 
quantities of stones, pebbles, sand, and silt are constantly carried up and 
down lake beaches and become rounded and smoothed by the process. 
This conclusion is also sustained by the worn appearance of the d^is on 

87 



88 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

every shore. A little attention also enables one to ascertain that the beach 
material greatly assists the waves in cutting away the coast so as to form 
terraces and sea-clifFs, and is subsequently utilized in building bars and 
embankments. Tlie modifications of lake shores due to chemical action 
need not receive attention at this time. 

The principal features entering into sliore topography are terraces, 
sea-cliffs, bars, embankments, and deltas. These, as will be shown below, 
result from the action of waves and currents on the shores that confine 
them, and differ so widely from the topographic forms produced by sub- 
aerial erosion and other geological agencies that the nature of their origin 
may be determined at a glance. 

TERRACES. 

The most characteristic forms resulting directly from wave action are 
sloping terraces bounded by a steep scarp, termed a sea-cliff, on the land- 
ward margin, and a second scarp, less abrupt, on the lakeward border. 
These forms are illustrated in the following diagram, which represents the 
profile of a lake shore so carved by waves as to form a cut -terrace and sea- 
cliff. The line ab represents the original slope of the shore before its mod- 
ification by waves; ac the profile of the sloping terrace ; and cb the sea-cliff. 



LA/C£ \p}ff^AOe^ 



Fio. 8.— Ideal profile of a cat-torrace. 

In the desiccated lake basins of Utah and Nevada terraces of this nature 
frequently occur that are hundreds of feet in breadth and overshadowed by 
cliffs which at times are a thousand feet high. 

The material derived from the formation of a cut-teiTace at first encum- 
bers the shelf formed, but is soon removed by the waves and currents and 
its place supplied by fresh debris. The finest of the waste from the land is 
carried lakeward by the undertow and finally deposited as lacustral beds^ 



THE WORK OF WAVES AND CUllREXTS. 89 

portions less finely comminuted fall on the outer slopes of the terrace and 
serve to broaden it. The coarsest of all the shore debris usually remains 
on the terrace and is swept along by the currents until it finds a resting- 
place in some embankment or wave-built bar. The portion falling on the 
outer margin of the terrace is frequently consolidated by the precipitation 
of calcium carbonate in its interstices, thus forming a conglomerate, which 
adds to the breadth of the structure. In this manner a terrace may become 
in part a work of destruction and in part a work of construction, as indi- 
cated in the following diagram, which represents a cut-terrace, as in the last 
figure, with the addition of an accumulation of debris on its outer slope. 



^^ lA^r S VRFA CE 




Fio. 9. — Ideal profile of a cut-and-built terrace. 



Observations have shown that this is the most characteristic form of 
lake terrace, and illustrates the fact that the action of waves and currents 
in modifying shores may be divided into erosion and deposition, or the 
processes of destruction and construction. 

8EA-CL.IFF8. 

The steep scarps rising above teiTaces are termed sea-cliffs, whether 
fonned on lake or ocean shores. They occur especially where the borders 
of a lake are abrupt; but when the bluffs approach the perpendicular and 
form cliffs with deeply submerged bases, the action of the waves in carving 
ten'aces is reduced to a minimum, for tlie reason that the shore debris falls 
into deep water beyond the reach of the waves and can no longer be used 
as a tool in cutting away the land. On the other hand, sea-cliffs are sel- 
dom formed when the slope of the beach is very gentle. In such localities 
the waves lose their force before reaching the land, and deposition rather 
than erosion takes place. Sea-cliffs are most pronounced in rocks of hete- 
rogeneous composition, w^hich are easily eroded, but yet sufficiently durable 
to stand in perpendicular escarpments. 



90 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



BARS. 

In the illustrations given above the eflfects of waves that result from 
winds blowing directly on-shore are alone considered. When the wind blows 
obliquely to the beach we have another modification of wave action. Cur- 
rents are established in each instance by the friction of the wind on the 
water, but in the first they are at right angles to the beach and return lake- 
wards as an undertow; in the second case, however, i. e., when the wind 
blows obliquely to the land, the currents formed move more or less nearly 
parallel with the shore, as may be illustrated along any lake margin by 
placing floats in the water or by watching the movements of the shore-drift 
It will require but little attention to assure one that during a gale strong 
currents are thus established along lake margins, which in some respects 
are similar to the flow of rivers. They carry with them a band of shore- 
drift, consisting of sand, gravel, bowlders, etc., the width of which depends 
mainly on the slope of the sliore and the character of the material moved. 
As in tl>e flow of streams, the transported material is carried partly in sus- 
pension and partly by rolling along the bottom. The upward wave move- 
ments tend to lift the stones and the onward movement to carry them for- 
ward. When the force of the current is checked the coarser debris is first 
deposited and the finer transported to greater distances. The movement of 
such current-borne streams of debris along a lake shore necessitates friction, 
which results in the comminution of the debris itself and the abrasion of 
the base of the sea-clifi* against which it impinges. Shore currents are even 
more powerful than on-shore waves as agents of erosion, but their distinc- 
tive property is the power to transport shore-drift. In this manner the 
debris supplied by the sapping of sea-cliffs is removed and formed into new 
structures at the same time that it causes the detachment of fresh material 
from the shore, thus supplying fresh tools with the aid of which the waves 
remodel their boundaries. 

Shore currents are usually strongest at some distance from the actual 
lake niargin. In some instances this distance amounts to several rods or 
perhaps half a mile. As the maximum transportation takes place where the 
current is most rapid, the result is the formation of a ridge of gravel in the 
path of the current. Deposits of this nature are molded by the waves 



/ 



TOPOGBAPHT OF LAKE SHOBE8. 



91 



into long, narrow, level-topped ridges, with rounded crests, which follow 
the broader curves but not the minor irregularities of lake shores. They are 
composed of water-worn debris which has been assorted by currents, and 
when exposed in cross-section they present an iiregular anticlinal of depo- 
sition. Gravel ridges of this nature have received the name of harrier-bars. 

The altitude of the horizontal crest of a barrier bar is determined by 
the storm limit of the waves and cuirents that built it Each such structure 
therefore furnishes a record of the horizon of tlie water's surface in which 
it was formed. Should a lake vary in level, it is evident that barrier bars 
may be constructed at many different altitudes. In the desiccated lake 
basins of Utah and Nevada bars of this nature frequently occur in con- 
centric and symmetrically curved ridges, which may be followed for miles 
and sometimes furnish natural highways of a most excellent character. 

An ideal plat of an arm of an ancient lake in which barrier bars were 
formed at three different levels is given in the following figure. Below 




Fio. 10.— IdpdiiUt uiilMCtloDllliutnliDg tbetorniiUoDorbkniarbm. 

the sketch is a section through the valley on the line xp, in which the level 
of the surface of the lake at the time the various bars were formed is indi- 
cated by dotted lines. 



92 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



The conditions most favorable for the formation of barrier bars obtain 
when shelving shores occur adjacent to steep banks wliere sea-cliflFs are 
forming; in such instances the debris derived from the sapping of the sea- 
cliff is swept along by shore currents, and furnishes the material for works 
of construction. 

Sometimes a current is deflected from the shore and returns to it at 
another point. In this manner a looped bar inclosing a lagoon is formed. 
The lakeward portion of such a bar sometimes forms a definite angle; the 
structure then becomes V-shaped, and is known as V-bar. Bars with this 
peculiar form are not uncommon, and sometimes obtain great magnitude. 
It frequently appears as if structures of this nature had been begun in a 
rising lake, and that the forms of the shore deposits first made were 
retained and carried upwards as the lake rose, by the addition of fresh 
material to their surfaces. Barrier bars present other variations, some of 
which will be noted in the succeeding pages, which may frequently be 
seen in process of formation on the shores of existing lakes. 

Bars of another character are also formed along lake margins, at some 
distance from the land, which agree in many ways with true barrier bars, 
but differ in being composed of homogeneous, fine material, usually sand, 
and in not reaching the lake surface. 

The character of structures of this nature mav be studied about the 
shores of Lake Michigan, where they can be traced continuously for hun- 
dreds of miles. There are usually two, but occasionally three, distinct sand 
ridges; the first being about 200 feet from the land, the second 75 or 100 
feet beyond the first, and the third, when present, about as far from the 
second as the second is from tlie first. Soundings on these ridges show 
that the first has about 8 feet of water over it, and the second usually 
about 12; between, the depth is from 10 to 14 feet. From many com- 
manding points, as the summit of Sleeping Bear Bluff, for example, these 
submerged ridges may be traced distinctly for many miles. They follow 
all the main curves of the shore, without changing their character or having 
their continuity broken. They occur in bays as well as about the bases 
of promontories, and are always composed of clean homogeneous sand, 



■I 



TOPOGRAPHY OF LAKE SHORES. 93 

although the adjacent beach may be composed of gravel and boulders. 
They are not shore ridges submerged by a rise of the lake, for the reason 
that they are in harmony witli existing conditions, and are not being 
eroded or becoming covered with lacustral sediments. 

In bars of this character the fine debris arising from the comminution 
of shore drift appears to be accumulated in ridges along the line where 
the undertow loses its force; the distance of these lines from the land 
being determined by the force of the storms that carried the waters shore- 
ward. This is only a suggested explanation, however, as the complete 
history of these structnres has not been determined. * 

EMBANKMENTS. 

The combined action of waves and currents along shores of moderate 
slope results, as we have seen, in the formation of cut terraces, sea-clifi*s, 
built terraces, and barrier bars. When the shore becomes steep or any 
abrupt change in its direction takes place, as when the mouth of a bay is 
reached or a promontory projects from the shore, the current does not 
follow the sinuosities of the land but continues its course, and, on entering 
deeper water, loses its power of transportation and deposits its load. 
Fresh material is carried along in a more or less continuous stream by 
the shore current and added to that previously deposited, thus forming 
a subaqueous embankment. This process is continued until the deposit is 
raised to the level of the barrier bar or terrace, as the case may be, along 
which the current-borne debris is carried. This process continuing, the 
embankment increases in length but not in height; its crest, like that of a 
barrier bar, has its height determined by the horizon of the lake surface. 
It is evident from their mode of foraiation that embankments are but pro- 
longations of built terraces and barrier bars; in fact one form merges into 
the other in such a manner that it is not always possible to determine in 
which list a given structure should be placed. 

The formation of embankments will, perhaps, be rendered more intelli- 
gible by referring to the accompanying topographic sketch, in which a por- 



94 



GEOLOLICAL DISTORT OF LAKE LAUOXTAN. 



tion of a gently sloping lake margin adjacent to a bay is represented. The 
current in sweeping along the shelving shore in the direction indicated by 




Fia. 11.— Idt'al).latellmt 



the arrow, will carry with it a narrow band of shore drift; when the en- 
trance to tlie hay is reached the direction of the cnrrent is hut little changed; 
it consequently enters deeper waters where its velocity is checked and its 
load of debris deposited. Fresh material continues to be swept along the 
shore terrace and is added to that already accumulated until a long, narrow, 
level-topped embankment is built up. Current-formed structures of this 
nature have the character of a railroad embankment, and sometimes grow 
to be miles in length and perhaps several hundred feet high. Should the 
conditions represented in the sketch continue long enougli, it is evident tliat 
the bay will eventually bo cut off from the lake and form a lagoon ; in such 
an instance it is frequently convenient to speak of the structure as a bay- 
embankment. In case the bay chances to be at the mouth of a stream, the 
embankment may become breached by the outflowing waters and repaired 
again by the currents, thus complicating the stratification of the deposit. 

Embankments, like barrier bars, when exposed in cross section present 
a more or less perfect anticlinal structure due to the mode of their deposi- 
tion. When buried beneatli subsequent deposits, as lacustral beds, for ex- 
ample, and dissected by erosion, they sometimes simulate a true anticlinal 
formed by the folding of the strata ; an instance of this nature is illustrated, 
on Plate XXV. 

Simple embankments, like that shown in the above illustration, are usu- 
ally either straight or but slightly curved, and end at the distal extremity in 
a semicircular scarp the slope of which depends on tiie angle of stabihty in 
water of the material of which the structure is composed. Beyond the end 
of the embankment sand-banks are commonly formed by the subsidence of 



TOPOGRAPUY OF LAKE SUORES. 



95 



the finer particles carried along by the current and held in suspension for 
some time after the coarser material has been deposited ; as the structure is 
prolonged this fine d/bris becomes buried beneath the gravel and stones 
composing the major part of the embankment, and many times becomes 
folded and crumpled owing to the weight of the superimposed mass. 

The action of waves and currents in forming embankments is subject 
to a multitude of variations dependent on the topography of the shores, on 
the character of the material moved, on changes in the direction of winds 
and currents, and on many other conditions. As may be imagined, the 
resultant forms are equally diverse. Should a lake be also subject to great 
fluctuations of level, the structure and grouping of the embankments will be 
still more complicated. When a lake rises, new embankments and built- 
terraces are formed above older ones ; when it falls, previously formed 
structures are cut away and remodeled into new forms. In the first instance, 
a line of division or an unconformability will mark the junction of the older 
and the newer deposits ; such an example is shown in cross section at a in the 
following figure, which represents contiguous built-terraces of diff'erent date: 
the altered conditions may also be recorded by changes in the character of 
the material of which the embankments are formed. In the second instance^ 




Fig. 12. — Diagrams illastratiDg the relative age of gravel terraces and embankments. 

i e.j when the lower structure is formed subsequently to tlie upper, the un- 
conformity is of a different nature as is illustrated by section b ; in an 
instance of this nature the scarp of tlie older structure is quite commonly 
somewhat modified by erosion. When cuiTent-built embankments of dif- 
ferent dates are not contiguous, as represented at c, their relative age cannot 
be determined in the same manner as in the previous examples. 

Sometimes a current in sweeping past a promontory will build embank- 
ments tangent to it, which become curved or sickle-shaped at their free ex- 
tremities, as is illustrated on Plate XIX ; again, such embankments may 
curve abruptly at the end so as to resemble the letter J, and are conven- 



I 

• I 

I 
I 



96 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

iently designated as J -bars. Other modifications of gravel-built structures 
will be noticed in the descriptions of the shores of Lake Lahontan which 
follow. 

Water at rest having no power to erode, it is evident that lakes modify 
their shores but little during calm weather ; it is when storms are raging 
that the potency of waves and currents reaches a maximum, and the greater 
part of terrace cutting and bar building takes place. The level of the high- 
est water line as recorded by works of construction, is the storm level ; in 
some instances this is several feet above the normal lake surface, for the rea- 
son that the water is raised to an abnormal height along a shore against which 
a gale is blowing. The topography of a coast may cause the storm waves to 
reach a higher level in some portions than in others, as, for example, whero 
a funnel-shaped bay opens out into a broad lake. In such an instance the 
water will be driven into the bay during on-shore storms and forced to a 
greater height than on a more open coast. For these reasons the higliesk 
beach-lines of a lake at various points are not always in the same plane ; a 
fact that should be borne in mind while measuring the depth of fossil lakes 
and in studying the eflfects of orographic movement. 

DELTAS, 

The general forms of the fan-shaped accumulations of gravel, sand, and 
silt deposited about the mouths of streams which enter still water, are too 
well known to require a detailed description. 

When a stream bringing silt and sand in suspension and rolling peb • 
bles and larger rock masses along its bed debouches into still water, iU 
momentum is checked and the greater part of its load is deposited. When 
the structure thus begun is undisturbed by currents it is built out equallj- 
in all directions from the mouth of the stream and thus acquires a semi • 
circular or fan-shaped topographic form. When a high-grade stream enters 
a valley it commonly deposits a heap of debris about the point of discharge, 
which has received the name of an alluvial cone; a delta may be consid 
ered as an alluvial cone that has been formed with its base below water. 
The part of a delta that is above the reach of the waves has the irregulai* 
structure characteristic of alluvial deposits, but the submerged portion 



DELTA STRUCTURE. 97 

acquires a more or less well-defined oblique stratification, which may be 
called a "delta structure." During the building of a delta the stream mean- 
ders over all parts of its surface that are not submerged, and, in iiregular 
succession, discharges at all points of its periphery; in this manner the 
stream-borue debris is carried to all points on the edge of the deposit and 
allowed to roll down the submerged slope. The strata thus formed are in- 
clined, the amount of their inclination depending upon the angle of stability 
in water of the material deposited. Observation has shown that the slope 
of a delta seai-p commonly is from 20 to 25 degrees. The fine sand and 
mud held in suspension is carried farther than the stones and gravel, and 
is deposited about the base of the delta scarp, decreasing in quantity and 
becoming finer the farther it is can-ied from the point of discharge The 
stream-borne silt thus tends to build up a secondary cone outside the base 
of the main delta, which, on its outer margin, merges with the lacustral 
sediments deposited in the central portion of the lalie. In the growth of a 
delta the scarp of coarse debris is gradually advanced on all sides and con- 
sequently overplaces the secondary cone at its base; this added weight fre- 
quently causes the fine sediment to be crumpled into folds and perhaps 
broken by small faults. 

A delta deposited at the mouth of a high-grade stream will have three 
well marked divisions, as shown in the following diagram: 




At the top is an alluvial cone (a) of unassorted material, resting on (b) 
a deposit of obliquely stratified gravel, which in turn is built out over a 
secondary cone (ca) of sand and silt. As a delta grows, a becomes thick- 
ened, and is built out over b, which at the same time is carried forward over 
c. In this manner the characteristic tripartite structure of deltas originates. 
In low-grade streams, which all long rivers necessarilj' are, the material 
MON. XI 7 



I : 



98 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

transported to their mouths is fine silt, and in their deltas the divisions de- 
scribed above are obscure and indeterminate. 

A fluctuation of lake level during the formation of deltas produces 
even greater modifications in their forms and structure than the same change 
of conditions would in the nature of current-formed embankments. When 
the waters of a lake rise and submerge a delta, a new one is at once com 
menced and carried forward in the same manner as the first, which it may 
eventually bury so completely that only a deep section would reveal its 
presence. In some ancient deltas that have been dissected by erosion a 
stratum of lacustral sediments is found separating two delta deposits. In 
such an instance the included sheet of fine material is thickest near the 
outer margin of the structure; the formation of the higher delta and the 
deposition of the fine sediments took place at the same time, the latter being 
finally overplaced by the former. The lowering of a lake causes its tribu- 
tary streams to erode channels through their previously formed deltas and * 
to commence the building of new ones, either in the gap thus formed, or 
altogether below the former structure. In some instances in the Bonne- 
ville and the Mono basins this action was carried forward at a number of 
successive stages until a series of small deltas were formed, each starting in 
the channel cut through its predecessor In the formation of deltas, as in 
the construction of terraces and embankments, one of the most important 
conditions requisite for the production of typical examples on a large scale 
is permanence of lake level. The finest deltas are formed in lakes that 
maintain a constant horizon for a considerable time and receive the influx 
of high-grade streams which are abundantly loaded with debris. 

In the above sketch attention has only been given to the modifications 
of lake shores and tideless seas ; the action of the waves, currents and tides 
of the ocean receiving no consideration, because they are foreign to the 
scope of the present essay. 

REC APIT UL. ATION. 

Cut terraces are shelves carved in the shores of lakes by the action of 
waves and currents; they are bounded on both their shoreward and lake- 
\yard margins by steeper slopes; the former inclines upward and forms a 



i 



RfiSUMfi OF SHORE TOPOGRAPHY. 99 

sea-cliff, the latter slopes downward and forms a terrace scarp. Their upper 
limit is a horizontal line marking the level of the water at the time they 
were formed; their surfaces slope gently lake ward. 

Built terraces are shelves of debris formed along shores and are usually 
adjoined to or combined with cut terraces. As in the previous instance, they 
are limited on their lakeward borders by terrace-scarps, and may or may not 
occur at the bases of sea-cliffs. Their shoreward margins are horizontal. 

Sea- cliffs are scarps formed by the erosion of cut terraces ;. theii* bases 
are horizontal and coincide with the upper limit of terraces. 

Barrier bars are ridges usually composed of water- worn gravel, depos- 
ited by cun-ents in shallow water at some distance from land. Their crests 
are horizontal, and mark the storm limit of the waves and currents that 
built them. In cross- section they exhibit anticlinals of deposition. Aber- 
rant forms are V-bars, J -bars, looped bars, etc. 

Embankments are deposits formed by the transportation of shore drift 
along terraces and barrier bars, of which they are continuations, to locali« 
ties where the water deepens. Like built terraces and barrier bars, they 
are composed of water- worn (Ubris, but are frequently of great size; their 
tops are horizontal, and in cross-section they exhibit anticlinals of deposition. 

Deltas are accumulations of stream-borne dohris deposited about the 
mouths of streams that debouch into still water; topographically they are 
semicircular or fan-shaped, and, when seen in radial section, exhibit a tri- 
partite structure. 

Since the present chapter was written, a graphic and comprehensive 
summary of lake shore phenomena has been published by Mr. Gilbert in the 
Fifth Annual Report of the United States Geological Survey, to which the 
reader is referred for a more complete discussion of the geological effects 
of waves and currents than is contained in the present sketcL 



Section 2.— SHORE PHENOMENA OF LAKE LAHONTAN. 

In considering the question of outlet in a previous chapter, it was shown 
that the shores of Lake Lahontan are unbroken by a channel of overflow. 
It was therefore an inclosed lake, and, like others of its class, mxxst have 



I.' 
h: 
I I 



100 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

been subject to repeated fluctuations of level. That such was its history is 
also evident from the multitude of ten-aces still remaining as records of its 
former changes. The Lahontan water-lines are lacking in strength as com- 
pared, for example, with those of Lake Bonneville, the reason being in part, 
evidently, that the ancient lake margins were precipitous throughout a large 
portion of their extent, and the water-surface was greatly broken by islands 
and headlands which must have retarded the force of the waves and cur- 
rents; but the main reason why the old shore Hues are poorly defined is 
that the lake surface was not held at any definite horizon for a considerable 
time. The records of wave action still remaining are sufficiently distinct, 
however, to be easily traced, except on some gently-sloping shores where 
the waters were shallow, and at the heads of deep narrow bays where all 
shore phenomena are frequently absent. In the Lahontan basin, as in all 
fossil lakes, the elements of shore topography to which we turn for the 
history of the ancient water-body are terraces, sea-clifiB, bars, embank- 
ments, deltas, etc. 

TERRACES AN*D SEA-CLIKFS. 

The most common of the records inscribed on the borders of the La- 
liontan basin are cut terraces. These may be traced throughout a very 
large portion of the basin, but are most distinct oh the borders of the larger 
deserts. About the southern margin of the Carson Desert the ancient lake 
was limited by mountains of soft, volcanic rock, which yielded easily to 
both wave action and subaerial erosion. The result is a group of Gothic- 
like mountains rising from a broad, horizontally scored base. The contrast 
between rain sculpture and wave-sculpture is here well marked. 

In traveling over the Central Pacific Railroad between Golconda and 
Wadsworth, one is seldom out of sight of the long horizontal lines drawn 
by the waves of the ancient lake on the shores that confined them. Rec- 
ords of the same character may be traced continuously about the borders 
of the Black Rock and Smoke Creek deserts, and are strongly defined along 
the bases of the mountains overlooking Pyramid and Winnemucca lakes. 
They are again plainly legible on the steep slopes bordering Walker Lake, 
as may be observed by the traveler over the Carson and Colorado Railroad. 



/ 



TERRACES AND SEA CLIFFS. 101 

The highest of these numerous shore lines we have named the "Lahon- 
tan Beach," as it records the highest water stage of the former lake. Its 
elevation above the sea, as shown by lines of level connecting with the Cen- 
tral Pacific Railroad surveys, is 4,343 feet at Mill City, and from 4,418 to 
4,427 feet at the lower end of Humboldt Lake.*^ Barometric measurements 
of the altitude of Pvramid Lake, for which I am indebted to Messrs. J. S. 
Diller and M. B. Kerr,*^ determine its 1882 level to have been 3,783 feet above 
the sea. The Lahontan beach in the vicinity of the lake, as measured by 
several lines of leveling, is 530 feet above its 1882 level, and therefore 4,313 
feet above the sea. The altitude of the surface of the former lake, as deter- 
mined by Clarence King, was 4,388 feet.*^ These results, together with 
many measurements with the aneroid barometer and by angulation, show 
that the old shore lines are not now horizontal, owing to the orographic 
movement that has taken place since their formation, as will be described in 
Chapter X. What their original horizon may have been is not now suscept- 
ible of accurate determination. An average of the various measurements 
that have been made of the present elevation of the Lahontan beach gives 
4,378 feet, which is the nearest approximation we can make to its original 
altitude. 

Besides the Lahontan beach there are three other water-lines of suffi- 
cient importance in the history of the lake to deserve special designation. 
One of these is a strongly defined terrace, 30 feet below the Lahontan beach, 
and at the upper limit of a calcareous deposit, precipitated from the waters 
of the ancient lake, which we have named '* Lithoid Tufa"; we therefore 
call this the ** Lithoid Terrace." Its elevation is 500 feet above the 1882 
level of Pyramid Lake. 

Another chemical deposit, known as " Dendritic Tufa," occurs in great 
quantities in the same basin, and at its upper limit is bounded by a water- 
line, usually but poorly defined, which we name the '* Dendritic Terrace.'^ 
Its elevation is 320 feet above the datum plain just mentioned. 

^oSee protilo in Plate XVIII. 

^^Its elevation was deteriiiiut-d by barometric readings at Keno and at the lake surface in Jane, 
1884, au<l gave a difference of level of 715.5 feet. The elevation of Reno, as determined by the Cen- 
tral Pacific Railroad snrveys, is 4,497 feet. 

-♦^U. S. Geological Exploration of the Fortieth Parallel, Vol. I, p. 507. 



1 1 
I . 



.■l 






102 



GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



Between the dendritic terrace and the surface of Pyramid Lake there 

is a broad platform, which is the strongest and best defined of all the La- 

hontan water-lines. It marks the upper limit of a third variety of tufa, 

known as '^Thinolite"; we call it, therefore, the '*Thinolite Terrace." Its 

elevation is about 110 feet above the level of Pvramid Lake in 1882. This 

terrace has been found to extend entirely around the valleys occupied by 

Pyramid and Winnemucca lakes, and may also be followed, though with 

less certainty, along the borders of Black Rock, Smoke Creek, and Careon 
deserts. 

The terraces we have nanied, together with the present level of Pyra- 
mid Lake, furnish four definite horizons that will be found convenient refer- 
ence plains in tracing the Quaternary history of the basin. It is only at 
exceptional localities, however, that these terraces can be followed for any 
considerable distance, and at only a few points could a sequence like the 
one shown below be obtained from actual measurements. Our diagram is 
a generalized profile of the Lahontan shores. 




Feet. 

Lahoutan boach 53«» 

Litboid torrac« r>ua 

Dondritic l«^i race 320 

Thinolile terrace 110 

Surface of Pyramid Lake (1882).... 



Fig. 14.<— Geoeralized profile of Lahontan shorcH. 

The relative age of the various water-Hnes shown in the diagram will 
be discussed in connection when the chemical history of the lake is consid- 
ered. 

The highest terrace of all, the Lahontan, is an inconspicuous feature 
in itself, but it is important as forming the boundary between subaerial and 
subaqueous sculpture on the sides of the valleys. It usually appears as a 



i 



TEERACES AND SEA-CLIFFS. 



103 



terrace of conetruction a few feet wide, resting on the broad lithoid terrace 
30 feet below. Where the sliore records are unusually well displayed, as 
along the western niargm of Pyramid Lake and on the south side of the 
Carson Desert, the lithoid terrace sometimes has a width of 200 or 30" 
feet. Resting on it we sometimes find two built terraces of gravel and rolled 
fttones, tlie water-line of one being the highest of all the shore records; 
the second is intermediate between the Lahontan beach and the lithoid 
terrace. This arrangement is illustrated in the accompanying diagram, which 
exhibits a generalized proJilc of the sliore : 




The line oi represents the original slope of the mountain side before it 
was modified by the waves of the lake. The lithoid terrace cd was first 
formed, the outer edge being built of detritus. The magnitude and persist- 
ence of this terrace indicate that the water stood for a long time at a nearly 
constant level, allowing the waves to carve out a broad shelf from the solid 
rock. As we sliall see further on, the terrace became coated with calcareous 
tufa, and its gravel was cemented into a conglomerate. At some later 
period in the history of the lake the water rose and built the two small 
embankments, or terraces, that rest upon it, but it remained at these hori- 
zons only a comparatively short time. 

Besides the more definite and strongly marked terraces to which we 
have given names, there are a large number of less deeply engraved line.-: 
on nearly every portion of the former shore. Each of these scorings, as 
we well know, is the record of a pause in the fluctuations of the water sur- 
face ; collectively they indicate numerous changes in the lake level. The 
obscurity and want of strength in many of tlie terraces is no doubt due in 
a great measure to the fact that the slopes on which they are traced have 



104 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

been brought within the reach of wave action many times. In this way 
the records first made have been erased or obscured by subsequent additions. 

One of the best localities in the basin for the observation of ancient 
lake- margins is at Terrace Point, near the northern end of Pyramid Lake.*® 
The water-lines at this locality are drawn at nearly equal intervals, and are 
approximately of the same strength. Even at a distance of several miles 
they continue to form a conspicuous and striking feature in the scenery of the 
region. These terraces are the result of both the destructive and constructive 
action of waves and currents, and are largely composed of basaltic debris 
mingled with worn and rounded fragments of the different varieties of tufa 
that sheath the interior of the basin. The presence of tufa in the terraces ren- 
ders it evident that they were formed subsequent to the deposition of the 
main tufa deposits, and, therefore, at least in part, belong to a very recent 
chapter in the history of Lake Lahontan. These facts will receive further 
consideration in the discussion of the chemistry of the tufas. 

The topography of terraced shores is well illustrated on Anaho Island, 
Pyramid Lake, a map of which forms Plate X. The broad bench formed 
by the lithoid terrace extends completely about the island and forms the base 
for the tufa-coated crags that are apparently piled in huge pyramids upon 
it. At an elevation of 320 feet above the lake surface the poorly defined 
dendritic terrace may be seen, and nearly at the top of the island is a faint 
line marking the position of the Lahontan beach. At the time when the 
ancient lake reached its greatest extension, Anaho Island stood but 15 or 
20 feet above its surface, and during severe storms must have been com- 
pletely buried by the dash of the waves. The modifications of topography 
produced by terraces may also be seen on the Marble Buttes at the south- 
em end of Pyramid Lake, which at one time formed a group of small 
islands in Lake Lahontan ; and, again, about the shores of Humboldt Lake, 
a portion of which are shown in Plate XVIII. 

Although the terraces in the Lahontan basin are sufiiciently distinct to 
enable one to trace the outline of the ancient lake with accuracy, yet they 
are by no means so well defined as the similar records made by the waters 
of Lake Bonneville. In the former instance we have the result of the action 



^'SefPlac IX. 



THE WORK OF WAVES AND CURRENTS. 105 

of the waves and currents in an inclosed lake, the surface of which must 
have fluctuated with the seasons, and become of broad extent during long 
periods of more than usual humidity, only to contract again and perhaps 
be divided into separate water bodies with the return of arid conditions. 
Hence the comparative indefiniteness of its water lines. In the case of the 
ancient Utah lake the horizons of the most strongly defined terraces were 
determined by overflow ; the water surface was thus maintained at a con- 
stant level for long periods, and the shore phenomena at these favored stages 
became the grandest that have yet been studied. 

BARS AND EMBANKMENTS. 

The deposits in the Lahontan basin that owe their origin wholly to the 
constructive action of waves and currents are far more important and in- 
structive than the associated terraces, and are deserving of the most careful 
attention. Accumulations of gravel in the form of bars and embankments 
occur at many points along the ancient shores which we are studying, but in 
many cases these structures are indefinite or complicated, and their bearing 
on the history of the former lake is difficuh to trace. We have therefore 
selected a few of the more typical examples to serve as illustrations of the 
various phenomena observed. The maps accompanying the following de- 
scriptions were drawn by iV[r. Johnson from {)lane-table surveys made by 
himself, and are so truthful and graphic that they require but little interpre- 
tation. 

EMBANKMENTS AT THE WEST END OF HUMBOLDT LAKE. 

Humboldt Lake owes i^^s existence to the damming of the Humboldt 
River by extensive gravel embankments which were thrown completely 
across its channel during the time that Lake Lahontan occupied the valley. 
The topography about the west end of the lake is represented with accuracy 
on the accompanying map, Plate XVIH, which embraces the entire breadth 
of the former lake in this portion of the valley. The highest level of the 
ancient water surface is represented on the map by a heavy broken line, 
and appears in the topography of the country as a gravel embankment, or 
a wave-cut terrace at the base of a sea-cliff that is sometimes a hundred feet 



106 - GEOLOGICAL HISTOBT OF LAKE LAHONTAN. 

or more in height. On the western side of the valley this ancient water line 
is rendered especially noticeable by the cliffs of deep purple that mark its 
course. 

The narrow valley in which Humboldt Lake is situated was a strait at 
the time of the higher stages of Lake Lahontan, and connected the Carson 
body of the former lake with the waters that occupied the northern part of 
the Humboldt Valley. In its topographical relations it was similar to the 
constriction in the valley at the southern end of Winnemucca Lake, and is 
paralleled in the Bonneville basin by the narrow passage, now known as the 
Narrows of the Jordan, which connected the main body of Lake Bonneville 
with the Utah Lake body. In all these localities, and in many others 
similarly situated that have been studied by the writer in the basins of the 
extinct lakes of Utah and Nevada, the beach phenomena are greatly in- 
tensified, and bars and embankments of gravel are unusually well displayed. 

At the southern end of Humboldt Lake a single embankment of 
gravel from 50 to 125 feet in height" has been carried completely across 
the valley in such a manner as to suggest that it is an artificial structure 
intended to confine the drainage. At either end the main embankment 
widens as it approaches the shore and forms heavy tiiangular masses of 
gravel, on the sui-face of which appear many smaller bars built of clean, 
well-worn shingle. These secondary bars form ridges with rounded crests 
which vary from a few feet up to thirty or forty feet in height, and are 
nearly level-topped for long distances. These are seldom straight, but 
curve with beautiful symmetry, each gracefully bending ridge marking the 
course of a current in the waters of the ancient lake in which it was formed. 

The main embankment, i. e., the one crossing the valley, declines gently 
in height from either end towards the center, and has been cut through at 
its lowest point by the overflow of Humboldt Lake. The gap carved by 
the outflowing waters is shown in the profile at the bottom of Plate XVIII. 
The diagram was constructed from a line of levels run from the Lahontan 
beach on the Niter Buttes to the highest water line on the west side of the 
valley ; the points selected for the beginning and the end of the line were free 

;b given alwve 



/ 



EMBANKMENTS AT HUMBOLDT LAKE. 107 

bars with rounded crests, thus securing the highest records of wave action 
in this portion of the former lake. One result of these measurements is the 
proof that the beach lines on the sides of the valley, although formed at the 
highest water stage of the former lake, and therefore originally in the same 
horizontal plane, no longer have the same elevation. On the east side, the 
highest water line is now 498 feet above the level of Humboldt Lake, while 
on the west its elevation is 489 feet. Humboldt Lake, as shown by con- 
necting our line of levels with the profile of the Central Pacific Railroad, is 
3,929 feet above the sea. 

In studying those wave-built structures more minutely, we find that 
the one which crosses the valley is composed of worn and rounded pebbles 
of basalt, rhyolite, granite, and quartzite, together with fragments of black 
slate and occasional masses of cemented pebbles. The granite and quartzite 
and the volcanic rock forming some of the pebbles are only found in place 
in the vicinity on the north side of Humboldt Lake; consequently, the 
currents which carried them to their present positions must have come from 
the northeast and followed the western border of the valley until deflected 
by the topography of the coast. The direction of the currents that built 
this embankment is also indicated by its form; to the westward it presents 
a steep escarpment, but the eastern slope is quite gentle and, especially 
near its extremities, merges gradually with the alluvial slopes in the sides 
of the valley. The more gentle slope indicates the general direction from 
which the current-borne debris was derived. In the following section a 
profile of the bar is given, constructed with the same vertical and horizontal 
scale, from a line of levels run at right angles to the trend of the structure 
at a point about two miles west of the gap cut by the overflow of Humboldt 
Lake. 




LfiAi ^ 



7JO /•'ffi. 



Fro. 16.— Profile of ffravel crobankmcDt at went end of Hninboldt Lnlce. 

The topography of the embankment, therefore, as well as the material 
of which it is composed, indicates that it was built very largely by currents 
from the north. It is highest at the northern end, near where the railroad 



108 GEOLOGICAL HISTORY OF LAKE LAHONTAK 

crosses it, but maintains a nearly horizontal crest for at least a third of the 
way to the point where the river has cut through ; it then falls off with an 
abrupt descent to a level six or eight feet lower, the crest of the structure 
at the same time becoming broadened and curved slightly westward. Con- 
tinuing southward, one descends three more similar scarps of less height 
before reaching the lowest point in the embankment. Each of these 
descents is formed by the end of a comparatively thin layer of gravel that 
was added by the currents to the surface of the structure, and would no 
doubt have been can-ied along its whole extent had not a rise in the lake 
caused the cuiTents to begin the formation of another similar sheet of gravel 
near the shore and at a higher level. Each of the steps in the crest of the 
embankment represents a pause in the rise of the waters of the ancient lake. 
The highest in the series was the last formed. The incompleteness in this 
instance furnishes the suggestion that similar embankments which seem from 
their form to be homogeneous may in reality be highly compound. The 
irregular stratification of the embankment retaining Humboldt Lake is 
illustrated by the following sketch of the section exposed on the right side 
of the channel that has been eroded through it The general inclination of 
the strata on the west side of the embankment is much greater than on 







VkrticAl and HwlienUj SoaJ* 
Fio. 17.- Section of gravel embankment at went end of Hnmboldt Lake. 

the east, the reason being that in deposits of this nature the scarps sloping 
with the current are usually steeper than those inclined in the direction 
from which the current arrives. The lines of unconformability sloping 
gently westward in the upper part of the section indicate periods of erosion 
when the top of the structure was removed and subsequently rebuilt with 
current-bedded gravels. At the time these alterations were made, the lake 
surface in each instance must have been nearly on a level with the top of 
the embankment. 

The embankment crossing the valley is older than the branching 
structures forming the surface at either end, as is shown by the superposi- 
tion of the latter. This is well exhibited in the left side of the gap cut by 



EMBANKMENTS AT HUMBOLDT LAKE. 109 

the Humboldt, where the homogeneous black gravel composing the end 
bars rests directly on the more heterogeneous material forming the main 
embankment. Its greater age is also shown by its being inci-usted on its 
western slope by the three main varieties of Lahontan tufa hereafter to be 
described, while the end bars are almost entirely free from these deposits. 

In a terrace of black gravel on the northern slope of the Niter Buttes, 
dendritic tufa between heavy beds of gravel indicates that there were 
periods of bar building both before and after the formation of the tufa. On 
the north side of the valley, northeast of the north end of the main embank- 
ment, an arroyo has cut the gravel deposits so as to reveal an interbedded 
stratum of white marl; this again marks a division between two periods 
during which embankments were formed. These interruptions in the 
gravel deposits are noted now as a part of the facts observed in the region 
we are describing, but their connection with the history of the lake will be 
described in a future chapter. 

The embankments on the south side of the valley, as shown on Plate 
XVIII, appear, topogi'aphically, to be branches of the main structure, but 
in reality they were formed at a later date by curi'ents sweeping west- 
ward along the southern border of the valley. This is shown not only by 
their being tangent to the projection formed by the Niter Buttes, but is 
also evident from the nature of the material of which they are composed. 
The Niter Buttes and Mopung Hills are rhyolite, while the mountains skirt- 
ing the southern shore of Humboldt Lake are largely composed of black 
slate. The gravel forming the symmetric embankments at the base of the 
Niter Buttes is composed almost wholly of water-worn pebbles of black 
slate, and could only have been derived from cliffs of the same material to 
the eastward; the gravel of which the bars are composed may, in fact, be 
traced continuously to the quarries from which it was obtained. 

On the steep western slope of the Niter Buttes are a number of terraces, 
each of which records a pause in the fluctuation of the lake in which they 
were- formed. The most conspicuous of these is a broad shelf of black 
gravel which girdles the promontory at an elevation of 220 feet al)ove 
Humboldt Lake. The gravel forming this shelf consists of well-rounded 
fragments of black slate identical with those composing the bars at a lower 



110 GEOLOGICAL HISTORY OF LAKE LAHOSTAN. 

level, and derived from the same source. As the rock composing the buttes 
has a bright reddish tint, the position of this temvce is rendered conspicuous 
by contrast in color. At the southern side of the buttes this terrace leaves 
the steep slope and crosses an alluvial cone, changing at the same time 
from a terrace to a barrier bar with a rounded crest. In cross- section, like 
nearly all gravel bars, it exhibits an oblique stratification which is most 
pronounced on the lakeward slope. 




The angular alluvium on which the bar rests is largely composea of 
brightly-colored rhyolite, derived from the cUflfs above, while the bar, like 
the terrace of which it is a continuation, is almost wholly formed of pebbles 
of black slate, which indicate by their rounded forms and polished sur- 
faces that they have traveled a long way since leaving their parent ledges 
in the cliffs on the southern border of Humboldt Lake. On following 
these gravels still farther southward, we find that they again form a terrace, 
which soon loses its identity, however, on approaching the Mopung Hills. 

. The group of bars on the north side of the valley, like the correspond- 
ing structures at the base of the Niter Buttes, are level-topped ridges of 
clean, well-worn gravel, forming graceful curves; but the gravel in this 
instance was very largely contributed by currents from the west. The 
spaces inclosed by these ridges are in almost all cases floored witli light- 
colored mud, forming playas, which are converted into shallow lake- 
lets by every storm. The relative age of these bars may be determined in 
some instances by the superposition of one upon another, and by the fact 
that some are partially covered with tufa, while others, of later date, are 
free from that deposit. 

The complexity of these embankments, arising from the fact that they 
were formed at many horizons and at various stages in the former lake, 
together with the erosion and rebuilding that has taken place, renders their 



SUB- AERIAL AND SUB-LACUSTKAL TOPOGRAPHY. lU 

structure complex and their bearing on Lahontan history, L e.^ their value 
as records of Quaternary climate, exceedingly difficult to trace. From the 
occurrence of Lithoid tufa^ — the oldest variety found in the basin — on the 
western slope of the main bar, it is evident that the deposit of gravel at 
this locality was commenced early in the existence of the old lake, perhaps 
at the very first rise of its waters; and, as we have seen, enlargement and 
reconstruction have taken place at many subsequent periods and at many 
stages in the vertical range of the lake's surface. 

The trifling changes that have occurred in the area embraced by the 
accompanying maps, since the withdrawal of the waters of Lake Lahontan, 
are indicated by the arroyos or small water-courses cutting the embank- 
ments, and by the gap eroded by the overflowing waters of Humboldt 
Lake; with these exceptions, the structures are as fresh in appearance and 
as perfect in form as if they had been exposed to subaerial degradation for 
only a few years. 

The contrast in the topography above and below the Lahontan beach, 
in the region about Humboldt Lake, is so pronounced that it at once attracts 
the attention of the observer. The mountains above the level of the for- 
mer lake have the rugged and angular aspect characteristic of the subaerial 
erosion of arid climates, while below that horizon the topography is remark- 
able for its sweeping curves and flowing outlines. Hi the former instance 
the direction of the lines of erosion is controlled by the flow of rills and 
rivulets, and approaches the perpendicular; in the latter the predominating 
lines in the landscape are modeled by the waves and currents of a level 
water surface, and are therefore horizontal. The characteristics of the 
topography in one instance are due to subaerial, and in the other to sub- 
aqueous, conditions. 

Orographic movement has taken place on a grand scale in the region 
represented on Plate XVIII. This is illustrated by the great fault, with a 
throw of severial thousand feet, which determines the northwestern face of the 
west Humboldt Range. This fault passes between the Niter Buttes and the 
main range to the southward, and a curving branch determines the western 
face of the promontory formed by these buttes. The nearly perpendicular 

^ Thinolite and dendritic tufa also occar in abundance at thi8 locality. 



112 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

northern face of the Mopung Hills was also formed by the same displace- 
ment The greater part of the orographic disturbance in this region took 
phice previous to the rise of Lake Lahontan, and gave origin to the main 
features in the structure of the basin now occupied by Huml)oIdt Lake. 
Movements must have taken place along this Hne of fracture during the 
inter-Lahontan time, as is indicated by sloping terraces on the western face 
of the Niter Buttes. Since the withdrawal of the waters of the former lake 
the fault at the immediate base of the west Humboldt Range has increased 
its displacement 50 or 60 feet, and formed fresh scarps in Lahontan gravels 
(see Plate XLV). There has also been some recent movement in the branch- 
ing faults about the biise of the Niter Buttes, which may be traced for a 
considerable distance across the alluvial slopes to the westward, and appears 
again at the base of the Mopung Hills. The displacements, noticed above 
in explanation of the accompanying map, will receive further attention in 
Chapter X, which is devoted to post-Quaternary orography. 

EMBANKMENTS ON THE SOUTHERN BORDER OF THE CARSON DESERT. 

On the south shore of South Carson Lake there stands a bold, rugged 
promontory of basaltic rock that is girdled with terraces and incrusted with 
tufa about its base. During the existence of Lake Lahontan, this butte 
formed a high, rocky island, that was separated from the mainland to the 
southward by a narrow strait, partially obstructed by small islands, through 
which the currents must have swept with great force. On the southern or 
mainland border of the strait, the group of gravel bars represented on 
Plate XIX were formed. 

The changes wrought by waves and currents are marked with unu- 
sual distinctness all along the southern margin of the Carson Desert. 
This was the shore of the largest open water area of the former lake, 
and was exposed to the full force of storms from the north. The con- 
spicuous sea-cliff on the southern margin of the Carson Desert may be 
followed all the way to the pass near Allen's Springs, where it is bold 
and rugged, as represented by the heavy hachuring at the top of the 
accompanying plate. During the higher stages of the lake the currents 
«wept southward through the pass, carrying with them the debris of the sea- 



I 



'): 



l**^^'^^-«t*-y.''s^f^*'^5«PWr^ 




r DJ hiu T mq pk 



EMBANKMENTS NEAR THE CARSON DESERT. 113 

cliffs, and depositing it in less exposed situations under the lee of the prom- 
ontor)'- where the shore receded and formed a bay. The sickle-shaped bars 
with free extremities, which resulted from this action, indicate by their forms, 
as well as by the character of the pebbles and stones composing them, the 
direction followed by the currents to which they owe their origin. The hill 
represented at the top of the accompanying map is of white rhyolite, with a 
high, narrow spur of black anamesite projecting from its southern border. 
The latter rock also composes the hills represented in the southwestern por- 
tion of the map. Between these rugged outcrops there is a gentle slope of 
alluvium, cut by miniature drainage lines. The striking contrast in the color 
of the rock in place at either end of the embankments enables one to deter- 
mine at a glance the localities from which the stones composing them were 
derived. 

The broad, lightly shaded bands on the right of the map, having a 
southeast bearing, are low gravel bars that form the crest of the divide in 
the pass, or ancient strait, and are now separated by a smooth playa. The 
drainage north of these bars is into South Carson Lake, wliile the rill-lines 
south of them combine to form a water-course that leads eastward past 
Allen's Springs into the desert valley which opens southward. The curved 
bars, shown in the central portion of the map, are thus confined in vertical 
range between the highest water-line of the former lake, i, e,, the Lahontan 
beach, and the highest part of the pass in which they occur. This interval 
measures 114 feet, or, in other words, the water was 114 feet deep in the 
shallowest part of the strait at the time the highest embankment was formed. 

The highest of this series of gravel structures are shown at A and 
B on the map. A is a short, curved bar, 3 or 4 feet higher than the 
long, sickle-shaped embankment on which it rests, and is composed of well- 
worn stones and gravel of anamesite and rhyolite. That this bar was built 
subsequent to the much longer embankment beneath is proven by the 
stratification to be observed at its terminus. Its outer or lake ward 
slope is regular, with a curved contour that is the result of deposition. 
Had the lower embankment been built last, the outer slope of the higher 
structure would have been cut away by shore erosion, so as to form 

a sea-cliff. The embankment at B is at the same horizon as the smaller 
MoN. XI 8 



114 GE; LOGICAL HISTORY OF LAKE LAHONTAN. 

one at A. It leaves the shore and returns to it, thus forming a loop inclos- 
ing a cup-shaped depression 5 or 6 feet deep, now smoothly floored with 
playa mud. The long, curved bar C has a smooth, evenly rounded top and 
a nearly horizontal crest- line, which decreases slightly in height, how^ever, 
as we approach its southern end, where the curvature is more abrupt. Like 
all the embankments in the series, this is composed largely of rhyolite, with 
some anamesite, all rounded and well worn, but coarsest near its northern 
end. At its southern end it becomes broader, as well as more sharply 
curved, and shows three or four minor divisions, thus indicating that it is a 
compound structure throughout. The area to the westward of this embank- 
ment, once a lagoon, is now a playa, floored with smooth, horizontal, light- 
colored mud, that is unclothed with vegetation of any kind. That the 
embankment C is of a later date than the platform on which it rests is 
shown by the same kind of evidence that proves it to be of older date than 
the bars superimposed upon it. This is an interesting conclusion, as the 
bar below C is incrusted and cemented with lithoid tufa, thus showing that 
the higher bars were constructed after the formation of the calcareous 
deposit. The bar C is a portion of the water-line designated as the lithoid ter- 
race on page 101. The highest exposure of tufa is here about 25 feet below 
the Lahontan beach. A corresponding relation of the lithoid terrace to the 
highest beach line has been observed at a number of other localities in the 
Lahontan basin, and will again claim attention when the oscillations of the 
lake are considered. The outer margin of the platform on which the bar 
C rests has been cut away by waves and currents so as to expose a steep 
sea-cliff* of cemented gravel, and furnishes the only example in the group 
of a gravel structure that has suffered erosion by the wateis of the lake in 
which it was formed. Below this horizon are other curved and sickle-shaped 
embankments, the relative age of which is indicated by the manner in which 
they overplace each other. The topography of these structures, and the 
playas they contain, are faithfully represented on the accompanying map. 
The bars described above, with the exception mentioned, are unaffected 
by erosion, and are as smooth and regular as if their elegantly curved 
ridges were formed but yesterday. They afford beautiful examples of the 
symmetry of water-built structures. 



EMBANKMENTS AT BUFFALO SPRINGS. 115 

The sea-clifF marking the horizon of the highest water-hne is a conspic- 
uous feature on the more exposed shores in the area embraced by the 
accompanying map, but cannot be distinguished on the alluvial slopes of 
the bays, where the water was shallow and sheltered from waves and cur- 
rents. The material cut away to form the sea-cliffs shown in the lower 
part of Plate XIX was carried southward and built into a series of looped 
and V-shaped bars, inclosing deep cups, at another angle of the shore, a 
few hundred yards away. 

EMBANKMENTS AT BUFFALO SPRINGS, NEVADA. 

Passing north from Carson Desert, one crosses a low, narrow divide, 
once a strait in Lake Lahontan, and enters a valley having a broad playa 
in its central portion and surrounded on all sides by alluvial slopes, above 
which rise angular mountain crests. Around the borders of the valley, at 
an elevation of about 300 feet above the playa, the Lahontan beach can be 
traced with distinctness. The lowest point on the pass at the north end of 
the valley is higher than the Lahontan beach, and was never crossed by the 
waters of the old lake. The valley was therefore a typical cul-de-sac at the 
time it was flooded by Lake Lahontan. Owing to the abundance of loose 
material furnished by the alluvial slopes, the shore phenomena in the valley 
consist almost entirely of works of construction. The most common of the 
structures due to shore action are rounded beaches of gravel, looped bars, 
and peculiar embankments, not designated by a special name, that extend 
out nearly at right angles to the general trend of the ancient shore and form 
conspicuous features in the topography of the basin. A locality near Buf- 
falo Springs, at which these various features are well displayed, is repre- 
sented on Plate XX. On the map the crests of the bars are light and the 
slope of their sides represented by hachures. The figures at various 
points represent vertical distances in feet below the Lahontan beach, 
which is taken as zero. They may be considered as soundings made in the 
ancient lake during its highest stage. Each of the bars has the form of a 
railroad embankment, with a somewhat rounded crest ; they are even more 
clearly defined when examined in the field than they appear on the map, as 



116 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

the nature of their material and the general absence of vegetation from 
their surfaces serve to accent the topographic forms. 

Buffalo Springs are situated on the western border of the valley, at an 
elevation approximately 25 feet above the playa and 300 feet below 
the Lahontan beach. On Plate XX a portion of the border of the val- 
ley is represented which extends from Buffalo Springs to an elevation 
a short distance above the highest water line of the former lake. If the map 
had been continued a mile or two westward, it would have shown a greater 
portion of the sloping pediment of alluvium that surrounds the valley ; and it 
extended for an equal distance east, it would have embraced a portion of a 
much gentler slope which finally merges with the playa in the bottom of the 
basin. The alluvial slope represented on the map above the highest beach 
shows a few of the numerous drainage lines which during the infrequent 
rains conduct the surface waters to the bottom of the valley. The influence 
of the beaches in deflecting the water-courses is indicated, as is also the 
manner in which streams shift their channels, and sometimes bifurcate, on 
alluvial slopes. 

The first feature to attract attention on inspecting this group of embank- 
ments is the fact that they were built from the bottom up. The oldest in the 
series, so far as now exposed, is the lowest. The last formed is the Lahon- 
tan beach. Another division in reference to age is also possible, as a por- 
tion of the bars is coated with tufa, while other portions are free from 
that deposit. On referring to the plate it will be seen that the lowest well- 
defined beach occurs at a horizon 114 feet below the highest water line. 
This is a gravel ridge, forming an irregular V-bar, from the apex of which 
a somewhat curved embankment of gravel extends into the valley for about 
half a mile. The projecting bar is coated with lithoid and dendritic tufa, 
but the structures at a higher level are free from such deposits. The pro- 
jecting bar has also suffered from erosion much more than those at a higher 
level, and, besides, is coated with fine sediments. It thus appears that the 
structures below the level of the lowest well-defined beach were formed be- 
fore the deposition of the lithoid and dendritic tufas, while the bars and 
beaches above that horizon were built at a subsequent date. From data 
afforded at other localities we conclude that the construction of the higher 




A, 

.Ttii'liii „„ 

■'kiimv*,-'! ■■"■' ■ 



^%Hi|rri|ijr'l)i|,i|MJi!;j!l'liM!r"H-" 



IT. D. JolBjon, Tupograpker. 



I. 0. JhUHO, (hstiviM. 



GRAVEL FMOANKMENTS AT BUFI 



RINGS. fJEVAPA. 



EMBANKMENT« AT BUFFALO SPKINGS. 117 

lieacKes took place during the last high-water stage of the lake. This de- 
lermination, however, will appear more clear to the reader as we advance 
with our studies. 

An inspection of the map shows that all the structures there repre- 
jented were built in a rising lake, and were but little, if at all, modified by 
the waves and currents as the waters receded. This statement requires 
qualification however. We may be certain from the perfection of the ridges 
that the retiring waters did not tend to destroy them, but, on the other hand, 
they may have received additions. It is probable that gravel structures 
like those under discussion, when formed in a rising lake, would induce dep- 
osition at the same horizons during a recession of the waters. The sec- 
tions of the structures at Buffalo Springs fail to give information on this 
point. 

The only modifications that have taken place in these deposits in post- 
Lahontan times are due to the erosion of the rills that cross them and the 
partial removal of the fine sediment deposited over the older bars. 

At the extreme distal end of the embankment that projects into the 
valley there are considerable accumulations of sand, illustrating the fact 
that fine material is carried farthest by currents when structures of this char- 
acter are found, and showing why the bottoms of gravel embankments are fre- 
quently composed of sand. On either slope of the embankment the gravel of 
which it is composed is concealed beneath fine sediments, which must have 
been deposited when the lake stood over the structure. The looped bars 
high in the series at one time contained lagoons in which mollusks found a 
congenial habitat, as is shown by the multitudes of shells, principally of 
Pompholyx, that crowd the marls in the miniature playas behind a num- 
ber of the embankments. 

Three miles south of Buff'alo Springs there is another group of embank- 
ments similar to that described above. These are represented on the sketch- 
map forming Plate XXI.*® 

■"^This map is less accurate tbau the one forming Plato XX, but it indicates the main features of the 
structures as well as could be desired. The figures on Piute XXI are from aneroid measurements, and 
indicate approximately the depth of water at the highest water stage of Lake Lahontan. The figures 
on Plate XX are from measurements with an engineer's level, and may be considered accurate. 



118 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

All the structures in this group were formed mainly by currents from 
the south, which swept along the lake shore, carrying shore drift with them, 
and were deflected from the land upon arriving at the place where deposi- 
tion had been initiated. This is shown not only by the curvature of the 
terraces as they approach the bars, but also by the fact that the structures 
are much the steeper on the north side. 

In these beaches and embankments, as in those at Buffalo Springs, two 
clearly defined divisions may be seen, which are of different age. The 
long bar projecting into the valley and marked with the numbers 95 to 100 — 
indicating depth of water in feet at the highest stage of the former lake— is of 
older date than the group of v-shaped structures at a higher level. 

The main embankment has a broad, smooth top, which is covered in 
places with lithoid and dendritic tufa, and is partially coated, especially on 
the sides, with fine lacustral sediments. Below the point marked with the 
figures 190, there is a steep scarp nearly a hundred feet high, from the base 
of which the bar continues on in the same direction as at the higher levels, 
but is more deeply covered with sediments, and finally becomes so com- 
pletely inclosed that its presence is only indicated by the rise of the lacus- 
tral beds as they arch over the buried structure. The main embankment 
is thus older than the stages of the lake during which lithoid and dendritic 
tufa was precipitated, and was formed previous to a high- water period, during 
which the lacustral beds covering the structure were deposited. 

Considering next the group of v-shaped bars at the north of the main 
structure, we find that the base of this compound gi'oup, so far as is revealed 
by the topography, is older than the highest portion of the main embank- 
ment, which was built upon it The structures that occur from the Lahon- 
tan beach down to a horizon 75 feet below that level are of later date than 
the bar which is prolonged into the valley, as is shown by their freedom from 
both lacustral sediments and tufa deposits. 

The difference in age of the two main divisions of this group thus fur- 
nishes evidence similar to that presented at the Buffalo Springs locality. 
The higher structures in each case are the younger. These two groups are 
the complement of each other, however, in the fact that the one at Buffalo 
Springs was built principally by currents from the north, while the second 




T li J htuon Tfog aphtr I KufO, Ottlefit 

GHAVEL Et-PANKVENTSTHREfc MILES SOUTH UP BUFFALO RNO5. NEVADA 



EMBANKMENTS NEAR BUFFALO SPRINGS. 119 

group, three miles south along the same shore, was constructed almost 
entirely by currents from the south. 

The manner in which a gravel structure once started on the margin of 
a lake continues to induce deposition in case the waters rise, is well illus- 
trated by the group of bars at the right on Plate XXI, which is literally a 
pile of v-bars, the lowest in the series being the oldest. The thickness of 
gravel in this compound structure exceeds a hundred feet, and, as shown by 
the topography, the material composing it was nearly all brought from 
the south. 

Besides the embankments that have been specially examined, there are 
many others in the Lahontan basin of equal magnitude and perhaps equally 
instructive, which illustrate the variety of topographic forms produced by 
the action of waves and currents. 

On the east shore of Walker Lake are two localities where gravel em- 
bankments of large size have been built out from the old lake shore and 
form capes the ends of which are washed by the waves of the present lake. 
These may be distinguished on Phite XV by the manner in which the rail- 
road curves about them, close to the water's edge. At each of the localities 
there are a number of V-shaped gravel deposits that have been built one 
above another from a common base, so as to produce an exceedingly com- 
plicated structure. 

In Alkali Valley, about three miles west of Sand Spring Pass, is another 
locality where the gravel accumulated along the shores of the former lake 
may be studied to advantage. 

Other deposits of the same cliaracter may be seen on the east side of 
Humboldt Valley, between Rye Patch and Humboldt House, and again at 
the south end of Winnemucca Lake. A plat of the gravel structure at the 
last named locality is given below, which will serve as an illustration of the 
manner in which an embankment of large size may be thrown across a 
narrow strait so as to obstruct the drainage when the waters retire. 

The deposits at this locality are very similar to the embankment at the 
west end of Humboldt Lake, represented on Plate XVUI, and find a par- 
allel in the Bonneville basin in the immense bar at Stockton, Utah. In the 



120 



GEOLOGICAL HISTORY OF LAKE LAHONTAIf. 



instance before us, the gravel forming the embankment was brought by 
shore currents from the nortli, along the east side of Winnetnucca Valley, 
and deposited, when the current was deflected from the shore, so as to build 
the structure still remaining. This is a remarkably uniform embankment. 




Fio. IS.— Oninil embsukment at Mrath end of 'Wloiiemnow I-ak*. Nerad*. 

about 250 feet high, which has all the features of an artificial structure in- 
tended to dam the valley of Winnemucca Lake. Its western end does not 
reach quite to the west shore of the strait, and since recession of the waters 
in which it was formed it lias been truncated by the erosion of the branch 
of the Truckee River which flows into "VVinnemucca Lake. A portion of 
the section exposed by the removal of the end of the embankment is accu- 
rately shown in the following diagram 




EMBASKJIENT3 IS CUUKCHILL VALLEY. 



121 



On the west side of the gap through which the Carson River leaves 
Churchill Valley there is a group of curved bars that were built out from a 
small butte, once an island in Lalie Lahontan, Iiy currents flowing out of 
Churchill Valley. A note-book sketch of these structures is reproduced 
below, on a scale of about fjOO feet to 1 inch, which will serve to indicate the 
character of tlie phenomena found at this locality. 




mmsjM 



These bars or embankments are quite similar to those near Allen's 
Springs (see Plate XIX), and, as is so frequently the case, have been built 
from the bottom up; the highest in the series is the youngest. In examples 
of this nature, however, the deposit"!! made as the waters fell may have been 
added to the surfaces of the older structures. This is indicated in the ex- 
ample shown in the sketch, by the fact that the outer scarp of the higher 
teiTace a has been cut away, the material removed being spread out over 
the embankments c and d. In the illustration, a is about 20 feet below the 
Lahontan beach, while 6 is 20 feet lower. The surface of c is 25 feet lower 
than b, and on the same general level as d Both c and d decline gradually 
in elevation towards the distal extremity. The longest of the bars has been 
truncated by the erosion of the waters which sometimes flow down the 
arroyo shown in the sketch 

In the northern part of the Lahontan basin, fine examples of water- 
built gravel embankments maybe seen at the northern end of the Slumber- 



122 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



ing Hills, and at the corresponding extremity of the Jackson Range ; also, 
at the southern terminus of the Quinn River Mountains, and about Black 
Rock Point. All these localities were prominent headlands in the ancient 
lake, and were swept by strong currents which brought gravel and sand 
from the adjacent shore and deposited it on the salients of tlie land when 
the currents were forced into deep water. 

A note-book sketch of tlie embankment at the south end of the Quinn 
River Mountains is reproduced in the following diagram : 




Flo. 22.— Sketch of gravel clubuilimtnis nt BouUi .nd of Quinn River UounUins, Herado. 

The embankment is about 1,500 feet long, and at the point where the 
profile was sketched is 100 feet broad and 40 feet high. It projects from a 
salient where the current from Quinn River Valley left the shore on enter- 
ing the strait between tlie Quinn River Mountains and the Slumbering Hills. 
The valley at this point is about 4 miles broad, and, during the existence of 
the ancient lake, formed a strait connecting two comparatively large water- 



DELTAS OF THE AXOIENT LAKE. 123 

bodies. The embankment was built by currents from both the north and 
the west, and was carried out over horizontal lacustral beds, as represented 
in the sketch. 

The buttes in King's River Valley were islands in Lake Lahontan and 
became surrounded by terraces, bars, and embankments that were built by 
the currents sweeping past them. 

The topographic forms produced by the deposition of gravel in the 
paths of currents are extremely varied, and usually present curving con- 
tours and smooth, rounded crests, that are in marked contrast to the angular 
mountain slopes rising above them. Wherever the current-built structures 
of ancient lakes occur, one is sure to find an illustration of the striking 
contrast exhibited by the angular reliefs produced by subaerial erosion, and 
the rounded and flowing outlines resulting from the action of waves and 
currents. Aside from the bearing that these gravel embankments have on 
the geological history of the basin, one may always derive aid from them 
in determining the action of currents in existing lakes. The hydraulic engi- 
neer will do well to study the processes employed by nature to accomplish 
results that are frequently analogous to the works desired by man for im- 
proving navigation or providing a haven for shipping. 

DELTAS. 

The study of the records left by Lake Lahontan has added but little 
to our knowledge of deltas, for the reason that the lake was too inconstant 
in level to favor their formation, and also because nearly all the tributary 
streams entered the lake at the heads of naiTOw bays and estuaries, which 
were unfavorable localities for the development of structures of this nature. 
The Humboldt River entered the Lahontan basin at the head of a long, 
narrow arm of the old lake, which became deeply filled with debris, but is 
not now exposed in section. Farther southward in the same valley, between 
Mill City and Oreana, the Lahontan strata are well exposed, and will receive 
attention under the section devoted to sedimentary deposits. In the south- 
ern portion of the section to be seen in the banks of the Humboldt River 
there are incHned strata that have a striking resemblance to delta structure, 
but after a careful examination it was concluded that they owe their inch- 



124 GEOLOGICAL BISTORY OF LAKE LAEOXTAN. 

nation to their having been deposited by currents on the steep slopes 
of gravel embankments. That much of the material now filling the Hum- 
boldt Valley was brought down by the river, and is in reality of the nature 
of a delta deposit, there can be little doubt, but it lias mostly been re- 
an-anged by currents and the topographic form of a delta is wanting. The 
same is true also of the accumulations at the points where the Truckee and 
Carson rivers entered the lake; about the ancient mouths of these streams 
there is a thickening of the river-borne debris, but no distinct delta forms 
are visible. The canons of Buffalo and Smoke creeks were excavated to 
their present depth before the existence of the lake, and during the time the 
basin was flooded each of these channels formed a long narrow inlet which 
became deeply filled with sediments. When the lake's surface was lowered, 
the greater part of this material was removed by stream erosion ; and so far 
as the history of their deltas is concerned, there is no more to be said than 
in the case of the larger rivers. 

Nowhere in the Lahontan basin are deltas to be found that are com- 
parable with those formed along the bold eastern shore of Lake Bonne- 
ville, or those deposited in the Mono Lake basin by streams that descended 
the eastern slope of the Sierra Nevada. 



Section 3.— SEDIMENTS OF LAKE LAHONTAN. 

The tributaries of lakes — disregarding organic substances — contain two 
classes of impurities, (a) mineral matter in suspension, and (b) mineral 
matter in solution. 

Besides holding fine silt in suspension, streams also roll pebbles and 
stones along their beds. On entering a lake all this material subsides more 
or less quickly, forming lake-beds, gravel-deposits, etr. In the sedimenta- 
tion of lakes the coarser and heavier debris is invariably dropped near 
shore, w^hile the finer and lighter substances are floated to a greater distance 
before subsiding. In this manner coarse shore and fine off-shore deposits 
originate. The shore deposits of Lake Lahontan have already received 



:*»l 



.'•.-' ! 



1:. 



. . I 



> . 1 



i ' I ■ t ■ 



;i . 



t , ] 



CLASSIFICATION OF DEPOSITS. 125 

some attention. In the present division the off-shore sediments, or lake-beds 
proper, together with certain interstratified gravels, will be described. The 
mineral substances contributed to the lake in solution will be studied in 
connection with its chemical history. 

The sedimentary deposits of Lake Lahontan exhibit three definite divis- 
ions, viz.: 

Upper lacustral clays. 

Medial gravels. 

Lower lacustral clays. 

Wherever any considerable section of Lahontan sediments is exposed 
these three divisions appear in unvarying sequence. 

The upper and lower members of the series are composed of marly 
clays, which show by their fineness and the evenness of their lamination 
that they were deposited in deep still water. The middle member, on the 
other hand, usually consists of well-rounded gravel and san.d, in some in- 
stances becoming coarse and including bowlders a foot or more in diameter. 
This deposit is current-bedded, and exhibits many variations, indicating that 
it was deposited in shallow water. 

It is apparent, therefore, tliat the evenly stratified beds at the base and 
summit of the series are tlie records of a deep lake of broad extent, and 
mark periods of comparatively abundant precipitation or of greatly de- 
creased evaporation. It is also evident tliat tlie medial gravels were 
deposited when the lake was sufficiently lowered to allow stream and cur- 
rent-borne debris to be carried far out over the })reviously formed lake- 
beds, recording an interval of low water in the history of the lake. The 
significance of these dei)osits in reference to Quaternary climatic changes 
will appear more clearly in the sequel. 

Sections of Lahontan sediments are well exposed in those portions of 
the canons of the Humboldt, Truckee, Carson, and Walker rivers that are 
below tlie highest water-line of the former lake; and as the sections observed 
present facts of interest in tracing the Quaternary history of the region, 
together with many illustrations of geological structure, we shall give some- 
what detailed descriptions of the principal exposures. 



126 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

The illustrations of sections accompanying the following pages were 
drawn by Mr. W J McGee, to whom I am also indebted for a number of 
the observations here included. 

EXPOSURES IN THE CASTON OF THE HUMBOI^DT. 

Between Golconda and Humboldt Lake the Humboldt River flows in 
a channel that it has excavated in Lahontan sediments since the last desicca- 
tion of the ancient lake. For a number of miles below Golconda the river 
is practically a surface stream, with low banks of marly clay belonging to- 
the upper lacustral series. x\t Mill City its channel commences to deepen, 
and at Rye Patch the river flows a little more than two hundred feet below 
the general level of the desert. The general appearance of the gorge exca- 
vated by the river through the plain formed of lacustral sediments is showit 
in the accompanying illustration, Plate XXII, which is a reproduction of a 
photograph taken on the brink of the cailon, opposite Rye Patch. Through- 
out this portion of the cafion the tripartite division of the strata exposed in 
the steep banks is easily distinguished where not obscured by debris slopes. 
Below Rye Patch the banks decrease in altitude, and south of Oreana they 
are seldom more than 40 or 50 feet high, and only exhibit sections of the 
upper lacustral clays, with traces here and there of the medial gravels. 

A section of the beds exposed in the sides of the Humboldt Cafion be- 
tween Mill City and Lovelock Station, a distance of over 50 miles, is rep- 
resented at the top of Plate XXIII. This section was compiled from about 
25 detailed sections, which were first drawn at their proper place on the 
general diagram and then united in the manner that a somewhat extended 
study of the exposures seemed to dictate."*^ A few local sections, drawn with 
the same vertical and horizontal scale, are represented in the lower portion 
of the plate, and illustrate the diversity that prevails throughout the expos- 
ures. The most striking feature in the general section is the thickening 
of the deposits near Rye Patch, where they form an arch that once com- 
pletely dammed the valley and was subsequently dissected by the river. 
The hypothesis framed by the writer in explanation of the phenomena ob- 

*'' This illustration is perhaps open to the criticism that too much prominence has been given to^ 
the apparent plication of the strata. 






wjutot no. 



SECTlOMS OF LAHONTAr 




/. V. K^ofO, Qnlcgiil. 



HUMBOLDT CaRON, NtUAUA. 



DEPOSITION OF INCLINED BEDS. 127 

served is that the beds were deposited by cuiTents in the position the)'' still 
retain during the time that the Humboldt Valley was occupied by the 
waters of Lake Lahontan. In other ^vords, the inclined strata seen in the 
cafion walls are sections of current-formed embankments that have been 
buried beneath the upper lacustral marls. They are arches of deposition, 
and not plications due to orographic disturbance. 

The formation of gravel embankments across narrow straits in such a 
manner as to completely close them has already been referred to in describ- 
ing a structure of this nature at the lower end of Humboldt Lake (awfe, 
page 108). The study of current-formed gravel deposits in a large number 
of the desiccated lake-basins of the Far West strongly favors the conclusion 
that the inclination of the strata exposed in the walls of the Humboldt 
Cailon is due entirely to their mode of accumulation. Could the gravel 
embankments familiar to us in many narrow valleys become buried beneath 
lake sediments and then exposed in cross section by erosion, they would 
furnish examples of strata increasing in thickness at the same time that they 
became inclined and arched, which would in many ways be the counterpart 
of the phenomena illustrated by the section on Plate XXHI. 

The hypothesis that the dip in the sections w^e are considering was due 
to plication, in the manner common to many older rocks, suggested itself 
early in the investigation, but did not find supj)ort in the facts observed. 

The contacts of the lower and upper clays with the medial or gravel 
member of the series are nearly always unconformable. In many instan- 
ces the siu'face of the lower marls was eroded into hollows and channels 
previous to the deposition of the gravels, and these are now filled with 
current-bedded drbris in the manner illustrated bv section K, Plate XXHL 
Similar imconforuiities by erosion are also to be observed at many points 
where the contact of the medial gravels with the upi)er marls is exposed, 
as shown at I, on the same plate. Other illustrations of unconformity in 
the contact of the medial gravels with the evenly stratified beds above and 
below them are shown in the remaining detailed sections of Plate XXIII. 

A comjiarison of the upper and lower clays indicates that they are 
very similar in their nature and were probably accumulated under nearly 



128 



GEOLOGICAL niSTORY OF LAKE LAHOi^'TAK 



identical conditions; they are both evenly laminated, fine-grained, drab- 
colored clays, that are usually marly and saline, and frequently exhibit a 
well-marked jointed structure. An analysis of a typical example of each, 
as reported by Dr. T. M. Cliatard, shows that they do not differ more widely 
in composition than might be expected in two samples taken at different 
points in the same stratum. 



Constilnents. 

Loss by i^ition (water) 

Silicii(SiO») 

Alumina and ferrous oxide (AlsOs, and FesOs) 

Lime (CaO) 

Magnesia (MgO) 

Potassa (KsG) 

Soda(Nn«0) 

Total 



Upper clays. 


Lower clays. 


9.78 


13.03 


56.30 


50.70 


21.60 


19.01 


5.45 


10.20 


2.64 


3.19 


2.17 


2.16 


2.60 


1.91 


100.54 


100.26 



The upper clays differ from the lower, however, in the fact that at 
some localities they include interstratified beds of homogeneous, white, 
pumiceous dust, forming even layers from a fraction of an inch to several 
feet in thickness; and also a deposit of tufa in peculiar mushroom-shaped 
forms. The layer of fine marly clays on which the tufa stratum rests fre- 
quently teems with Cypris cases, and sometimes contains the shells of 
Fompholyx effusaiw immense numbers; above the tufa the shells o{ Anodonta 
nuttaUiana are frequently abundant. In the lower clays the relics of mol- 
luscan life are comparatively rare; and, so far as has been observed^ they 
contain no deposits of volcanic dust; this, however, may be considered as 
an accidental circumstance dependent on the periods of eruption of distant 
volcanoes. The layer of tufa in the upper clays is a widely spread deposit 
indicatinor chemical conditions that so fiir as is known — the entire thick- 
ness of the lower clays not being exposed — did not occur previous to the 
formation of the medial gravels; although lenticular masses and thin sheets 
of tufa of a somewhat similar nature are not uncommon in the lower por- 
tion of the Lahontan section. 

The medial gravels are in many places plainly divisible into two 
portions; the lower, composed of clean, well-worn, current-bedded sand 
and gravel, has all the structural characteristics of stream-bed and shore 



SECTIONS EXPOSED IN HUMBOLDT CASTON. 129 

formations; the upper is of a homogeneous, earthy character and has a 
striking resemblance to recent flood-plain deposits. The remarkable sim- 
ilarity of the middle member of the Lahontan section, as exposed in certain 
localities, to the bipartite — stream-bed and flood-plain — deposit formed by 
meandering streams, leads us to refer its origin with considerable confi- 
dence to similar causes. In some instances the earthy or flood-plain 
portion of the medial gravels is overlaid by current-bedded debris^ which 
may reasonably be considered as the sheet of shore material spread out by 
the waves and cuiTents during the rise of the lake that followed the forma- 
tion of the middle member of the series. 

The accuracy with which the accompanying detailed sections have 
been drawn, leaves little room for description; but in order to present 
still more definitely the facts on which they were based, descriptions of a 
few of the more instructive exposures are inserted. The lettering of the 
following sections indicates their position on Plate XXIII:*® 

Section A. — West hank of Humboldt River ^ 2 milea south of Oreana. 

Feet. 

1 . ^olian sand and dust, forming surface of the desert . 1 

2. Sand and gravel, massive 3 \ 

3. Loam, sand}^ laminated 2 >,Upi)e lacustral clays 

4. Marly clay, laminated and jointed 18 ) 

5. Sand and gravel, cross-stratitied 1 \ 

6. Loam and sand, obscurely cross-stratified 5 >Meilial gravels. 

7. Sandy loam, massive ; to river 3 / 

33 

A double fault-line extends through the series, as shown on Plate XXIII. 
A similar double fault occurs 300 feet northward of the first, in the same 
vertical cliff (see Fig. 26, page 165), but the throw is in the opposite direc- 
tion, showing that the whole inchided block, 300 feet long, has been bodily 
depressed 2 or 3 feet. The marly clays forming the upper portion of 
the section are, as usual, markedly unconformable to the gravels underlying 
them. 

^'In making the drawings of detailed sections represented on Plate XXIII, the entire vertical 
range of the exposures observed was not represented. 

MoN. XI 9 



VM) 



GEOLOGICAL HI8TOBY OF LAKE LAHONTAN. 



Sbction B,— We9t hank of Humboldt BiveTf i wiUe above Oreana. 

1. Marly clay, light colored, sandy 90 

2. Marly clay, yellowUh, fine-grained, laminated 

3. Marly clay, light colored, sandy, like No. 1 

4. Gravel, crom-bed, ferruginous 

5. Marly clay, drab-colored 

6. Gravel, oross-bedded, ferruginous 

7. Marly clay, finely laminated. Jointed 5 

8. Marly clay, more sandy than No. 7, tjbick-bedded ; to river 15 

61 

The exposures in this portion of the caiion walls vary greatly as one 
follows them up or down stream. The middle member especially changes 
in both the character of the strata and their inclination. 



Section C. — IFe^i bank of Humboldt River ^ 2^ miles above Oreana, 

Feet. 

1. Sand and gravel 12 

2. Marly clays, white, laminated 12^,^ , , , 

3. Marly clayB, brownish, loams 10 I "PP*" lacuetral days. 

4. Marly clays, white 25 J 

5. Gravel and sand, cross-stratified 25 Medial graveld. 

6. Marly clays and loam ; to river 10 Lower lacnstral clays 

94 
Section F.—West bank of Humboldt Biver, at Bye Patok, 



1. ^olian sand and alluvial gravel, variable 

2. Loaui, sandy, light-colored, fine 

3. " Tufa mushrooms" (dendritic tufa) 

4. Ostrocoid and gasteropod shells 

5. Sand, loamy, bufi'-colored, with small concre- 

tions of gypsum 

6. Gravel, rounded, cross-stratified 

7. Marl, bufi'-colored 

8. Gravel, cross- stratified 

9. Loam, with some cross- bedded gravel 

10. Gravel, cross-stratifie<l 

11. Sand, cemented by carbonate of lime 

12. Loam, fine, cross- stratified 

13. Sand, white, marly (much thicker in east 

wall of cafion"^ 

14. Loam, with irregular strata of gravel 

15. Gravel, cemented 

1(). Loam and fine gravel ; to river 




Upper lacnstral olays. 



^Medial gravelB, 



4 

40 

1 

75 



Lower lacnstral clays. 



196 to 201 



The separation of the three members is more difficult to trace in this 
locality than is usual; the above divisions are somewhat arbitrary. 



>■ Upper lacustral olays. 



SECTIONS EXPOSED IN HUMBOLDT OASTON. 131 

Section H. — North bank of Humboldt Riverj 6 miles below Mill City, 

Feet 

1. ^olian sands, wifchsome gravel, irregnlar in thick- 

ness 

2. Marly clay, ^yfaite, regularly laminated, jointed 15 Upper lacnstral clays. 

3. Loam, sand, and gravel, massive medially, cross- ^\f d' 1 1 

stratified above and below 12 ) ^ 

4. Marls, regularly laminated, light drab ; to river.. . 10 Lower laonstral days. 

37 

The medial gravels are markedly unconformable by erosion to both 
the upper and lower lacustral beds. 

Section Jj,— -South bank of Humboldt Rivera Mill City. 

Feet 

1. Weathered marl, SBolian sand at summit 2. 5 

2. Marly clays, obscurely stratified, gray 3. ' 

3. Marly clays, white, laminated 3. 

4. Marly clays, sandy, brownish, obscurely cross- 

stratified 'i. 5 

6. Marly clay, white, laminated, jointed 9.0. 

6. Sand and gravel, somewhat ferruginous, fossilif- >^ 

erons 0. 5 

7. Sand, gravel, and pebbles, cross-stratified 5. 

8. Sand and loam, massive, with pebbles 5. 

9. Sand and loam, obscurely and irregularly stratified . 4. 

10. Sand and gravel, with ferruginous current 0. 3 

11. Sand, cross-stratified, fine 3. 0-^ 

12. Marly clays, regularly laminated, ash colored, J Lower lacustral clays. 

jointed, with some tufa at summit ; to river 3. 5 

40.8 

The tufa in the lower lake-beds occurs in uniform lenticular nodules, 
in places forming a continuous layer an inch or two thick. Dendritic tufa, 
in the form of mushrooms, occurs in the upper lake-beds above No. 5, near 
where this section was taken. 

EXPOSURES IN THE CAS^ON OF THE TRUCKEB. 

The sedimentary deposits accumulated in Lake Lahontan are also well 
exposed in its precipitous banks of the Truckee River from the point where 
it enters the basin of the former lake, about 15 miles westward of Wads- 
worth, to its termini in Pyramid and Winnemucca lakes. Above Wads- 
worth the exposures are entirely of upper lacustral clays, which occur in 
fragmentary masses on the sides of the canon in places where they have 



>■ Medial gravels. 



132 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

been sheltered from erosion. The western bank of the Truckee just below 
Wadsworth, and 2 or 3 miles from the gorge through which the river enters 
the valley, is about a hundred feet high and exposes the following diversi- 
fied sections: 

Feet 

1. ^oliau sauds 5tol8 

2. Saudy clay, tiue, oveuly stratiGod 12 

3. Clay, drab-colored, fiue-graiiicd, lioiiiogcneous tt 

4. Clay, evenly stratitied, ferrnginous 1. 5 

5. Saud, argillaceous, iu contorted strata 3 

t). Sand, fine, clean, sharp 2. 5 

7. Clay, sandy, ferruginous, jointed 2 

8. Sand, coarse and pebbly 5 

9. Clay, argiUaceous 2 

10. Sand, ferruginous 10 

11. Clay, drab-colored, with seams of tine sand 2 

12. Sand and gravel, micaceous 10 

13. Gravel, well rounded, with seams of sand and occasional boulders 

sometimes 2 feet in diameter 6 

14. Sand, evenly stratified, micaceous, ripple-marked 2 

15. Sand, sharp, clean, micaceous 12 

16. Sand, evenly stratified, micaceous, ripple-marked and current- 

bedded ; passing into — 3 

17. Clay, fine, evenly stratified, drab-colored, sometimes saudy; jointed 

by two systems of fractures nearly at right angles, and resting un- 
conformably upon — 6 

18. Gravel, well rounded, current-bedded, and containing boulders 2 feet 

in diameter; to river 20 

110 to 12.^ 

The numerous changes recorded by this section are no doubt to be 
accounted for by the proximity of the former mouth of the river, from which 
the greater part of the ddbris forming the beds was derived. 

A noticeable feature of the section is the fine exhibition of double 
jointing to be seen in bed No. 17. This stratum is of compact and nearly 
homogeneous, sandy clay, resting on a thick deposit of unconsolidated 
gravel and bowlders, and overlain by similar material. As the inclosing 
beds are too loose and incoherent to exhibit jointed structure it seems 
evident that the forces producing the joints must have originated in the 
clays themselves; for it is difficult to understand how external agencies, ^s 
an earthquake shock for example, could have been transmitted through the 
loose gravel deposits inclosing the clays. The jointed stratum to which 
we have called attention apparently represents the lower lacustral clays, but 
as the section is rendered abnormal by its proximity to the ancient mouth 









WJ iltOm. IM. 



SECTIONS CF LAHONTAI 



^ 







1. V. XuorU. Hr-tuyiiL 



TRUCKEE CANON, NE( 



SECTIONS EXPOSED IN TEDCKEE CASTON. ' 133 

of the Truckee River, the three divisions of Lahontan sediments so easily 
recognized in many locaHties are here indefinite. 

Continuing towards Pyramid Lake with our study of the exposures in 
the river banks, we find the section changing in its details and losing the 
complex character observed at Wadsworth. Beginning a mile or two below 
the position of the section given in detail above, and continuing for four or 
five miles down the river, the exposures are almost entirely of upper lacus- 
tral clays, including a few irregular strata of current-borne material. This 
is indicated by the following section observed on the west side of the river 
about four miles below Wadsworth: 

Feet. 

1. ^olian sand 1 to 2 

2. Dendritic tufa in uiushroom-fonii.s 1 to 1. C) 

3. Clay, fine, sandy, ferruginous 4 

4. Clay, compact, drab-colore<l V2 

5. Sand, fine, ripple-marked 1 

0. Clay, fine, evenly stratified 2 

7. Sand and gravel, current-bedded I 

8. Clay, drab-colored 8 

1). Saud, ripple-niarked 1 

10. Clay, evenly stratified, with some sandy layers; tr> river 10i> 

Near the locality where this section was observed, but on the opposite 
side of the stream, the lower fifty feet of the cafion wall are composed of 
coarse gravel which evidently represents the middle member of the Lahon- 
tan series; half a mile down stream, however, the entire section is again 
composed of lacustral clays. 

Other abrupt changes of this nature are common and seem to indicate 
that the medial gravels occupy an old eroded channel in the lower clays, 
which is crossed irregularly by the present stream channel. 

Continuing down stream, one finds good exposures of the upper clays 
resting on coarse current-bedded gravels which are without question a por- 
tion of the middle member of the series. The medial gravels are here 
probably represented in part by A heavy deposit of reddish-brown debris, 
somewhat coarser than the normal lacustral clays and having a close resem- 
blance to the upper or flood-plain portion of the medial griavels observed 
in the Humboldt section. On the east side of the river this deposit becomes 
thinner as we follow it westward, and at length disappears in a thin wedge, 



134 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

at the same time increasing in thickness in the west bank of the cafion, 
until it finally composes the entire section of more than a hundred feet 

Just before the Truckee Canon opens out into the valley occupied by 
Pyramid and Winnemucca lakes, it becomes quite narrow, and is bounded 
on either side by rocky walls; for convenience of reference we have called 
this the ** Truckee Narrows." From this point to the Agency Bridge, a 
distance of about four and a half miles, the walls of the cafion exhibit a 
continuous section in which the tripartite character of the Lahontan sedi- 
ments is strikingly displayed. The exposures actually observed on the east 
side of the stream have been sketched by Mr. McGee and form Plate XXIV. 
The most instructive feature illustrated by this section, as is the case of the 
exposures along the Humboldt, is the fact that it consists of two series of 
fine homogeneous strata, separated by a heavy deposit of heterogeneous, 
current-bedded gravels. A generalized section of the beds here exposed 
agrees in a remarkable way with the similar sections observed in the Hum- 
boldt Cafion. The upper and lower lacustral clays occumng ip the Truckee 
section, like those exposed in the banks of the Humboldt, show but little 
variation. They are composed of fine, evenly laminated, drab-colored, 
marly clays, that are somewhat saline and alkaline as indicated by chemical 
tests. On the west side of the river near the Agency Bridge, however, the 
upper clays show some variation, especially near their contact with the 
underlying gravels, as is exhibited with considerable detail in the section 
forming Plate XXV. 

One of the most instructive portions of the Truckee section is a stratum 
of dendritic tufa interbedded with the upper clays. At the northern end of 
the section, i. e., towards the deeper portion of the lake in which the sedi- 
ments of tufa were deposited, the tufa-stratum is but 3 inches thick and is 
buried beneath 25 or 30 feet of laminated clay; when followed shoreward, 
or up stream in reference to the present drainage, the tufa gradually increases 
in thickness, at the same time approaching nearer the surface of the section, 
until at the Narrows of the Truckee it forms a sheet of huge mushroom-shaped 
masses at the top of the bank, which are from 10 to 15 feet in diameter and 
so thickly planted that they form a continuous pavement fully 10 feet thick. 
The rocks at the Nan-ows above the level of the lacustrine deposits are 



SECTIONS EXPOSED IN TEUCKBE OASfON. 135 

coated with a continuation of the same tufa sheet, the upper limit of which 
is about 200 feet below the highest of the ancient water-lines engraved 
on the sides of the valley. The tufa interstratified with the upper clays 
almost invariably starts from small nuclei, and, forming dendritic branches, 
spreads out above into dome or mushroom-shaped growths ; in some instan- 
ces the tufa is prolonged downward below the general level of the stratum 
to which it belongs, and forms iiregular vase-shaped masses below the con- 
tinuous tufa layer. Immediately below the tufa, and sometimes adhering 
to it, are great quantities of Cypris and gasteropod shells, and occasionally 
bones of fishes, indicating that the waters from which the calcium carbonate 
forming the tufa was precipitated were far from being concentrated saline 
solutions. 

Throughout the section, the contact of the medial gravels with both the 
underlying and the overlying clays is unconformable, owing, in each case, to 
the erosion of the lower member, as is well shown in Figs. A, C, and D, 
Plate XXVI, which are accurate sketches of observed exposures, and illus- 
trate the filling of channels, formed principally by erosion, with current- 
bedded gravel. 

The lacustral clays forming the lower portion of the section are, in 
places, exposed to the depth of 100 feet, but what their total thickness may 
be it is not possible to determine from the present exposures. When exam- 
ined at some distance from the shore of the basin, they exhibit little varia- 
tion, and are normally finely laminated, marly clays An exception is found, 
however, a short distance above the Agency Bridge, on the east side of the 
river, where a rounded boulder of hard volcanic rock from 2^ to 3 feet in 
diameter occurs several feet below the top of the lower clays. This is a 
much larger block than any seen in the medial gravels, and evidently must 
have been floated to its present position, probably through the agency of 
ice. Although rounded and worn it did not exhibit striations or planed sur- 
faces, and gave no proof that it had ever been subject to glacial action. 

In places, the lower clays exhibit contortions which in some instances 
can only be accounted for by a movement of the beds since their deposition, 
caused apparently to the weight of the superimposed masses of gravel and 
clay. In other exposures the contortions and convolutions of the laminated 



136 GEOLOGICAL HISTORY OF LAKK LAHOKTAN. 

deposits are apparently due to their liaving been formed in agitated waters ; 
just how the intricate folds and contortions were produced, however, it is 
extremely difficult to explain. 

In a few localities the lacustral clays, especially below the medial 
gravels, are faulted ; and at times the strata on one side of a fault have 
been thrust over the beds forming the opposite wall, as indicated at the left 
on Plate XXV. In this instance the projecting strata seem to have been 
removed by erosion previous to the deposition of the superimposed clays. 

The medial gravels in the Truckee section vary from 2f) to 100 feet in 
thickness, and exhibit great diversity both in composition and structure, 
thus indicating many variations in their mode of formation. Examples of 
cross-bedding are abundant, and the presence of arched strata and lines of 
unconformability, as well as the irregularity of the beds and the manner in 
which they wedge-out and are replaced by others of a somewhat different 
nature, all tend to show that the entire middle member of the Lahontan 
series here exposed was deposited in shallow, current-swept waters. The 
arches seen in the cation walls are, apparently, cross-sections of current- 
built embankments, while the irregular layers of fine sediment are proof, on 
the other hand, of more quiet condition during which the fine silt held in 
suspension was allowed to subside. The general conclusion that the medial 
gravels were formed during a time of low water, separating two periods when 
the lake was broad and deep, cannot be questioned by any one who has 
examined the records exposed in the Truckee section, which, as previously 
stated, are in harmony with the similar evidence furnished elsewhere in the 
basin of the ancient lake. 

On following the Truckee River from the Agency Bridge to its mouth, 
one finds its banks becoming low, and exposing, for the most part, only por- 
tions of the upper clays ; in a few localities, however, limited sections of 
the medial gravels may be seen, thus showing that the valley could not have 
held a lake much, if any, larger than that of the present day during the time 
that the medial member of the Lahontan series was being deposited. 



1— Lall-Jmb rtw. li.-k \i (Vprl. .h-ll* 



ON OF LAHONTAN StDIMENTS, AGENCY CniDGE, TRUCKEE RIVER, NEVADA. 



CHURCHILL VALLEY. 137 

EXPOSURES IN THE CAK^OX OF THE CARSON BIVEB. 

During the highest stages of Lake Lahontan its waters extended up 
the Carson River Valley as far as Dayton, and occupied it long enough to 
allow large quantities of lacustral beds to accumulate. When the lake 
evaporated and the river regained its ancient channel, these beds were deeply 
dissected by erosion. The remnants of Lahontan sediments to be seen in 
the valley belong mostly to the upper lacustral clays, but in places they 
were observed to rest on gravel deposits. The sections obtained, however, 
were imperfect and far less satisfactory and instructive than those described 
in the preceding pages. The lacustral beds exposed along the banks of the 
Carson, and flooring Churchill Valley, are fine, light-colored marly-clays, 
similar in all respects to the corresponding beds observed at many localities 
throughout the Lahontan basin. Interstratified with these sediments is a 
deposit of dendritic tufa, sometimes 3 or 4 feet in thickness, which is well 
exposed in the narrow channel connecting Churchill Valley with the Car- 
son Desert. This deposit corresponds both in structure and position to the 
interstratified tufa-layer observed in the Humboldt and Truckee cations. 

So far as known, the lacustral beds observed along the Carson River 
are undisturbed by post-Lahontan movement, and have nowhere been dis- 
sected sufficiently deep to lay open the sediments accumulated during the 
first rise of the lake. 

The Carson River rises on the eastern slope of the Sierra Nevada and 
flows northward through Carson and Eagle valleys, which are in reality a 
single basin, and enters a deep and all but impassable cailon, through which 
it flows with a rapid descent as for as Dayton. It then enters a valley 2 or 
3 miles broad — once an arm of Lake Lahontan — which contracts again to 
a narrow cafion at its southern end. In the course of a few miles this cafion 
again expands and fonns Churchill Valley, which in its turn connects with 
the Carson Desert through a narrow channel now occupied by the Carson 
River. The contractions in the lower portion of the river channel are prob- 
ably due in a great measure to erosion, but are less plainly stream-carved 
channels than the deep gorge above Dayton. Since Lake Lahontan during 
its highest stages occupied the valley as far as Dayton, we are safe in con- 



138 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

# 

eluding that the river channel was carved in pre-Lahontan times, and also 
that the lake which occupied Eagle-Carson Valley must have overflowed and 
cut down its channel of discharge so as to drain that Lasin to the bottom 
previous to the existence of Lake Lahontan. We make i his departure from 
our immediate subject for the purpose of showing that the sediments of the 
Eagle-Carson Lake, in which a variety of foot-prints have recently been 
discovered at the Nevada State Prison, are older than Lake Lahontan, and 
probably belong to early Quaternary or late Tertiary times. 

EXPOSURES IN THE CANON OF WAIiKEB BIVEB. 

The Walker River, in its course between Mason Valley and Walker 
Lake, flows through a comparatively narrow valley, which was deeply filled 
with Quaternary lake sediments and is now a desert, sage-brush-covered 
plain, dissected through the center by a cafion eroded by the present stream 
since the evaporation of the former lake. Like the Humboldt, the Truckee, 
and the Carson, the Walker River has exposed sections of Lahontan sediments, 
in which the tripartite division is well displayed. As in the former instance, 
the upper and lower members are fine, evenly laminated, marly-clays, which 
were evidently accumulated in quiet waters, and are separated by a hetero- 
geneous accumulation of sand and gravel that records an interval of low 
water. 

The tendency of current-borne d^is to accumulate in narrow straits 
connecting broad water-bodies has already been discussed in connection with 
the descriptions of the gravel deposits observed in the Humboldt and Truckee 
cations. A gravel embankment similar to those already described occurs a 
few miles northward of Walker Lake and forms the divide between Walker 
Lake and Walker River valleys. In this instance a large embankment was 
built completely across the mouth of the narrow strait that formerly con- 
nected the open waters of Walker Lake and Mason valleys; subsequently 
this structure was cut through by waters flowing from the northward, thus 
revealing a section of the inclined and arched strata in which the gravels 
were deposited. 

A generalized section compiled by Mr. W J McGee, from many detailed 
observations, is reproduced in Fig. C, Plate XXVIII, which represents the 





•7-^-^.:^ ■'.•-- 




,W.7BS^^M 




WJ HtUti. ZM. 



1, O. Ku—fll. tln}l..ffiMl. 



OETAILFD fiECTlON OF 



?FD-WENTS, THUCKEE CANi 



SECTIONS EXPOSED IN WALKER OAJTON. 139 

structure of the Labontan sediments exposed in the cafion walls for a dis- 
tance of 18 miles. The highest point in the section is at the crest of the 
embankment, which crosses the valley and marks approximately the level 
of the highest water stage of the former lake. Between the embankment 
mentioned above and Walker Lake, a distance of 8 miles, the river banks 
vary from zero at the lake to 50 or 60 feet in the neighborhood of the em- 
bankment. In this interval the exposures are almost entirely of upper 
lacustral clays, with intercalated beds of volcanic dust, but at a few locali- 
ties, in the northern portion of the section, the medial gravels and under- 
lying clays may be seen at the base of the escarpment bordering the river. 
Where the stream-channel crosses the embankment, the entire exposure, 200 
feet high, is composed of inclined and arched strata of sand and gravel 
inclosing irregular and loamy beds. The entire series has a characteristic 
pinkish tint due to the presence of iron oxide. This embankment occurs 
unconformably between the upper and lower clays, and, like Inany similar 
structures when seen in section, exhibits anticlinals of deposition. Its base 
is not exposed to view, but as the clays of the lower series occur near at 
hand, both to the north and south, it seems probable that the gravels com- 
posing the embankment were, at least in part, accumulated during the time 
the lower clays were being deposited. Like the embankment at the south- 
ern end of Humboldt Lake, this structure was probably begun early in the 
history of Lake Lahontan, and has been enlarged many times since. The 
last addition was contemporaneous with the deposition of the upper clays, 
or perhaps in part subsequent to it; in the main, however, it is composed 
of the medial gravels of the Lahontan series. Northward from the crest 
of the embankment the canon walls decrease in height, as represented in 
Fig. C, Plate XXVIII, all the way to Mason Valley, where the river becomes 
a surface stream. The medial gravels are exposed for about 8 miles north 
of the embankment, and appear again at a point where they have suffered 
some local disturbance about 4 miles below the point where the river 
leaves Mason Valley. 

Throughout the entire exposure of lower lacustral clays observed in 
the Walker River Cafion, the strata are of light-colored, laminated, marly 
clays, of the same nature as the corresponding beds occurring in the Hum- 



140 GEOLOGICAL HISTORY OF LAKE LAHONTAK. 

boldt and the Truckee canons, and therefore do not require farther description. 
The medial gravels, in common with lacustrine shore deposits in general, 
are heterogeneous accumulations of worn and rounded sand, gravel, and 
boulders, with occasional inclusions of finer debris; cross stratification pre- 
vails, and many of the beds were deposited in an inclined position. 

The upper lacustral clays in the Walker River section are more varied 
and indicate more complex conditions of deposition than the similar expos- 
ures that have been described in the preceding pages. The upper and 
lower portions of the upper clays have the normal features of the deposit, 
but an intermediate portion, varying 20 to 30 feet in thickness, is of a more 
diversified character, and includes strata of sand and gravel which are fre- 
quently iron-stained and in many places form contoi1:ed and folded layers. 

This portion of the upper clays obtained the name of the **bone-bed" 
in our field notes, from the numerous mammalian remains that it contains 
(see Chapter VI). It is exceptional in the Lahontan series, and evidently 
must have been formed under peculiar conditions. The only hypothesis 
which seems to furnish assistance in interpreting the phenomena observed 
assumes that the embankment dividing Walker River and Walker Lake 
valleys formed a dana in late Lahontan times that obstructed the free cir- 
culation of the waters occupying the two basins and caused the region 
above the obstructions to become a swamp or a shallow lake in which the 
iron -stained deposits of varying character containing mammalian remains 
were accumulated. Afterwards the lake rose sufficiently to flood the 
valley and allow homogeneous, fine-grained clays to accumulate. In this 
portion of the deposit the shells of Margaritana margaritifera are abundant. 
The surface of the upper clays over large areas both in Walker Lake and 
Walker River valleys is coated with an abundance of dendritic tufa, which 
occurs both in mushroom-shaped masses that have formed about small 
nuclei and in irregular vertical sheets which penetrate the clays and in 
some instances inclose considerable areas. These sheets of tufa seem to 
have formed on the sides of fissures, or perhaps on eroded surfaces which 
had been submerged, in such a manner as to take an accurate cast of the 
beds against which they were deposited. The upper clays in the Walker 
River section correspond not only in their composition and arrangement 




r. C. BtuarU. niiol«gi$l. 



SECTIONS OF LAHON 



kLKEit fllVEf! CANON NEVADA. 



SECTIONS EXPOSED IN WALKER CAJTON. 141 

with the siniihir beds in other parts of the Liihontaii basin, but they contui!i 
the Siinie species of fossils. Their tufa deposits in various parts of the old 
lake basin record similar chemical conditions. 

The following section observed in the left bank of the Walker River, 
about two miles above the gravel embankment shown on Plate XXVIII, 
represents the prevailing character of the exposures to be seen in this re- 
gion: 



Up{>er lacustral clays 



. . ' 



Feet. 

^-Eoliau deposits fttrmiii^ dt'st»rt surf;u*o 1 to 10 

Lijrbt-colort'd iiiatly rlays. passin}!; into fernigi- 
Dons ttandy bt-ds sttuietimes oontortetl, coutain- 
ing detached iiiaiimialian bones; changing to 
luarlv clavs at the batse 40 to 50 



Contact unconformable. 
Medial gravels Gravels and loam, colored with iron 25 to 30 

Contact unconformable. 
Lower lacust ral clays - . . Light-colored marly clay ; to river 75 

The sections taken at various points along the Walker River show 
great variation, but the differences are caused almost entirely by the want 
of constancy in the medial gravels; the upper and lower members of the 
series are remarkably uniform throughout. In the majority of cases where 
the upper or lower contacts of the medial gravels could be seen they were 
found to be unconformable with the adjacent beds. 

The most difficult problems ])resented by the superficial geology of 
the Walker River Valley are in connection with the orographic disturb- 
ances that have affected the region in post-Lahonta ntimes. The valleys 
occupied by Walker Lake and Walker River are of the Great Basin type, 
and owe their formation to pre Lahontan faulting; the main displacement 
that gave origin to the depressions — which are structurally a single basin — 
follows its western border and determines the extremely precipitous eastern 
face of the Walker Lake or Wassuck Mountains. Other faults, less plainly 
distinguishable, occur on the eastern border of the valley, especially near its 
northern end, and connect with the displacements to be seen in Mason Valley. 
Some of these ancient fault lines, including the largest of all — that following 
the western border of the valley — appear at the surface within the basin of 
the former lake; in such instances a post-Lahontan movement of the ancient 



142 GEOLOGICAL HISTORY OF LAKE LAHONTAK. 

displacements is usually indicated by fresh scarps in lacustral clays and 
gravels. Since the desiccation of Lake Lahontan there has been consider- 
able movement along some of these ancient lines of fracture, and the La- 
hontan beaches and terraces no longer retain their normal position, but in 
places have been carried far above the horizon which they originally occupied. 
If we consider the crest of the gravel embankment separating Walker Lake 
Valley from the valley occupied by Walker River as approximately the 
original level of the Lahontan beach, we find that the eastern end of the 
structure, as determined by Mr. McGee, is now fully 200 feet above its 
original position, as indicated at x', Plate XXVIII. The only explanation of 
this phenomenon the writer can offer is that the fault following the eastern 
border of the valley has increased its displacement in post-Lahontan times 
and earned the shoreward portion of the bar above its normal position. 
Similar disturbances may be seen in the northern part of the same valley, 
where a post-Lahontan fault occurs on each side of the basin exposing char- 
acteristic sections of Lahontan sediments. The altitude of the beach on 
the eastern side of the valley is indicated at x, Plate XXVIII. In the bot- 
tom of the valley and near the northern end, the strata are arched as indi- 
cated in the generalized section. From the limited section open to exami- 
nation, this seems to be a variable anticlinal, and, if so, it is the only post- 
Lahontan arch of this nature that has been observed. The movements 
that produced the disturbances in the northern part of the Walker River 
Valley are connected with the recent displacements to be seen in the vicin- 
ity of the hot springs in Mason Valley, and are so indicated on Plate XLIV. 

Local faults affecting the Lahontan sediments are of frequent occur- 
rence, especially in the lower portion of the Walker River Valley; the throw of 
these displacements is seldom over 40 or 50 feet, and they have caused but 
little change in the topography of the valley. They are of different dates, 
as is illustrated by figures A and B, Plate XXVIII ; in the former, the dis- 
placement took place previous to the deposition of the medial gravels; and 
in the latter, after the upper clays had been deposited. 

We have described the orographic movements in this region in some- 
what general terms, for the reason that it is difficult to describe the facts on 



GENERALIZED SECTION. 143 

which our conclusions rest with as much accuracy as could be desired, and 
also because the subject will claim further attention in connection with other 
orographic disturbances that have aff(3cted the Lahontan basin. 

genp:raij1zed section of j.ahontan sediments. 

On grouping the numerous sections of Lahontan sediments observed 
in the Humboldt, Truckee, Carson, and Walker cafions, we have the fol- 
lowing generalized section of sedimentary deposits formed in the ancient 
lake: 

ATerase ihiokneM, 
mfeel 

Upper lacustral clays : 

Evenly laminated marly clays, fine and homogeneous, usually saline ; with interstratified 

bands of dendritic tufa near the top ; in places containing intercalated layers of yoI- 

canic dust. In some places this member is divisible into three parts, the upper and 

lower beiug normal clays, while the i'it'Crmodiate member is more sandy, and usually 

contains iron-stained lyse, that are frequently contorted 50 to 75 

Fossils : CypriSj Anodontay Margaritana, Sphcerium^ Pitddiuriif Heliaomay Gyraulu9f etc., 

together with mastodon or elephant, horse, and camel. 

Contact uncomformdbU. 
Medial gravels : 

Cross-stratifled sand, gravel, and loam, in beds that are irregular both in thickness and 
inclination, frequently forming arches of deposition. At times exhibiting two plainly 
marked divisions ; the upper beiug a compact, earthy, homogeneous, flood-plain de- 
posit ; the lower clean, well-rounded sand and gravel, at times strongly cross-bedded. . 50 to 200 
Fossils: Anodoniaf GyrauluSf Lymnophysa^ Pompholyx, 

Contact unconformable. 
Lower lacustral clays : 

Laminated marly clays, very similar to the clays at the summit of the section. The clays 

throughout the section frequently exhibit two systems of joints at nearly right angles 

to each other (full thickness not exposed) 100 

Fossils: Pompholyx. 

The interpretation of this section gives an outline of the later Quater- 
nary history of the Lahontan basin ; but as the base of the lower clays is 
nowhere exposed, all the changes that may be recorded by the lower strata 
remain unknown. From the sedimentary deposits observed we learn that 
there have been two high- water periods in the history of the Lahontan 
basin, during which fine clays were deposited. Separating these two periods 
was a time when the lake was low and allowed current-borne gravels to be 
carried far out over the previously formed lake-beds. During the second 
flooding the waters underwent long concentration, and at a certain period 
deposited a vast quantity of tufa ; the lake during this stage also received 



f 



144 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

lai^e quantities of pumiceous dust, which must have been thrown out by 
some volcano in the state of violent eruption. The second rise of the lake 
was followed by the present period of desiccation, which witnessed the 
evaporation of its waters and the exposure of its sediments to subaeria! ero- 
sion. The rivers in flowing across the exposed lake-beds carved the deep 
channels we have described, and are now spreading stream and current 
borne gravels far out in the central portions of the valleys, thus in many 
ways repeating the conditions that characterized the time during which the 
medial gravels were deposited. 

In order to represent the sediments of Lake Lahontan on a geological 
map of the region one has but to color the area once occupied by the lake 
with the appropriate tint. The older rocks throughout the area are not com- 
pletely concealed by the sediments of the lake, however, the exceptions 
occurring along the borders of the basin and about isolated buttes; but these 
portions being usually precipitous, the belt left unconcealed is so narrow- 
that it would be scarcely possible to represent it on a geological map of the 
scales ordinarily used. 

To prevent confusion it seems appropriate to indicate at this time some 
discrepancies that exist between the published reports of the United States 
Geological Exploration of the Fortieth Parallel and the conclusions pre- 
sented in the present volume. On map V of the atlas issued for that explo- 
ration a large portion of Lahontan basin is included. The area covered by 
the sediments of Lake Lahontan, as determined by the present survey, are 
there indicated in four diflerent ways. Some portions are represented as 
Ti-uckee Miocene, others as Humboldt Pliocene, while the greater part is 
divided between Upper and Lower Quaternary. 

The areas colored as Truckee Miocene are situated at the lower end of 
Humboldt Lake and at the southern end of Winneunicca Lake. The de- 
posits at these localities are similar, consisting, if the writer's determinations 
are correct, of gravels that were accunmlated in the form of bars or embank- 
ments through the action of the currents of the Quaternary lake. The 
some deposits about the south shore of Humboldt Lake have been described at 
length in the preceding pt^s (105 to 112), and a detailed map of the area 



DISCREPANCIES IN CLASSIFICATION. 145 

presented on Plate XVIII. The embankments near the south end of Win- 
nemucca Lake are described on page 120. The discrepancy in reference 
to the nature of the gravel deposits bordering Humboldt Lake may be 
seen by comparing the pages referred to above with the description given 
on page 742 of Vol. II of the reports of the United States Geological Explo- 
ration of the Fortieth Parallel. 

The entire area represented as Humboldt Pliocene, on map V of the 
atlas cited, has been considered throughout the present volume as of 
Quaternary age, and as furnishing the most typical exposures of Lahon- 
tan sediments, as will be seen by referring to the descriptions of the Hum- 
boldt and Truckee caftons. 

The areas colored as Lower Quaternary on map V, of the atlas named, 
are mostly playa-deposits; while the areas designated as Upper Quaternary 
are largely covered with alluvial gravel, especially near the mountains, 
but in the broader valleys within the Lahontan area large portions thus 
designated are floored with Lahontan sediments. In the present report 
Upper and Lower Lahontan clays have been recognized ; these might with 
propriety be termed Upper and Lower Quaternary, but cannot be correlated 
with the Upper and Lower Quaternary of King. The exposures of upper 
and lower Lahontan sediments are so limited, occuiTing mostly in cailon 
walls, that they could scarcely be represented on a map of the scale used 
in that atlas, and if mapped they would not agree with the classification of 
the Quaternary there used. As the facts are interpreted by the present 
writer, the lake beds there mapped as Lower Quaternary belong to Upper 
Quaternary, while the playas also mapped as Lower Quaternary are recent. 
The alluvial deposits, there mapped as Upper Quaternary, are deep forma- 
tions whose accunmlation began at least as early as the Tertiary and has 
been continued to the present time: Their surface layers are in part mod- 
em, but other areas have received no recent additions and are superficially 
Upper Quaternary. 

MON. XI 10 



146 GEOLOGICAL HISTORY OP LAKE LAHUNTAN 

EXCEPTIONAL SEDIMENTARY DEPOSITS, 

PUMICEObS DUST. 

In describing the section of upper lacustral clays observed in the 
Humboldt, Truckee, and Walker River cailons, strata of fine silicious 
material, varying in thickness from a fraction of an inch to five or six feet, 
were noted at a number of localities; it is now our intention to describe 
these abnormal deposits more fully. 

In all the exposures of this material the same characteristics were 
observed. The beds are composed of a white, unconsolidated, dust-like, 
silicious substance, homogeneous in composition, and having all the general 
appearance of pure, diatomaceous earth. When examined under the mi- 
croscope, however, it is found to be composed of small, angular glassy 
flakes, of a uniform character, transparent and without color, but sometimes 
traversed by elongated cavities. When examined with polarized light, it is 
seen to be almost wholly composed of fragments of glass, with scarcely a 



2 



A 





8 



\ <^ <^ ^^ a rp^ 




1. Volcanic dnst which fell in Norway, March 29 and 30, 1875. 

2. Volcanic dust emptied from Krakatoa, Angaat 27, 1883. 

3. Volcanic dnat from the Truckee River, Nevada. Quaternary. 

4. Volcanic dost from Brakleast-Hill in Saugna, Mas*}., pre-Carboniferous. 

Fio. 23. -> Volcanic dnst. 

trace of crystal or of foreign matter. On comparison with volcanic dust 
that fell in Norway in 1875, derived from an eruption in Iceland, with the 
dust erupted in Java in 1864, and the similar material ejected in such 
quantities from Krakatoa in 1883, it is found to have the same physical 
characteristics; but it is much more homogeneous, and, unlike the greater 
part of the recent dust examined, is composed of colorless instead of 
brown or smoky glass. In the following figure, which we copy from 



STRATA OF VOLCANIC DDST. 



147 



Mr. J. S. Diller's instructive article on the volcanic sand which fell at 
Unalaska, October 20, 1883/® the microscopic appearance of volcanic dust, 
from various localities and of widely different geologic age, is shown with 
accuracy. The peculiar concave edges and acute points of the shards of 
glass render it evident that they were formed by the violent explosion of 
the vesicles produced by tlie steam generated in the viscid magma from 
which the glass was formed, and were not produced by the mere attrition 
of the fragments during the process of eruption. It is noteworthy that the 
dust erupted from Krakatoa but yesterday is undistinguishable in its main 
characteristics from the material of a similar origin which fell in the waters 
of Lake Lahontan during the Quaternary, or from the dust thrown out by 
some unknown and long since extinct volcano in the vicinity of the Atlantic 
coast, which fell near the site of Boston during pre-Carboniferous or pos- 
sibly in pre-Cambrian time. The volcanic phenomena of to-day are gov- 
erned by the same laws as obtained at the dawn of geologic history. 

Farther study revealed that even the finest of the dust obtained from 
the basin of Lake Lahontan has identically the same physical properties aa 
pumiceous rhyolite forming the Mono Craters, ground in a mortar to a cor- 
responding fineness ; under the microscope the two powders were very similar. 

The dust deposits are rich in silica, as shown by the following analysis, 
by Dr. T. M. Ghatard, of a sample collected in the bank of th6 Truckee 
River near Pyramid Lake; for comparison we give also an analysis, by the 
same chemist, of a specimen of pumiceous rhyolite from the Mono Craters : 



CoDstitaents, etc 



Loes by ignition (water) 

81Uoa(SiO«) 

Alumina (AltOa) and iron (FesOs) 

Lime(CaO) 

Magnesia (MgO) 

Magnesia (MnO) 

Potash (KsO) 

Soda(NaiO) 



Volcanic 
dast 


PamioeooB 
rhyolite. 


8.91 


2.20 


71.16 


74.05 


15.95 


13.85 


0.85 


0.90 


0.41 


0.07 


Trace. 




3.36 


4.81 


4.94 


4.60 


100.67 


99.98 



The striking similarity in the composition of the above samples 
(especially when allowance is made for the greater percentage of moisture 



« Science, Vol. Ill, p. 652. 



146 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

in the specimen of dust, and the fact that it has been exposed to the action 
of solvents much more than the rock remaining in the crater walls) strongly 
favors the assumption that they had a common origin. 

More extended operations in the field revealed that beds like those 
described above are not confined to the Lahontan basin, but are found as 
superficial deposits above the Lahontan beach at many localities and at 
points far distant from the old lake margins. Accumulations of the same 
nature occur in the Mono Lake basin, interstratified with lacustral deposits, 
and were also found in the canons about Bodie at a considerable elevation 
above the level of the Quaternary lake that formerly occupied Mono Valley. 
About Mono Lake these deposits are frequently of a coarser texture thsn 
those found farther northward, and, at times, graduate into strata which 
reveal to the eye the fact that they are composed of angular flakes of 
obsidian. 

The Mono Craters form a range some 10 or 12 miles long, which 
extends southeastward from the southern shore of Mono Lake, and in two 
instances attains an elevation of nearly 8,000 feet above the lake. A few 
coulees of dense, black obsidian have flowed from them, but the great 
mass of the cones is formed of the pumiceous obsidian which occurs both 
as lava-flows and ejected fragments, the latter forming a light lapilli which 
gives a soft gray color to the outer slopes of the craters. Fragmental 
material of the same nature has been widely scattered over the mountains 
and on the ancient moraines that occur in the Mono basin, while fine dust, 
unquestionably derived from the same source, may be traced to a still 
greater distance. 

From the evidence given above we conclude that the strata of fine, 
siliceous, dust-like material occurring in the Lahontan sections, as well as 
the similar beds found about Mono Lake and scattered as superficial 
deposits over the neighboring mountains, are all accumulations of volcanic 
dust, which was probaly erupted from the Mono Craters.^ The greatest 

^This material could not have been erupted from the craters in which the Soda Lakes, iieur 
Ragtown, are situated, as these volcanoes are formed of quite different and more heterogeneous ma- 
terial. The fragments of scoria ejected from these vents are composed of basalt in which grains of 
olivine are conspicuous. 



STRATA OF WHITE MARL. 149 

distance from the supposed place of eruption at which these deposits have 
been observed is about 200 miles. 

The resemblance between the volcanic dust described above and very- 
pure diatomaceous earth is so close that it is difficult to distinguish one 
from the other by a cursory examination; with the aid of the microscope^ 
however, the difference is at once apparent, as the dust seldom shows even 
a trace of any organism mingled with it. 

WHITE MARL. 

At a number of localities in the Lahontan basin there are exposures 
of white, chalky marl which does not appear in the cailon sections we have 
described, but is exposed locally, mostly on the sides of the basin, and 
evidently indicates peculiar conditions of the waters in which it was accu- 
mulated. 

White marls were first observed in the Lahontan basin at the south- 
ern end of the desert valley, which is connected with the Carson Desert 
by the narrow pass in which Allen's Springs are situated; during the 
higher stages of the ancient lake this valley formed a land-locked bay. 
That the waters did not extend through the pass at the southern end is 
shown by a series of barrier-bars at about the horizon of the Lahontan 
beach, which sweep about this portion of the ancient shore in graceful 
curves. These concentric gravel ridges, or barrier-bars, record a gradual 
recession of the waters which once filled the valley, and are especially 
noticeable from the neighboring hills when the slanting, afternoon light 
brings out their symmetric forms in bold relief Modern drainage has cut 
a channel through them in a direction at right angles to their general 
trend, and exposed the following section: 

Feet 

Well-worn gravel, formiDg barrier bars 15 to 25 

Fine Band, cross-bedded 8 to 10 

Finely laminated, white, chalky marl 

Gravel, well rounded, ferruginous Ito 2 

Fine sand ; to bottom of exposure Ito 2 

The marl at this locality is by aneroid measurement 175 feet below the 
Lahontan beach, and may be traced for a hundred yards or more along the 
sides of the arroyo. At both its lakeward and shoreward margin it becomes 



150 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

impure from the intermingling of sand and gravel, and finally wedges out 
and is replaced by water- worn debris like that forming the bars. It seems 
to form a lenticular mass, filling a local basin, but the section does not 
give complete proof that such is the case. Our observations would apply 
equally well to a low oflF-ahore embankment built by gentle currents, and 
subsequently buried by ordinary shore-drift. The gravel bars resting on 
the marl were formed during a subsequent rise of the waters and were 
never afterwards submerged; consequently the marl must have been de- 
posited previous to the last high-water stage of Lake Lahontan '^Fhis will 
be of interest when the oscillations of the lake are more fully described. 

Passing to other localities where white marl has been observed, we 
find that in sheltered ravines on the sides of the basaltic buttes overlooking 
the southern shore of the South Carson Lake there are fine, mealy deposits 
of this nature, 20 or 30 feet thick, and some distances below the highest 
of the Lahontan terraces, which contain gasteropod shells in abundance. 
Similar beds were also observed about 2 miles north of Allen's Springs, in 
the bottom of the ancient channel leading to the Carson Desert. The 
exposure is here imperfect, and as the beds are but little elevated above 
the general desert-surface it is with doubt that they are refeiTed to the 
same period in the history of the lake as the similar deposits observed at 
higher levels. White marl may also be seen at a number of indefinite 
exposures at a uniform horizon, some distance below the Lahontan beach, 
along the steep bluffs which border the Carson Desert on the south. In 
Alkali Valley, 2 or 3 miles west of Sand Springs, similar marls filled with 
gasteropod shells occur in a group of embankments that project into the 
valley. Another locality of the same nature was observed on the west 
side of Humboldt Lake at an elevation of four hundred feet above the 
lake surface. 

In the Truckee Cafion, about a mile below the Truckee Narrows, there 
are beds of pure, white, chalky marl not less than 50 feet in thickness, that 
are grouped about a butte of volcanic rock which was formerly completely 
buried beneath Lahontan sediments, but is now exposed by the erosion of 
the river. These beds are in part overlain by Lahontan deposits, but the 
exposure is obscure and the relation of the marls to the associated clays 



THE WHITE TERRACE. 151 

not easily determined; no fossils were found, and it is not impossible that 
tlie iiinrls nre of much older date than the associated Quateniary beds; 
possibly they are of Tertiary age. 

The best localities of all for observing the deposits we are considering 
are about Pyramid Lake. In this basin they frequently appear as a con- 
spicuous white baud along the borders of the valley at an elevation of 320 
feet above the 1882 level of the lake, and form a well defined built-terrace 
whicli we have named the "White Terrace." Measurements with au engi- 
neer's level, as well as many observations with an aneroid barometer and hand 
level, show tluH terrace to have a nearly uniform height and to be coinci- 
dent in elevation with the water-line which marks the upper limit of the 
deudi'itic tufa. About the Marble liuttes, and at many points along the 
steep western shore of Pyramid Lake, the White Terrace is well exposed in 
sheltered ravines, which were coves and bays wlien the waters occupying 
the valley stood .^20 feet Iiigher tlian at present, but it is wanting on pro- 
jecting spurs. Nortliward of Mullen's Gap the terrace becomes more con- 
tinuou.s, and when cut by arroyos exhibits the sequence represented in the 
following -section : 



'^^:^^^.->-^^^ 




WJti6e J.^u-1- [ 



In some instances tlie outer border of the ternice has been removed so 
that the steep hikoward dip of the strata is not always observable. At a 
number of localities tlie terrace is from 200 to 400 yards broad, with a plane 
or slightly concave upper surface which usually slopes gently lakeward; 
the outer scarp is steep and at times 30 or 40 feet high, but the deposit di- 
minishes rapidly in thickness towards the shoreward margin. The marly 
beds are usually underlain by alluvium, as shown in the figure, and are 



J 52 GEOLOGICAL HISTORY OP LKAB LAHONTAN. 

overplaced along the shoreward margin by similar material that has been 
swept down from the slopes above. Sometimes the marls are deeply eroded 
and present typical " bad land " topography in miniature. 

The White Terrace may be seen at a number of places about the north- 
ern end of Pyramid Lake, and in the pass leading to Honey Lake Valley. 
At the southern end of Smoke Creek Desert it was again observed, with its 
normal elevation of 320 feet above Pyramid Lake. Further northward, it 
occurs at a number of localities on the steep borders of the Black Rock 
Desert. From the numerous exposures observed it is evident that this 
terrace occurs all about the deeper portions of Lake Lahontan, and may be 
considered as co-extensive with the dendritic terrace with which it coincides 
in elevation. The occurrence of the marl as a shore deposit is independent 
of the character of the rock against which it rests ; it occurs with equal pu- 
rity on alluvial slopes and on shores of limestone, basalt, rhyolite, etc. It 
is found in abundance about isolated buttes that formed small islands in the 
former lake, as well as along the shores of the mainland, and is therefore 
evidently not a product of erosion. Occasionally, however, the marl is min- 
gled with sand and pebbles, and when it takes the form of a free bar the 
proximal end will be found to contain more foreign material than the distal 
extremity, thus indicating the assorting power of the currents that trans- 
ported the material. 

At all the numerous localities where the White Terrace is exposed it is 
composed of fine, incoherent, chalky marl, which is often richly charged 
with the shells of fresh-water moUusks. In places the deposit is 40 or 50 
feet thick, and homogeneous throughout. An analysis of a typical sample 
collected on the western border of Pyramid Lake Valley, as reported by 
Dr. T. M. Chatard, is given below, and shows that the material is essentially 
an impure calcium carbonate containing a high percentage of silica : 

Water (HaO) 3.32 

Calcium carbonate (CaCOs) 64. 82 

Silica (SiOs) 22.00 

AlumiDa ( AlgOs) 5. 14 

Iron (FeaOa) 2.04 

Lime(CaO) 0.93 

Magnesia (MgO) 1.89 

100.14 



PC ST QUATERNARY DEPOSITS. 153 

When examined microscopically the marl reveals a great quantity of 
crystallized and amorphous calcium carbonate, very similar in appearance 
to the same substance obtained by precipitation in the laboratory, together 
with other bodies which appear more clearly when the material is treated 
with diluted acid. On examining the residue insoluble in acids under the 
microscope, is found to contain many diatoms, especially in the finer and 
more flocculent portion of the sediment ; the coarser portion, which subsides 
most quickly, also contains diatoms, but is mainly composed of crystalline 
grains and many glassy flakes similar to those composing the volcanic dust 
described on page 146. The chemical and microscopical examinations 
render it evident that the material in question is mainly a chemical precipi- 
tate, but is also, in part, of mechanical and organic origin. 

It seems probable that the calcium carbonate forming the principal por- 
tion of the marl was precipitated from the waters of Lake I^ahontan in a 
microcrystalline and amorphous form at about the time the dendritic tufa 
was being accumulated ; and became mingled with the siliceous exuviae of 
the microscopic organisms that lived in abundance in the lake waters ; it 
also received some contributions of volcanic and aiolian dust, but, in the 
main, was free from the products of ordinary stream erosion. The deposit 
thus formed, when near the shore, was assorted and rearranged by currents 
so as to form the terrace and embankments we now find. In the deeper 
portions of the lake the lime precipitated from the waters was mingled with 
clay and sand and now appears as marly-clay. The abundant precipitation 
near the shore may also have been due, in part, to the greater abundance of 
nuclei which tended by their presence to induce crystallization 

^OXilAN SANDS. 

The accumulations to be described under this head consist mainly of 
sand that has been blown about by the wind and finally deposited in banks 
or dunes which sometimes cover large areas. 

The first acquaintance the explorer in the Great Basin usually makes 
with the material forming these deposits is when it is in motion and fills 
the air with clouds of dust, sand, and gravel, which are blinding and irritat- 
ing, especially on account of the alkaline particles which saturate the 



154 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

atmosphere at such times. Dust-storms are common on the deserts during 
the arid season, and impart to the atmosphere a peculiar haziness that lasts 
for days and perhaps weeks after the storms have subsided. Whirl-winds 
supply a characteristic feature in the atmospheric phenomena of the Far 
West especially during calm weather, as noted already, and frequently form 
hollow dust-columns two or three thousand feet or even more in height, 
which may many times be seen in considerable numbers moving here and 
there over the valleys. The loose material thus swept about at the caprice 
of the winds tends to accumulate on certain areas and forms dunes or drifts 
that at times cover many square miles of surface. During its journey 
across the country the material which finds a resting place in the dunes 
becomes assorted with reference to size and weight, so that the resulting 
sand-drifts are usually homogeneous in their composition, but are character- 
ized by extreme irregularity of structure when seen in section. In the 
Laliontan basin the subaerial deposits are usually composed of fine, sharp 
quartz sand, but in some instances small drifts are principally formed of the 
cases of ostracoid crustaceans. 

A large area buried beneath sand dunes of post-Lahontan date occurs 
a few miles north of Winnemucca and extends westward from the lower 
part of Little Humboldt Valley to the desert between Black Butte and the 
Dofia Schee Hills. This belt of drifting sand is about forty miles long from 
east to west by eight or ten miles in width. The drifts are fully seventy-five 
feet thick and present their steeper slopes to the eastward, thus indicating the 
direction in which the whole vast field of sand is slowly travelling. No 
measurements of the rate at which these drifts advance has been made, but 
their progress is evidently quite rapid, as it has necessitated a number of 
changes in the roads in the southern part of Little Humboldt Valley during 
the past few years. In some places in the same region the telegraph-poles 
have been buried so deeply that they required to be spliced in order to 
keep the wires above the crests of the dunes. The sand is here of a light 
creamy-yellow color, and forms beautifully curved ridges and waves that 
are covered with fret-work of wind-ripples, and frequently marked in the 
most curious manner by the foot-prints of animals, thus forming strange 
hieroglyphics that are sometimes difficult to translate. 



POSTQUATERNARY DEPOSITS. 155 

Another area of driftiDg sand occurs to the southward of the Carson 
Desert and covers portions of Alkah' Valley and the desert basins south of 
Allen's Springs. This train of dunes commences somewhat to the eastward 
of Sand Spring Pass, at the east end of Alkali Valley, and may be traced 
westward for at least twenty miles to the mountains on the east side of 
Walker River Valley. The width of the belt is not more than four or five 
miles. In a sheltered recess in Alkali Valley, a mile or two northwest of 
Sand Springs, the sand has been accumulated by eddying wind-currents so 
as to form a veritable mountain, rising, by estimate, two or three hundred 
feet above the plain. This ever-changing mountain of creamy sand varies 
its contours from year to year, while every zephyr that blows is busy in 
remodeling the rounded domes and gracefully curving crests and in alter- 
ing the details of the tracery that gives grace and elegance to the structure. 
The dunes in this train, like those northward of Winnemucca, are traveling 
eastward across mountains and deserts and seem little afiected in their 
ultimate course by the topography of the country. In the desert valley 
south of Allen's Spring the sand is carried up the steep eastern border of 
the basin and finds temporary resting places on the terraces cut by the 
waves of Lake Lahontan in the black basalt of its shores. The yellow 
sands loading these ancient terraces bring out the horizontal lines in strong 
relief by reason of their contrast in color and accent the minor sculpturing 
of the cliff's. 

Another region of sand dunes covering an area a few square miles in 
extent is located at the southern end of Winnemucca Lake and threatens 
to obstruct the only stream that supplies that water body. 

It is impossible to trace the sands forming these various dunes to their 
sources, but we may be sure that they have traveled far and were not 
derived from the waste of the rocks in their present neighborhood. Similar 
areas of drifting sand occur at many localities throughout the region west 
of the Rocky Mountains, a number of which are known to be traveling in 
the same direction as those of the Lahontan basin. It is possible, as has 
been suggested by previous writers, that these various areas all belong to 
a single series, and are formed of the beach sands of the Pacific which have 



156 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

been blown inland by the prevailing westerly winds. It seems more prob- 
able, however, that they owe their origin to the subaerial disintegration of 
the granites of the Sierra Nevada. 



Section 4.— ANCIENT STREAM CHANNELS. 

When the waters of Lake Lahontan subsided during inter- and post- 
Lahontan periods its basin became divided into separate water bodies or 
independent lakes, some of which were connected by streams that over- 
flowed from one to another. The channels eroded by these streams are 
interesting not only as examples of erosion, but because they contribute to 
the interpretation of the history of the former lake. When a large inclosed 
lake is reduced so far by evaporation that the inequalities of its bottom 
divide it into independent areas, it is evident that this fact in itself is a 
record of an important climatic change; when the ridges or embankments 
that divide a lake in this manner are cut by channels of overflow, it is 
evident that they may furnish some index of the length of the period of 
desiccation or perhaps of the date at which it occurred. The multiplica- 
tion of hydrographic basins by desiccation is illustrated by the present 
condition of the Lahontan region, as shown on Plate XXIX. The ancient 
lake basin is now divided into six independent drainage areas. 

Old channels now abandoned and dry occur in the Lahontan basin, 
between the larger areas of the former lake and the neighboring valleys 
that once formed bays along its shore. The Carson Desert is united with 
the desert valley south of Allen's Springs by a deeply eroded channel of 
this nature, which appears to have been cut by a stream flowing northward; 
a moderate rise of the waters of the Carson Desert would flood this pass and 
reconvert it into a strait This channel is about 5 miles long, and has pre- 
cipitous walls composed of lacustral sediments, which are lined with the form 
of tufa we have called dendritic, while in the bottom of the pass there are 
crags of thinolitic tufa; from these records we learn that the channel was 
excavated previous to the rise of the lake during which tufa deposits were 
formed. As the sequel will show, these tufas were deposited during that 



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ANCIENT STREAM CHANNELS. 157 

portion of Lahontan history that witnessed the accumulation of the upper 
clays; and since the walls of the channel are composed of lacustral sedi 
ments, the inference is drawn that it was excavated during an inter- Lahon- 
tan period of desiccation. It will appear, as we progress with our history, 
that this is but one of a number of independent lines of proof which show 
that Lake Lahontan had two high-water stages, sei)arated by a time when 
it was greatly lowered by evaporation, and perhaps readied absolute dryness. 

The ancient channels, now dry and abandoned, similar to the one con- 
necting Carson Desert and the desert basin south of it, occur at the northern 
end of Pyramid Lake Valley; one of these leads to Honey Lake Valley 
and the other to Smoke Creek Desert. The former, known as Astor Pass, 
was never deeply excavated, showing that the valley in which Honey Lake 
is situated must have been an independent water-body during a large part 
of the Quaternary. The second, however, is a pass, now partially obstructed 
by gravel embankments, which must have been a narrow strait during the 
greater part of the Lahontan period. The bottom of this pass is on a level 
with the thinolite terrace in Pyramid Lake Valley, as shown by aneroid 
measurements, and is thought to have regulated the water in that valley in 
such a manner as to bring it frequently to the same level. This would be 
accomplished by allowing it to escape, at a certain horizon, on to the Smoke 
Creek Desert. It may be that this is the reason for the great strength of 
the thinolite terrace about Pyramid Lake. Another channel of a similar 
character, now known as the Ragtown Pass, connects the Carson Desert 
with the desert valley in which the Eagle Salt Works are situated. All 
these channels were in existence before the deposition of dendritic tufa, but 
the proof that they were excavated in lacustral clays is less definite. It is 
probable that -some of them were occupied by streams before the first rise 
of the ancient lake. In some instances they have become partially re-exca- 
vated during the present period of desiccation, but usually they are still 
occupied ])y the upper clays. 

Other channels of this character have been examined in the Lahontan 
basin, but their features are not so clearly defined as in the examples 
described above, and their bearing on the history of the former lake is con- 
sequently less definite. 



1 58 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



Section 5.—ILLUSTRATI0NS OF GEOLOGICAL STRUCTURE. 

It is customary to consult the older and usually the more thoroughly 
consolidated stratified rocks for illustration of geological structure, but as 
such features are in many cases the records of the manner in which the 
beds were deposited, it is evident that they should occur in the newest as 
well as the oldest formations. It is well known that the history of the earth 
is a continuous record, however fragmentary it may seem at the present 
day, and that the processes of nature have been the same throughout the 
geological ages. Nowhere are these axioms more thoroughly sustained 
than in the recently desiccated lake basins of the Far West. As the gravels 
and finer sediments deposited in Lake Lahontan aflford many instructive 
records of the circumstances under which they were accumulated, we have 
prepared the following brief summary of observations relating to geologic 
structure due to deposition, erosion, etc., believing that it will assist in inter- 
preting similar phenomena when observed in older rocks, where they are 
frequently obscured by metamorphism and other changes. 

STRATIFICATION AND LAMII^ATION. 

The sediments forming the upper and lower portions of the Lahontan 
section consist of fine, homogeneous, evenly-stratified marly-clays, which 
show a distinct lamination parallel with the planes of bedding. Attention 
is called to the lamination of these deposits in connection with other features 
due to deposition, as it has manifestly resulted from the slow accumulation 
of fine sediments in thin layers, and does not owe its existence to pressure, 
as is the case in many older rocks. This is evident since both the upper 
and lower clays are alike laminated, while the higher members of the series 
at least have never been subjected to the pressure of superimposed deposits. 

CURRENT BEDDING. 

The gravels separating the upper and lower Lahontan clays are char- 
acterized by extreme irregularity, and afford many illustrations of structure 
due to deposition. They were deposited in the shallow waters and were 
much agitated by waves and currents, and among other features present 



ILLUSlItATIONS OF GEOLOGICAL STRUCTURE. 159 

typical examples of "current bedding," sometimes called ^' cross- bedding" 
and "false-bedding," as is abundantly illustrated in the walls of the Hum- 
boldt, Truckee, and Walker caiions. The beautiful curves presented by 
these irregular beds when seen in section are represented with much accu- 
racy in the detailed sections illustrating the exposures observed. From the 
thousands of examples examined in various portions of the basin, those 
presented on Plates XXIII, XXIV, XXV, and XXVII, have been selected 
as types of this phenomenon. Not only is this structure remarkable for 
the grace and elegance of the curves produced, but each SAveeping line 
and each cui'ving stratum has an individual structure and varies through 
all degrees of fineness, and through very many shades and tints, which 
serve to distinguish it from adjacent deposits. The accuracy of the illustra- 
tions to which we have directed attention renders farther description of the 
forms presented by current-bedded gravels when seen in section unneces- 
sary. 

Examples of what may be properly designated as "drift bedding" are 
abundant, especially in the walls of the Truckee Caiion, which furnish fine 
examples of the oblique stratification produced when currents sweep sand 
and gravel along the bottom until the edge of a scarp is reached and then 
deposit them in inclined layers. Under favorable circumstances this action 
may continue until a stratum is formed that is obliquely stratified from top 
to bottom, perhaps several feet in thickness, and of wide extent, as illus- 
trated in the central portion of the section exposed in the Truckee Caflon. 

The deposition of current-borne dSbris in inclined strata sometimes 
takes place on a grand scale, as is illustrated by the section of the gravel 
deposits at the southern end of Humboldt Lake, shown in Fig. 17, and 
again by Fig. 20, which represents a section of a similar structure at the 
southern end of Winnemucca Lake. In the cafion of the Walker River, 
evenly-bedded strata inclined at an angle of from 15^ to 20° are exposed 
in a section that is fully 200 feet high, as represented on Plate XXVIII. 
In all these examples, and in many others that have been studied, the 
current-borne gravels composing the strata were deposited in the inclined 
position they now occupy, and do not owe their inclination to a movement 
of the beds subsequent to their deposition. Stratified beds deposited at an 



160 GEOLOGICAL HISTORY OF LAKE LAHONTAK 

incline are usually composed of water-worn gravel, but instances are not 
rare in the Lahontan basin of fine clays and marls that were formed in 
even layers inclined at an angle of from 10 to 20 degrees.- 

* 

CONTORTED STRATA. 

The folded and contorted appearance presented by many sedimentary 
beds may originate in two ways; either the}'' were deposited in a horizontal 
position and subsequently disturbed, or they were laid down in agitated 
waters in the contorted forms we now find. The Lahontan sediments 
afford illustrations of each of these modes of origin. 

Examples of contortion and deformation in the lower lacustral clays, 
obviously due to motion produced by the weight of the superimposed de- 
posits, were observed at many localities. In the Truckee Caiioft, disturb- 
ances of this nature occur, as shown in the lower portion of the illustration 
forming Plate XXV. At the left of the section the stratum of marly clay has 
been broken in an irregular manner and one part thrust over the other; at 
the right, in the same section, the strata are crumpled and folded in such a 
manner as to form anticlinals and synclinals in miniature. Other illustra- 
tions of similar disturbances may be seen in the section exposed along the 
Humboldrt, Truckee, and Walker rivers. At the top of the section shown 
on Plate XXV, but weathered back so as not to appear in the drawing, 
there is a deposit of fine yellowish sand in contorted strata resting on the 
upper clays. This deposit contains crystals and rosette-like masses of 
selenite, and is evidently water-laid — not aeolian as perhaps might be fan- 
cied — and from its position at the top of the section could never have been 
subjected to pressure or mechanical disturbance. The contortions and fold- 
ings of the thin sheets of sand composing this deposit are rendered espe- 
cially distinct, when seen in section, by the presence of iron-stained lines 
and bands, which indicate a character of contortion that can only be ex- 
plained by assuming that the beds were deposited in the irregular forms 
they now present. Similar contorted beds were observed in the Quaternary 
strata of the Mono Lake basin, California, in a bed of sand and pebbles 18 



N 



ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 161 

inches thick, inclosed between horizontal, evenly-bedded, ripple-marked 
clays and sand. In this instance the iron-stained lines marking the edges of 
contorted sheets, form a most intricate pattern when seen in section, and in- 
close pockets and cells sometimes four or five inches in diameter, that are 
without openings and packed full of gravel and stones; in some instances the 
pebbles thus enclosed are an inch or more in diameter and are all well water- 
worn. The presence of these cells filled with material of a different nature 
from the contorted sheets of sand, while the strata above and below the 
contorted layer are of fine sand and clay in even horizontal beds which 
show no crumpling, is evidently proof that the disturbance causing the 
irregularities of the deposit took place during the deposition of the strata 
and cannot be referred to subsequent mechanical movement. The condi- 
tions under which these contorted sands were accumulated are diflScult to 
determine, but in some instances deposition seems to have taken place in 
shallow lakes that were greatly disturbed by winds and currents. The 
hypothesis which attributes the contortion of superficial strata to the action 
of advancing glaciers and grounded icebergs is not here admissible, as the 
relation of the lakes and glaciers is well known. The action of a moving 
ice sheet, formed by the freezing of a lake, might perhaps under certain 
conditions disturb the sediments beneath, and might even transport pebbles 
from the shore and drop them in ofi'shore deposits; thus forming strata 
analogous to the exposure observed near Mono Lake. It is impossible, 
however, to account completely for all the phenomena observed by any of 
the hypotheses that have been suggested. 

ARCHE8 OF DEPOSITION. 

The finest example of an arch of deposition that has been observed in 
the Laliontan s ediments is represented in the section forming Plate XXV, 
and has already been noticed in describing the exposure to be seen along 
the Truckee River. This, with scarcely any doubt, is a section of a gravel 
bar, the top of which was removed previous to the deposition of the 
superimposed gravels. Similar arches, but less complete, may be seen in 
other portions of the Truckee section, and occur in greater or less perfec- 
tion wherever a cross-section of a current-formed embankment or bar is 

MON. XI 11 



162 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

exposed That the arch represented on Plate XXV is the result of depo- 
sition and not of mechanical disturbance is clearly shown by the horizontal 
stratification of the material above and below it 

UI^CONFORMABIIilTY BY EROSION AND DEPOSITION. 

Wherever the junction of the medial gravels with the lower or upper 
clays is exposed, one is nearly always sure to find evidence of unconforma- 
bility, resulting usually from the erosion of the older strata. Examples of 
this phenomenon are shown in nearly all the accompanying illustrations 
which include the junctions in question. Dn Plate XXVII, the cross-strat- 
ification of the gravels filling eroded hollows in the lower clays is admirably 
shown by Figs. A, C, and D. On Plate XXIII, Fig. G illustrates the man- 
ner in which the strata filling eroded hollows are sometimes thickened ; 
while Fig. J shows a thinning of similar beds when deposited over a pro- 
tuberance of the bottom on which they were laid down. Figure K, of the 
same plate, furnishes an example of current-bedded gravels covering the 
eroded surface of the lower clays, while a second line of unconformity, also 
resulting from erosion, parts the gravels themselves. Sometimes the vari- 
ations due to erosion and deposition are complicated by the effects of sub- 
sequent lateral movement, as appears to have taken place in D, Plate 
XXIII. Unconformability by deposition alone, where erosion has but little 
effect, is shown in Fig. B, Plate XXVIII, which illustrates the contact of 
horizontal lacustral beds resting upon gravels that were deposited in in- 
clined strata. Other examples of a similar character may be found in many 
of the accompanying illustrations. 

JOINTING. 

The marly clays forming the upper and lower members of the Lahon- 
tan series usually break into prismatic and cubical blocks on weathering ; 
the vertical faces of the blocks are determined by joint planes, and the hor- 
izontal by planes of lamination. In many localities a more pronounced 
jointing occurs, forming two approximately vertical systems that are nearly 
at right angles to each other. Judging from the number of instances 
observed, at widely separated localities, the joints in question may be 



ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 163 

traced through the entire series of lacustrine beds. The occurrence of 
two distinct and well-marked systems of joints in a bed of marly clay 6 
feet thick, lying between unconsolidated gravels, has been noticed on 
page 132. This may be taken for an example of what may be seen at 
numerous localities. The most striking exhibition of jointing that we 
have observed in the Lahontan strata occurs in the upper clays on the 
west side of the Humboldt River, near Saint Mary's. An arroyo has there 
exposed a vertical cliff 25 feet high, of homogeneous, marly clay that is cut 
from top to bottom by joints which divide the material into small pentag- 
onal prisms that bear a superficial resemblance to basaltic columns. Speci- 
mens of these prisms may be collected that are 2 or 3 feet in length and 
not over 3 or 4 inches in diameter, with sharply-defined edges; in some in- 
stances the diameter of the columns is much less than here indicated, the 
prismatic form being still well preserved. The jointing of the Lahontan 
sediments is of the same nature as the similar phenomena observed in the 
Bonneville basin, the origin of which has been the subject of some dis- 



cussion.^^ 



FAUL.T8. 



Two systems of faults have affected the sediments of Lake Lahontan ; 
the first is of wide extent and due to a recent movement along the ancient 
lines of displacement which gave origin to the structural features of the 
region ; the second is of local origin, and seems to be entirely independent 

of orographic disturbances. Displacements of the first class will be de- 
scribed in a future chapter devoted to the description of post-Lahontan oro- 
graphic movements. The local faults in which we are interested at present 
are common in the soft, unconsolidated sediments of the ancient lake, but 
even in the most typical instances their displacement does not exceed a few 
feet, and, as indicated by several observations, they appear to have small 
vertical range, i. e., their throw diminishes and finally disappears when 

»« G. K. Gilbert, " Post-Glacial Joints," American Journal of Science, Vol. XXIII, 1882, pp. 25-27. G. 
K. Gilbert, '• On the Origin of Jointed Structures," American Journal of Science, Vol. XXIV, 1882, p. 50. 
John Le Conte, **Origin of Jointed Structure in Undisturbed Clay and Marl Deposits," American Jour- 
nal of Science, Vol. XXIII, 1882, p. 233. W. O. Crosby, " On the Classification and Origin of Joint-Struct- 
ure," Proceedings Boston Soc. Nat. Hist., Vol. XXII, 1882, pp. 72-85. H. F. Walling, ** On the Origin of 
Joint Cracks," Proceedings American Association for the Advancement of Science, Vol. XXXI, 1882, p. 
417. 



164 GEOLOGICAL UISTOET OF LAKE LAHONTAN. 

traced downwards. Their hade usually approaches the perpendicular, and, 
as is common witli tlie displacements in older rocks, slopes to the downthrow. 
In tlie instance represented below, however, the hade is reversed ; this ex- 
ample occurs in unconsolidated gravels and clays of the Lahontan series at 
Mullen's Gap, on the western border of Pyramid Lake. 




Tie. 25.— KeTerM Ckult id Laboaton gnvsli. 

The Upward bend of the strata on the heaved side of this fault may 
perhaps be accounted for by assuming that the displacement has undergone 
double movement During the first, the block to the left of the plane of 
fracture, as it appears in the figure, was the thrown block ; its downward 
movement caused the ends of the strata of which it is composed to bend up- 
wards, as is common in similar displacements in older rocks ; afterwards the 
movement was reversed, and what was previously the thrown side was up- 
raised beyond its former position. The faulting took place in this instance 
previous to the deposition of the cross- stratified gravels represented in thii 
diagram above the line of uncuiiformability, as is proven by the fact that 
the plane of fracture does not extend thi-ough them. Tlie interval between 
the. disturbance causing the fault and the deposition of the superimposed 
beds was short, as is evident from tlie absence of erosion along the surface 
of unconformability. 

Another illustration of the minor displacements that occur in the 
Lahontan sediments is given ou Plate XXIII, Fig. A, which is remarkable 



ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 165 

for the narrowness of the block cut out by the double dislocation; this 
double fault is one of a pair, as is shown in the following figure, which is 
drawn to the same vertical and horizontal scale, and represents with con- 
siderable accuracy the exposure observed in the cailon wall. 




This section includes the upper portion of the medial gravels, the 
upper clayK, and the subaerial accumulations forming the surj'ace of the 
desert. 

In the walls of tlie Walker River Cafion, between Mason Valley and 
Walker Lake, there are many examples of faults which shear the lacustral 
deposits of the Laliontan series; two illustrations of the displacements there 
observed are given in Figs. A and B, Plate XXVllI. In the former, the 
actual fault is concealed l)y an alluvial slope, but the dip of the strata 
proves that it was formed previous to the deposition of the upper clays and 
probably before the medial gravels were accumulated. In the latter 
instance (Fig. B) the faulting occurred after the last nse of the ancient lake, 
and affected both the medial gravels and the upper clays. The inclination of 
the strata in the lower portion of this section is mainly due to their having 
been deposited in an inclined position. In tliis instance, as is usually the 
case in tlie faults we are considering, the general inclination of the beds 
due to deposition is but little disturbed. On Plate XVII, Fig. E, a number 
of faults belonging to the class we are considering are represented, which 
cut the stratified lapilH composing tlie ancient craters now occupied by the 
Soda Lakes near Ragtown, Nevada. 

The faults noticed in the preceding paragraphs can only be studied 
to advantage when fresh sections of the Lahontan beds are exposed, and in 



166 (GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

no instance is their presence indicated by a scarp crossing the surface of 
the deserts. 

The existence of faults shearing unconsolidated strata of sand and clay 
can scarcely be accounted for by the hypothesis of tangential strain, as has 
so often been done in the case of displacements in older and more consoli- 
dated rocks, as these beds are still horizontal and have not been subjected 
to the pressure of superimposed accumulations. The strata on either 
side of the planes of fracture are undisturbed. As the displacements are 
local and unconnected with any general orographic movements and in 
some instances die out as we trace them downwards, it seems safe to con- 
clude that they have resulted from some change in the strata them- 
selves, as is perhaps the case also with the joints occurring in the same 
beds. The Lahontan sediments were water-laid and are now desiccated. 
It may be that the contraction produced on drying will be found a suflficient 
explanation of the faulting and jointing that has been observed. The dry- 
ing of heterogeneous stratified beds must result in unequal contraction of 
the various members of the series, at the same time that the unequal desic- 
cation of various portions of the basin would complicate the resultant 
stress. In the Lahontan basin changes of this nature have taken place and 
have been accomplished by jointing and faulting. That these facts stand in 
the relation of cause and effect, however, is but a provisional hypothesis. 

STBUCTUBE OF TERRACES AI^D EMBAlN^^fENTS. 

While describing the formation of terraces and sea-cliflFs it was shown 
that the loose material occurring on lake shores is sometimes swept along 
by currents and deposited so as to form a horizontal shelf bounded by a 
steep scarp on the lakeward slope. Owing to the mode of its formation, 
the structure of such gravel-built terrace is necessarily irregular, but as a 
whole is characterized by oblique stratification, especially on its lakeward 
margin, and abounds in examples of current bedding. Its material varies 
from accumulations of bowlders, sometimes two or three feet in diameter, 
through all degrees of comminution to the finest of silt and marl, and is 
usually of a heterogeneous character, dependent on the nature of the rock 



ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 167 

forming the lake shores. The general structural features of a built terrace 
are shown in the section inserted on page 151. 

When a shore current bearing debris enters deep water, as illustrated 
by a simple instance on page 94, it commences the formation of an embank- 
ment, which is increased by the addition of gi'avel, sand, etc., in inclined 
strata at its end and along its sides. A cross-section of a regularly formed 
embankment should show a series of more or less perfect arches of deposi- 
tion. 

CONGLOMERATES ANI> BRECCIAS. 

In many of the bars and terraces described in this report the gravel of 
which they are composed is firmly cemented by calcium carbonate into a 
compact conglomerate. A similar action has taken place in some of the 
alluvial slopes once submerged beneath the waters of tlie ancient lake, 
which at times has resulted in the formation of typical breccias. On the 
west shore of Pyramid Lake, near Mullen's Gap, the immediate lake margin 
is formed of sand and pebbles that have been consolidated into a firm con- 
glomerate by the deposition of calcium carbonate. Similar beds were 
observed on Anaho Island and about the Needles at the northern end of 
the lake. In all these instances the conglomerate slopes lakewards at a low 
angle, sometimes amounting to ten degrees. This in all cases is evidently 
of a very recent date and in places is still being deposited. Although the 
youngest of the rock series, yet it is suflficiently consolidated to acquire a 
polish from the constant attrition of the sand that is washed over it and 
compact enough to be used for the ruder kinds of masonry. Similar con- 
glomerates which appear also to be still in process of formation were 
observed on the shores of Walker, Winnemucca, and Mono lakes. 

Breccias cemented by calcium carbonate are formed in alluvial slopes 
of the Great Basin above the limits of the Quaternary lakes. These 
deposits are usually less firm than the lacustral conglomerates, and fre- 
quently differ in the fact that the cementing material is accumulated most 
abundantly on the lower surfaces of the stones forming the deposit. The 
precipitation of calcic carbonate in the interstices of alluvial slopes appar- 
ently results from the evaporation of the percolating waters and the conse- 



168 GEOLOGICAL HISTORY OF LAKE LAHONTAK 

quent deposition of the salts held in sohition, which act as a cement and 
sometimes change a loose debris heap to a compact conglomerate or breccia. 
Subaerial deposits of this nature are common throughout the arid region of 
the Far West 

OOLITIC SAND. 

The presence of oolitic sand on the shore of Pyramid Lake has already 
been referred to in connection with the general description of the lake. 
This material is evidently now forming, and in places has been cemented into 
a compact oolite by the deposition of a paste of calcium carbonate between 
the grains, and forms irregular layers several inches in thickness that slope 
lakewards at a low angle. The oolitic grains composing the beach sands 
are frequently a quarter of an inch or more in diameter, and would, per- 
haps, more properly be designated as pisolite. When examined in thin 
sections under the microscope each grain is seen to be made up of a large 
number of concentric layers of calcium carbonate surrounding a particle 
of sand or other foreign body which furnished the original nucleus. The 
spherical form of the grains and the uniform thickness of the concentric 
layers evidently indicates that the kernels were in motion during the slow 
deposition of the concentric shells of which they are principally composed. 
Oolitic sands occur also at a number of localities near the base of the den- 
dritic tufa, thus indicating that the conditions necessary for the formation 
of a deposit of this nature were then prevalent throughout the entire area 
covered by Lake Lahontan. That the chemi» dl conditions favoring the 
formation of oolitic sands vary through wide limits is shown by the fact 
that they are now forming both in Pyramid Lake and in Great Salt Lake. 
The former contains less than half of one per cent, of solids in solution, 
while the latter has varied from over twenty-two to about thirteen per cent 
during the past twenty years.^^ 

SURFACE MARK1]^GS. 

The surfaces of lacustrine deposits when laid bare and subject to des- 
iccation become covered with a net-work of shrinkage cracks and are not 
infrequently impressed with the foot- prints of animals; sometimes, too, the 

"See table of analyses at C, page 180. 



COLOR OF LACUSTRAL SEDIMENTS. 169 

muddy surfaces are pitted by falling rain-drops or covered with ripple marks. 
When the waters again cover such an area, all these records may be concealed 
beneath superimposed strata and thus preserved for an indefinite time. 
They are, in fact, as well suited to become fossilized as the records of a 
similar nature so common among the Triassic rocks of the Atlantic slope. 
The markings inscribed on the surfaces of lake beds are identical with many 
records that are made on the sands and mud along the ocean's shore, and if 
fossilized, would in themselves give no indication of the character of the 
water-body on the borders of which they were formed. 

COIiOR OF liACUSTRAIi SEDIMENTS. 

From the study of the Triassic, Old Red Sandstone, and other forma- 
tions of Europe,^ Professor Ramsay was led to the conclusion that sedi- 
ments deposited in inland waters were usually iron-stained. The reverse 
of this conclusion would probably have been reached had lake deposits 
been first studied in the Great Basin, as all the lacustral beds in that region 
are light colored and seldom show more than a trace of the presence of iron. 
Some of the inclined beds in the Walker River section have a pink tinge, 
due to the presence of iron, while some of the contorted sands we have 
described have a yellowish color. These features, however, are inconspic- 
uous and do not aflfect the statement that the sediment in question are a 
total exception to the rule referred to above. 



RfiSUMfi OF PHYSICAL HISTORY. 

To arrive at a satisfactory understanding of the physical history of 
Lake Lahontan, as recorded in terraces, gravel embankments, deltas, sedi- 
mentary deposits, river channels, etc., it is necessary to combine our obser- 
vations of these phenomena with the records of the chemical history of 
the lake as furnished by tufa deposits and desiccation products, with refer- 
ence, also, to the present physiography of the basin. Before considering the 

'^''Od the Physical Relations of the New Red Marls, etc./' Quarterly JoarDal of the Geological 
Society of London, Vol. XXVII, p. 189. Als « : "On the Red Rocks of England of older date thau the 
Tnas.''idid.,p.241. 



170 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

chemical questions connected with the present study, it may be well to see 
how far our observations relating to the physical history of Lake Lahontan 
can be correlated. , 

The presence of vast alluvial slopes of pre-Lahontan date, on which 
the water-lines of the old lake are traced, leads to the conclusion that the 
climate of the region was arid for a long time previous to the first filling 
of the basin of which we have any definite record, viz., the earlier high- 
water stage of Lake Lahontan. The discussion of this question, however, 
falls more properly in the chapter devoted to the consideration of Quater- 
nary climate. We assume, for the present, that a change from arid to 
more humid conditions caused the Lahontan basin to be filled to the level 
of the lithoid terrace, and to remain at that horizon long enough to enable 
its waves to excavate a broad shelf in the rocky shores. The terraces 
above the lithoid are of subsequent date, as is shown by the section of the 
higher water-lines given on page 103; as there indicated the lithoid terrace 
is frequently a shelf cut in the rock, on which rest the built terraces that 
define the Lahontan beach. At other localities the lithoid terrace is rep- 
resented by gravel embankments that are overplafted by much smaller 
structures of the same character at the level of the highest water-line. 
Cumulative evidence of this nature shows that the lake lingered at the 
horizon of the lithoid terrace for a much longer time than at the higher 
levels. The lithoid terrace and the Lahontan beach thus record two 
independent high- water stages The fluctuations of the lake during the 
interval between the formation of these water-lines cannot be determined 
from the physical records alone, but are not difficult to sketch, at least in 
outline, when the tufas that were precipitated from the waters of the lake 
are considered. Turning to the stratified beds accumulated in the lake 
basin, we find two series of fine lacustral sediments separated by a widely- 
spread sheet of water-worn and current-bedded sands and gravels which 
were evidently deposited in shallow water. This record of two lake 
periods, with a time intervening when the basin was at least as nearly 
desiccated as at the present day, is perhaps the most positive of all the 
chapters of Lahontan history. That the formation of these two deposits 
of lake sediments may be correlated in time with the formation of the 



EfiSUMfi OF PHYSICAL HISTORY. 171 

lithoid terrace and the Lahontan beach remains to be considered in con- 
nection with the chemical study of the lake. 

The great number of water-lines scoring the interior of the Lahontan 
basin shows that the main changes in the history of the lake were accom- 
panied by many minor fluctuations. The absence of an outlet renders it 
evident that the minor oscillations as well as the more permanent horizons 
recorded by the ancient terraces were due to climatic changes, the nature 
of which will be considered in a future chapter. 

From this brief resume it will be seen that the facts in the physical 
history of the lake can be correlated but imperfectly, yet give evidence 
that they have a definite sequence and are in fact fragments of a connected 
history. In the chemical studies which follow we shall be able to present 
some of the pages that are here missing and sketch the history of Lake 
Lahontan with greater completeness. 



CHAPTER V. 
CHEMICAL HISTORY OF LAKE LAHONTAN. 

Sbotion 1.— general CHEMISTEY OP NATUKAL WATEES. 

The investigation of the chemical history of a lake properly begins 
with the study of the meteoric waters that supply its hydrographic basin. 
Lakes are filled to some extent by direct precipitation from the atmosphere, 
but mainly by tributary streams and springs; it is evident, therefore, that 
we should look to these channels for the sources of the dissolved mineral 
matter which all lakes contain. It is true that lakes are sometimes formed 
by the isolation of portions of sea water, or may occur over beds of salt or 
other easily soluble rocks; but such cases are exceptional and their abnor- 
mal character easily accounted for. 

BIVEE WATBS. 

Even rain water and freshly fallen snow are not absolutely pure, but 
usually contain some organic and saline matter, together with carbonic 
acid, nitrogen, ammonia, chlorine, etc., which have been dissolved during 
their passag^e through the atmosphere. .In an arid r^on, like the Great 
Basin, where the soil is commonly alkaline, and its surface frequently coated 
over large areas with saline efflorescences, the dust that is carried high in 
the air by the winds is richly charged with soluble salts which are dis- 
solved by the falling rain, thus rendering it less pure than the meteoric 
waters of more humid regions. Rain water on reaching the earth dissolves 
the more soluble minerals with which it comes in contact and becoming 
charged with carbon dioxide (carbonic acid), together with humic and 
crenic acids, and other organic products, it forms such an energetic 8olvet>< 



/ 



CHEMISTRY OF NATURAL WATERS. 173 

that but few substances can entirely resist its action. By the time the sur- 
face waters have united to form rills, they contain sufficient mineral and 
organic matter to have a complex chemical composition. On through their 
history, as they form brooks, creeks, and rivers, and finally merge with the 
ocean or some inland sea, they are constantly increasing their sum total of 
dissolved mineral matter, and are at the same time concentrated by evapo- 
ration. The waters of a river when filtered from all suspended matter and 
evaporated to dryness leave a solid residue which is the principal portion 
(the more volatile substances escaping) of the foreign matter held in solu- 
tion. These waters are fresh in the every-day use of the term, but in fact 
owe their pleasant taste and, to a great extent, their health-giving qualities, 
to the mineral substances held in solution. In the following table the an- 
alyses of the waters of a number of American rivers are given, for the pur- 
pose of indicating what salts are contributed to lakes in greatest abundance 
by their tributaries. The principal impurities in nearly every instance are 
calcium and carbonic acid, probably combined in the waters as calcium 
bicarbonate; sometimes, however, calcium sulphate is in excess of any 
other salt, as in the case of the Jordan River, Utah. Surface waters derive 
their chemical impurities mainly from the rocks over which they flow, and 
consequently vary in composition with the geological character of their 
hydrographic basins. When draining a granitic or volcanic area they are 
usually rich in potash and soda; when flowing over limestone they are fre- 
quently saturated with calcium carbonate. This is illustrated in the Far 
West by the streams entering the Bonneville and Lahontan basins In the 
former they have their sources in the Wasatch Mountains where limestones 
occur, and are usually rich in calcium carbonate; potash is commonly ab- 
sent, and soda, if present, is comparatively small in amount. In the Lahon- 
tan basin volcanic rocks predominate and the streams contain a higher 
percentage of potash and soda than is usual in a region underlain by sedi- 
mentary rocks. 

By inspecting the table it will be seen, as stated above, that the most 
abundant of all the various substances canned in solution by the streams of 
this country is calcium carbonate. On averaging the amounts given in the 
tables we have 0.15044 part per thousiind as the average of total solids, 



174 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

and 0.056416 part per thousand as the average of the calcium carbonate 
contained in the waters of American rivers. 

In a table of 48 analyses of European river waters given by Bischof," 
the average of total solids is 0.2127, and the average of calcium carbonate 
0.1139 part per thousand. From the analyses of 36 European river waters 
published by Roth,^ including some of those tabulated by Bischof, we ob- 
tain 0.2033 part per thousand as the average of total solids; and 0.09598 
parts per thousand as the average of calcium carbonate. In both Ameri- 
can and European river waters, so far as can be determined from the data 
at hand, the average of total solids in solution is 0.1888, and the average of 
calcium carbonate 0.088765 part per thousand. These figures may be 
assumed to represent the average composition of normal rivers. It will be 
noticed that the average for calcium carbonate amounts to nearly one-half 
of that for total solids. 

Knowing the volume of a stream and the percentage of mineral matter 
it holds in solution, we can ascertain the amount of dissolved matter that 
it contributes annually to the ocean or enclosed lake to which it is trib- 
utary. To one unfamiliar with such investigations the amount of solid 
matter thus annually transported in an invisible state from the land to the 
sea will appear truly astonishing. 

The Thames at Kingston, as determined by the Royal Rivers Pollution 
Commission of Great Britain, has an average daily flow of 1,250,000,000 
imperial gallons; the water contains of inorganic impurities 19, and of or- 
ganic and volatile 1.68 grains per gallon. This is equivalent to 3,364,286 
pounds, or 1,682 tons (of 2,000 pounds each), of inorganic matter daily; of 
this two-thirds, or 1,121 tons, are calcium carbonate, and 271 tons calcium 
sulphate. 

The average flow of the Croton River, which supplies New York City, 
is 400,000,000 gallons daily, which contain 365,428 pounds; or nearly 183 
tons of impurities; of these 47 tons are calcium carbonate.^ 

^Chemical Geology, English edition, London, 1854, Vol. I, pp. 76 and 77. 
» Chemical Geology, Berlin, 1879, Vol. I, pp. 456 and 457. 
'^Bep. American Public Health Aasociation, Vol. I, p. 554. 



CHEMISTRY OF NATURAL WATERS. 175 

. The Hudson carries daily about 4,000 tons of matter in solution, of 
which more than 1,200 tons are calcium carbonate.^^ 

The Mississippi, as determined by Humphreys and Abbot,*® discharges 
annually 21,300,000,000,000 cubic feet of water; from the analyses of 
the water at New Orleans, by Dr. W. J. rlones,^^ we learn that the total 
of solids carried annually by the river amounts to 112,832,171 tons; of 
of which fiO, 158,1G1 tons are calcium carbonate. The amount of sediment 
transported by the river annually, as reported by Humphreys and Abbot, 
amounts to 887,500,000,000 pounds or 443,750,000 tons. The amount of 
solids, both in solution and suspension, carried annually to the sea, as deter- 
mined from the data indicated above, is approximately 556,600,000 tons. 
From the very incomplete observations on the discharge of the Hum- 
boldt River that have been made, we will assume 500 cubic feet, or, for 
convenience, 1,700 liters per second, as representing its average flow; each 
liter contains 3615 gram of solid matter in solution, which gives an an- 
nual transportation of about 18,000 tons; of this amount somewhat less 
than one-third, or approximately 5,000 tons, is calcium carbonate. In the 
same general manner we have estimated that the Carson, Truckee, and 
Walker rivers, collectively, transport annually about 10,000 tons of cal- 
cium carbonate. Not to overestimate we will assume that all the streams 
now entering the Lahontan basin carry annually 10,000 tons of calcium 
carbonate in solution. This estimate, although made on very imperfect 
data so far as the measurements of the streams are concerned, is certainly 
not too high, and enables one to understand whence the immense amount 
of calcium carbonate deposited in the form of tufa from the waters of Lake 
Lahontan was mainly derived. 

SPRING WATER. 

All the rain that falls does not find its way directly into the surface 
drainage, but a large portion sinks into the earth, and in many cases has 
a long underground passage before coming again to the light. During its 
subterranean course it takes an additional quantity of foreign matter into 
solution, and has its solvent power augmented by becoming more or less 
thoroughly charged with certain substances, such as carbon dioxide, which 

^'Report of the American Public Health Associatiou, Vol. I, pp. 54^-^43. 
** Report on the Mississippi River, p. 146. ^See Table of Analyses A. 



176 GEOLOGICAL HISTORY OF LAKE LAHONTAK. 

act as solvents for many minerals otherwise not easily dissolved by water. 
Its solvent power is also augmented by the increase of temperature and 
pressure which it undergoes as it descends into the eaith. The waters 
issuing as springs, frequentlj'^ with a high temperature, are almost invaria- 
bly found to have dissolved a great variety of mineral • substances. In 
many instances the less soluble minerals occurring in spring waters are 
held in solution by the presence of carbon dioxide, or by high temperature 
or pressure. When such waters reach the surface they lose a large part of 
their dissolved gases, pressure is relieved, and they are rapidly cooled; 
the result is that much of the mineral matter they contain is deposited 
about the orifices through which they discharge. The substances most 
commonly precipitated imder such conditions are calcium carbonate, oxides 
of iron and of manganese, calcium sulphate, and silica. Accumulations of 
these substances are frequently of great extent as may be amply illustrated 
in any of the hot-spring regions of the world. Only a portion of the dis- 
solved matter brought to the surface by springs is thus deposited, however, 
and in many cases no immediate precipitation takes place. The waters, 
after losing their dissolved gases and becoming cooled, are usually much 
richer solutions than ordinary river waters, and, on joining the surface 
drainage, contribute large quantities of mineral matter to the neighboring 
streams. The solvent action of subterranean waters is frequently indicated 
by the porous and cellular character of certain rocks, as well as by the 
caves, frequently of vast size, that occur, especially in limestones. 

The analyses of river waters in all ordinary instances must exhibit the 
combined result of the solvent action of both superficial and subterranean 
drainage. Springs frequently rise in the bottom of lakes or beneath the 
sea and thus contribute directly to the solutions with which rivers eventu- 
ally mingle. In the case of inclosed lakes, the reaction of mineral waters, 
rising in dense saline solutions, is followed by interesting results, some of 
which will be considered in describing the tufa deposits of Lake Lahontan 
{postea page 221). 

In illustration of the chemistry of natural waters we have compiled the 
following table (B) showing the composition of a few of the better known 
American springs and artesian wells; by comparison with Table A, the greater 
richness of subterranean waters over surface streams is at once apparent. 



Hnmboldt 

Battle Mt., 

Nev. 

Deo., 1872 


Tniokee 

Lake Tahoe, 
Nev. 

Oct., 1872 

F. W. Clarke . 
AnU, p. 42.... 


Walker 

Maaon Valley, 
Nev. 

Oct., 1872 

F. W. Clarke . 
Ante, p. 46... 


Jordan 

Utah Lake — 

Nov.. 1873 


Mohawk 

Utica,N. Y... 


Genesee. 

Rochester, N. 
T. 


T.M.Chatard. 
Ante, p. 41 — 


F. W. Clarke . 
Bulletin Nu. 9. 

U. S. Geol. 

Sarv., p. 29. 


C.F. Chandler 
Johnson's Cy- 
clopedia, Vol. 
IV. 


C. F.Clinndler. 
Johnson's Cy- 

clopedia,Vul. 

IV. 


.0467 
.0100 


.0073 
.0083 
.0093 
.0030 
.0023 
t.0287 
.0054 


.0318 
Trace. 
.01128 
.0038 
.0181 
t.0576 
.0284 


.0178 


.0036 
.0009 
.0318 
.0069 
.0023 
.0569 
.0187 


.0044 
.0023 


.0489 
.0124 
.0075 
t.l544 
.0477 


.0558 
.0186 
.0124 
.0608 
.1306 


.0417 

.00896 

.0024 

.0046 

.0431 














.0320 
.0013 


.0137 


.0225 


.0100 


.0067 


.0014 














.•••>• *••••. ..». 








.0013 


.0014 


























• 




.••••• ....v..... 






























































.0234 


.0250 
























.3615 


.0730 


.1800 .3060 .1525 


.19526 



mce. 



I. 

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ake Owen's 
Lake, CaL 



155 

it.*.' 

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M. 
90 



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14 



DO 



71 



L051 

O. Locw 

AppcutlixJJ 
Alio. Jtep. 
Chief En- 
gi nee I'M, 
lhT6, p. 100. 



21.650 
2.751 



Pyramid 
Luko, t 



Aug., 18F2 



Sevier Lake, 
Utah. 



1872... 



F\V. Clarke O. Loew ... 
Ante, pp. ^1 U. S. Siirv. 



and 58. 



Trace. 
Trace. 
Trace. 



13. 440 



13. 140 
0.3G2 

Trace. 
Trace. 
Trace. 

.164 
Trace. 



1.1706 
.0733 



VV 100 M., 
VoL III, p 
114. 



Walker 
L a k e, I 

Nev. 



1.003 
Sont.. 1>:82 
F.W. Clarke 
Ante, p. 70 



"Winnemncca Van Lake. 
Lake, Nev. 



Aral Sea. 



28. HO ' . 85535 

Tiace. 



.0089 
.0797 



.118 
2.600 



1.4300 



.4090** 
.1822 



45. 500 



0.345 



.0334 




.02215 
.03830 



l.OOl 
Ang.. IH82 
F. W.Clarke Chnncourtoia . 
A n(e, p. (>3. 




Biachof 8 
Chemical 
G e o 1 ogy. 
Vol. I, p. 
04. 


Koth Chem- 
ical Geol- 
ogy, p. 
4G5. 







& 50*J§ 
.246 



.0196 
.0173 






1. C934 



. 47445** 
. 52000 



00750 



3458** 
.1333 



.0275 



.1575 



Trace. IT 
5.693 



6.267§ 
2.555 



.180 



2. 4512 
.0584 
.0022 
.4581 
.5965 



.0008 

8.8386 

.0029 

.0018 

3.3368 

.0011 
Traoe. 



.0032 



Kide. 



86. 403 



2. 50150 



3. 6025 



22.000 



** Carbonic acid by difleuoe. 



Trace. 
Trace. 



10. 8416 



\ 



I 



CHEMISTRY OF NATURAL WATERS. 



177 



To illustrate still further the complex character of the mineral matter 
impregnating spring waters, and at the same time to indicate the changes in 
composition to which springs are subject, we give below two analyses of 
the waters of the same spring collected at different seasons. The sample 
obtained in October was secured after a rain that followed a long dry pe- 
riod, and probably owes its greater richness to saline efflorescences accu- 
mulated in the interstices of the rocks during the arid season and redissolved 
by the percolating rain water : 

Rockbridge Alum Spring No. 4, Rockbridge Countifj Virginia.^ Analyses hy Prof. M. H, Hardin. 

[Beported in grains of anhydrons conBtituonts in one U. S. gallon.] 



Con8titaent8. 



Arsenic 

Antimony 

Lead sulphate) 

Copper Rulphato 

Iron persulphate — 
Iron protosulphate . . 
Man^nnese sulphate. 

Nickel sulphate 

Colbalt Aulphato 

Zinc sulphate 

Aluminum «iulphate . 
Calcium sulphate — 
Magnesium sulphat<'' 
Potassium sulphate . . 

Sodiujn sulphate 

Lithium sulphate* — 
Free sulphuric acid . . 

Silicic arid 

Sodium chloride 

Calcium [ihosphate . . 

Calcium fluoride 

Ammonium nitrat<o . . 
Organic matter 



Collecte<l 
Juno 9, 1872. 



Collected 
October 25, 1872. 



0. (H)IGI 

trace. 
U. 87962 
0. 51527 
0.05433 
0. 03835 
0. 05225 
18.90005 
0. 35228 
1.50165 
0. 06278 
0. 00876 
0. 01790 
2.53866 
1.92591 
0. 14246 

trace. 

trace. 

trace. 

traca 



trftce. 

trace. 

traoe. 
0.10370 
2.90122 



1. 37352 
0.22371 
0. 08124 
0. 21748 
72. 37335 
2. 31527 
7. :i6110 
0. 17586 
0.03463 
0.03241 
3.06633 
4. 38346 
0.14246 
0. 05174 

trace. 

trace. 

trace. 



27. 09088 ! 



Specific ^mvity at 60° Fahr 

Cubic inchcH of gtiHe.s in gallon of wHt4'r : 

Carbon dioxide 

Oxygen 

Nitrogen 



l.(M}04 



not determined, 
not determined, 
not det4>rmincd. 



94.83748 
1.00174 

12.73 
1.04 
4.12 



Temperature of spring 54.5<5 Fahi 



Springs of even more complex composition than the example given 
above might be presented if desired ; in fact, subterranean waters are so 



«>AmericaD Chemist, 1884, p. 247. 



MoN, XI— 12 



178 GEOLOGICAL HISTUIIY OF LAKE LAHONTAN. 

nearly a universal solvent that all known mineral subetanctis may be ex- 
pected to occur in tbem. The recently discovered elements caesium and 
rubidium were first obtained by Bnnsen in the mineral waters of Durkheim 
and Baden-Baden. It is to be lioped that a more minute examination of 
the springs of this country may lead to a similar increase in our knowledge 
of the constituents of the earth. 

OCEAN WATEBS. 

Rivers with their loads of mineral matter in solution, derived both from 
surface and subterranean drainage, commonly flow into the ocean and are 
evaporated. The water rising in invisible vapor from the ocean's surface is 
again condensed, and much of it falls on the land as snow, rain, and hail, 
thus completing the cycle of changes. The mineral matter contributed to 
tlie ocean in solution, together with the substances dissolved directly from 
the bottom and sides of the oceanic basins, remains when the waters evap- 
orate, and tends to increase the salinity of the sea. The precipitation of 
mineral matter from the waters of the ocean or its assimilation during the 
growth of plants and animals need not be considered at this time. 

The results of chemical investigations, particularly those of Forchham- 
mei- and the chemists of the Challenger Expedition, have shown that the 
composition of the total solids dissolved in sea water from all portions of 
the ocean — excepting in the immediate vicinity of the land or near the 
mouths of large rivers — and for all depths, is remarkably constant. Disre- 
garding the presence of the rarer substances, Dittmar gives the average com- 
position of the solids dissolved in sea water as follows:" 

ChloriikofNOiliiini 77.^)8 

Chloride ol'iuagneHiiim 10,678 

Sulpbato of iLiitjj;iie8ia 4.737 

SulphaU'iif limi- 3.600 

Sulphatuorpulimli 2.4«S 

Broniido of luu^ncaiiiiii 0. <!17 

Uarbouatttoflime 0.346 

Total salts 100.000 

A table giving the composition of the waterts of the ocean at many 
localities, as determined by Professor Forchhammer,'* is introduced here for 

'■ThB Voyage of U.M. S. Ckilloiigfr. Pli.vt.i.8 ami Cbwiiislrj, Vol.I,p.a04. 
" Philusophiual Traaaactious of tlm K»,vul Suviuty uf Lundon, Vol. CLV, p. 2S7. 



A 



l> 



CHEMISTRY OF NATURAL WATERS. 



179 



comparison. It shows not only the average composition of the great bulk 
of the waters of the globe, but illustrates one of the most important stages 
in the history of natural waters. 



Compari9(m of the means of all regions of the ocean (German Ocean, Eaitegaty BalHo, Mediterranean, and 

Black Sea excepted), 

[Expressed in parts per thoiusiid.] 



BegioiL 



The AUantio between the equator and N. 
latsoo 

The Atlantic between N. lat. 30o and a line 
tnm the north point of Scotland to New- 
foundland 

The northomnioAt part of the Atlantic 

The East Greenland currt-nt 

Davis Stroita :ina Baffin a Bay 

The Atlantic between thoequatornnd S. lat. 
80O 

The Atlantic between S. lat. '30° and a line 
from Cape Horn to the Cape of Good Hope. 

The ocean between Africa, Borneo, and Ma- 
lacca 

The ooe;in between the southeast coast of 
Asia, the East Indian and Aleutic islands 

The ocean between the Aleutic and the So- 
ciety islands 

The Patagonian cold-wutor current 

The Sonth Polar Sea 



Chlorine. 



Mean 



20.084 

19.828 
19. 518 
19.458 
1&379 

20.150 

19. 376 

iafl70 

18.402 

19. 495 
ia804 
15.748 



Salphnric 
acid. 


Lime. 


2.848 


a606 


2.389 


0.607 


2.310 


0. 528 


2. 329 




2.208 


0.510 


2.419 


0.586 


2.813 


0.556 



MagBMift. 



Allialta. 



2.220 



2.201 
2.160 



2.064 



86.258 



85.083 
85.891 
85.278 
88.281 



2.208 I 86.568 



1&999 



2.247 

2.207 

2.270 
2. 215 
1.834 



2.258 



0.557 

0.563 

0.571 
0.541 
0.498 



0.550 



2.160 

2.055 

2 027 

2.156 
2.076 

1.731 



2.096 



85.088 

33.868 

83.506 

35.219 
33.966 
28.565 



34.404 



It is evidently difficult, if not impossible, to obtain an accurate average 
of the composition of the ocean in all latitudes and at all depths, but a con- 
venient approximation to the truth may be reached The mean of 34.404 
parts per thousand, given in the above table, is the result of a very large 
number of analyses, but includes regions of high northern and high south- 
ern latitude, where the sea must be somewhat aflfected by the melting of the 
great glaciers of these regions. It seems questionable, therefore, whether 
the mean given above is high enough to be taken as the average salinity of 
the ocean. Leaving out the analyses of the waters of Davis Strait and of the 
South Polar Seas, we obtain a general average of 35.101. From 134 analy- 
ses of waters from various parts of the open ocean, given in Roth's Chem- 
ical Geology, the general average of 34.957 parts per thousand was ob- 



180 GEOLOGICAL HI8TOEY OF LAKE LAHONTAN. 

tained. Dittinar states^ that of 160 analyses of sea water collected by the 
Challenger Expedition — 

Parts per thoasand. 

The loweat (from the doutbern pait of the Indian Ocean, south of 66^ S. lat.) coutained 33. 01 

The groateBt (from the middle of the North Atlantic, at ahoat 23^ N. lat.) contained 37. 37 

Average 35. 19 

In general, therefore, we may assume 3.5 per cent, as the average of 
total solids in sea water. 

Besides chlorine, sulphuric acid, calcium, magnesium, and sodium, 
which make up ^ of the total salts dissolved in the ocean, the investiga- 
tions of Forchhammer and others have demonstrated the presence of 26 
elements in solution, including bromine, iodine, flourine, phosphorus, 
silicon, boron, silver, gold, copper, lead, zinc, cobalt, nickel, iron, manga- 
nese, aluminium, magnesium, strontium and barium. Many of these are 
present in extremely small quantities, and have only been detected by the 
aid of the spectroscope ; while the presence of others has been determined by 
indirect analysis. As methods of research become more refined, and larger 
bodies of water are dealt with, it is to be presumed that more of the ele- 
ments entering into the composition of the earth will be found dissolved in 
the waters of the ocean. 

The following comparison of the composition of ocean and river waters 
is from Roth's Chemical Geology ; the figures represent the mean of a large 
number of analyses, and give percentages of total solids : 



ConstitaentA. 



a. Carbonaten . 

b. Sulphates — 

c. ChlorideH — 

d. Other inatt4<r. 



Ocean water. 



River water. 



0.21 
10.34 
89.45 



River water 
in regard to , 
a, b, and e 
only. 



60.1 
9.9 
5.2 

24.8 



80 
13 

7 



This comparison indicates the result of a very complicated series of 
changes, dependent upon both biological and chemical reactions, which 
occur when river waters are subjected to the process of concentration that 



•*» Voyage of H. M. 8. Challenger, Chemistry and Physics, Vol. I, p. 201. 



CHEMISTRY OF NATURAL WATERS. 181 

takes place in the ocean. As shown in the table, the carbonates mostly 
disappear, the sulphates increase slightly in percentage, while chlorides 
(mostly common salt) become the characteristic ingredient. 

WATERS OF INLAND SEAS. 

When rivers empt)' into a basin that has no outlet, their waters are 
evaporated in the same manner as in the ocean, and both their mechanical 
and chemical impurities are left as additions to the filling of the depression. 
Examples of such areas of interior drainage are well known in various 
parts of the world. In southern Asia, the Caspian, Aral, Dead Sea, and 
many other saline lakes, are the evaporating basins for independent hydro- 
graphic areas. The region of the Sahara in northern Africa is also shut off 
froiu the general oceanic circulation, but, owing to tlie high mean tempera- 
ture there prevalent, the surface waters are mostly dissipated before lakes 
are formed. In South America another basin situated in the elevated table- 
lands of Peru and Bolivia is without drainage to the ocean. In North 
America there are small areas of a similar nature in Mexico; but the typ- 
ical example on this continent is furnished by the Great Basin. Man}^ of 
the lakes and seas situated in these various interior basins are without out- 
let, and are highly charged with saline matter. In some instances the per- 
centages of the most abundant salts have reached their points of saturation 
and precipitation is taking place. The greater density of many inclosed 
lakes as compared with the ocean is due to the fact that concentration has 
been greatest in the restricted basins The paucity of animal and plant life 
in most inclosed lakes has also some slight bearing on the problem. 

To facilitate the comparison of the inclosed lakes of this country with 
similar waters elsewhere, we introduce a somewhat extended table of 
analyses of this class of lakes, embracing all within the United States the 
composition of which is known. This table includes the densest of natural 
waters and exhibits the extreme of a series that commenced with the nearly 
pure water formed by the condensation of atmospheric vapor. 

When inclosed lakes were first studied it was quite naturally supposed 
that their usual saline condition could only be accounted for by assuming 
that they were isolated bodies of sea-water which had been shut off from 



182 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

the general area by an elevation of the land. This hypothesis has been 
mostly abandoned, however, as one lake after another has been studied, 
until at the present time it is difficult, if not impossible, to point to a single 
lake, excepting perhaps the Caspian, having such a historj'. The origin of 
the salt lagoons found on so many shores is not here included, as their mode 
of formation is too obvious to admit of their being confounded with inland 
seas. 

SUCCESSION OF SALTS DEPOSITED UPON EVAPOBATION. 

As already seen, inclosed lakes are constantly receiving additions from 
streamy, springs, and rain, but do not overflow, their influx being counter- 
balanced by evaporation. This assures us that their percentage of saline 
matter must increase. This process continuing, a point is eventually reached 
when the waters are saturated with one or more of the more abundant 
salts and precipitation commences. Very simple experiments suffice to 
prove that waters of complex composition, when subject to slow evapora- 
tion, do not deposit their salts in a homogeneous mass, but in successive 
layers or strata of varying composition. As the order in wliich different 
salts are deposited varies with the composition of the waters, it is safe to 
say that in no two lakes is the succession of saline deposits formed on 
evaporation apt to be identicaL Disregarding for tlie present the reactions 
of the various salts upon each other, it is evident that in the evaporation of 
natural brines the order in wliich the contained salts will be deposited is 
.inversely as the order of their solubility. For example, a salt that requires 
a large amount of water for its solution, or, in other words, is sparingly 
soluble, will reach its point of saturation and commence to crystallize out, 
as evaporation progresses, previous to the deposition of a more soluble salt. 
To illustrate, it has been found that calcium carbonate requires about 10,000 
times its weight of water, saturated with carbon dioxide, for its solution, 
while calcium chloride is very deliquescent and dissolves in nearly its own 
weight of water. In inclosed lakes to which streams are contributing these 
salts in equal quantities, and in which evaporation equals or exceeds the 
supply of fresh water, it is evident that the calcium carbonate would reach 
its point of saturation and commence to separate long before the waters had 



SALTS DEPOSITED ON EVAPORATION. 183 

become rich in calcium chloride. In fact, owing to its deliquescent nature, 
natural evaporation seldom proceeds far enough to cause the precipitation 
of the chloride. The early deposition of calcium carbonate when nat- 
ural waters are evaporated is rendered the more certain for the reason that 
it is by far the most abundant salt found in surface waters. 

The fact that various salts are deposited in a regular succession when 
mineral waters are evaporated, is of great service in securing certain ones 
in a pure state by the method of fractional crystallization. In evaporating 
the brines of Syracuse the precipitation of ferric oxide and calcium sulphate 
is first secured by moderate concentration; the water is then conducted to 
lower vats and evaporation is continued until the sodium chloride has mostly 
crystallized. The mother liquor, rich in magnesium and calcium, is tlie^i 
allowed to go to waste. In the Soda lakes near Ragtown, Nevada, sodium 
and calcium carbonates crystallize out as the mineral gaylussite, by the 
natural concentration of the waters; when evaporation is continued, the 
deposition of sodium sulphate and carbonate takes place previous to the 
crystallization of common salt. 

On concentrating sea water it has been found that calcium carbonate 
is usually the first constituent to be precipitated. This salt is not always 
found when the waters of the ocean are analyzed, but may usually be de- 
tected when the sample examined is taken near shore. The quantity deliv- 
ered to the ocean by the drainage of the land, seems to be almost exactly 
counterbalanced by its secretion in the tissues of animals and plants. 

The separation of sodium sulphate, potassium chloride, and common 
salt from the mother liquor derived from the concentration of sea water, 
b}' alternate evaporation and cooling, is the principle of Balard's well-known 
process so largely used in the south of Europe. In Morel's modification of 
this process a low temperature is obtained artificially. When sea water is 
concentrated until its specific gravity is 1.24 (28°B.) it deposits about four- 
fifths of the common salt it originally contained; after adding 10 per cent. 
of fresh water to the mother liquor remaining, it is passed through a refrig- 
erating machine and its temperature lowered to — 18° C. The low tempera- 
ture causes double decomposition to take place between the magnesium 
sulphate and the sodium chloride; sodium sulphate being deposited and the 



184 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

magnesium chloride reaiaining in soIutioD. The mother liquor still retains 
some common salt together with potassium chloride. The first of these is 
obtained by evaporating until the specific gnivity of 1.33 (36°B.) is reached, 
which causes the deposition of nearly all the common salt; the remaining 
liquor is then conducted to shallow vats and allowed to cool; this causes 
the precipitation of the whole of the potassium as the double chloride of 
potassium and magnesium." 

The succession of chemical precipitates formed when sea water is 
evaporated has been succinctly described by M. Dieulafait, in the Popular 
Science Monthly,** from which we quote the following: 

First a verj- wcuk |irccipilatiou »cciim of i^arboDate of Ihnc with a trarc of strontium, luid of 
hydrated seeqaioxide of imn, minKled witli a sliglit pmportiou uf mauganeBe. Tbe water theo cootin- 
iiMtA evapoT&[«, but reiuaiOH periectly limpid, witbtmt foroiiDg any utber <le|ioiiit than the ooe I have 
□leDtioued, titl it has loRt 80 pi>r v«iit. of ila original voluniu. It then begins to kuve an abuDilant 
precipitate of perfi'ctly cryatallizod salphate of lime with twocquivaloTits of water, or gypBDm. iden- 
tival !□ geometrical form itud ehemteal composition with tbat of tho gypniiro-licds. Thia deposit eou- 
tinues until the water han lost S per cent, more of its original volume; theu all precipitation ceasea 
till 2 per oeut. more of tbe original quantity of wal«r han evaporated away. Theu a new deposit 
begiiiB, not of gypBum, bnt of chloride of sodiiiro, or sea-salt. • • • The deposition of pure or com- 
mercial salt continneB till tbe volume of tbe water has been again reduced by one-half, when a precip- 
itation of sulphate of magnesia l)eginH to take ploco with il. This continues, the twoeolta being de- 
posited iu eqnal quantities, till only 3per cent, of tho original quantity of water Is left. Finally, wben 
tbe water baa been concentrated to 'i ]>ercent., carnallite, or the donble chloride ofpolaasinm and mag- 
nesium is deposited. Spontaneous evaporation cannot go much fnrtber. The residual mother-water 
will not dry np at the ordinary temperature even in the hottest regions of the globe ; ita chief constit- 
nent is chloride of magnesiiini. A body of sea-water, evaporated naturally, will then leave a series of 
depositfl in which we will tiiid, as we dig down, the following minerals in order: deliquescent salts, 
inclnding chiefly chloride of magnesiam ; carnallite, or the double chloride of potaBoinm and magne- 
sinm; mixed salts, iiicluding chloride of sodium and sulphate of magnesia-, sea-salt, mixed with sul- 
phate of magnesia; pare sea-salt ; pnregypsnm; weak deposilsof carbonate of lirao with sesquioiiile 

The correspondence between the succession of salts formed by the 
evaporation of sea-water, and the succession found in many saline deposits 
now worked for rock salt, is of great interest, and no doubt explains the 
genesis of some saline deposits. It is not always necessary, however, in 
the explanation of the presence of salts in lenticular basins ta assume that 
the deposits commented with isolated portions of sea-water. On the con- 
trary the study of inclosed basins indicates that deposits of this nature 
sometimes result from the long continued concentration of ordinary river- 
waters. The presence of salt or fresh water mollusks associated with saline 

"Beport of Juries; International Exhibitiou, m6S, Class 11, pp. 48-54. 
■October, 1883. 



SALINE DEPOSITS OP GREAT SALT LAKE. 185 

deposits, in some instances, gives evidence as to whether the beds in which 
they occur were precipitated from ocean or inland waters. 

The precipitation of salts in inclosed lakes is still farther illustrated by 
Great Salt Lake, Utah, the composition of which in the years 1850, 1869, 
and 1873, is given in Table 0. At the present time the lake is lower than 
in 1873, when the last analysis was made, but there is no reason to suppose 
that there has been any change in the salts with which the waters are 
charged. As in all inclosed lakes, the percentage of total salts in a given 
quantity of the brine changes as the waters rise and fall. To illustrate, 
the amount of saline matter contributed to Great Salt Lake during a single 
year, for example, is so small in comparison with the quantity which the lake 
holds in solution, and varies so little from year to year, thatthe composition of 
the residue obtained by evaporating a sample of tlie lake brine would 
remain practically constant for a long period, provided precipitation did not 
take place. The amount of water reaching the lake varies with the seasons, 
and also undergoes secular fluctuations, dependent on climatic changes, 
extending over a term of years. 1^he brine is thus diluted when the lake 
is unusually full, and greatly concentrated when the lake is reduced abnor- 
mally by evaporation. 

Owing to the large amount of sodium sulphate dissolved in the waters 
of Great Salt Lake, and since it is much more soluble in warm than in 
cold water, its precipitation takes place during cold weather. When the 
temperature rises it is redissolved. If the waters of the lake are cooled 
artificially to about 20° Fahrenheit, an abundant precipitation of floc- 
culent sodium sulphate takes place. Each year, on the approach of cold 
weather, the waters of the lake lose their transparency and become cloudy 
and opalescent, owing to the precipitation of sodium sulphate in a state of 
minute subdivision. In the depth of winter the temperature of the atmos- 
pliere about the lake sometimes falls as low as — 20° F. On these occasions 
sodium sulphate is precipitated in immense quantities and collects along the 
shores in thousands of tons. Nature has here anticipated Balard's process 
for obtaining sodium sulphate, and is carrying on the operation on a grand 
scale. 



186 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

From the analyses of the tributary streams we know that large quan- 
tities of calcium carbonate are contributed to Great Salt Lake in solution j 
but the chemist fails to find this salt in the brine itself The extreme 
scarcity of animal and plant life in the waters shows that it could not be 
removed by organic agencies ; it must, therefore, either be precipitated or 
perhaps in part decomposed and changed to the chloride. The very sniall per- 
centage of calcium in the lake, however, is sufficient proof that this element 
must have been precipitated, probably as the carbonate, when the river and 
lake waters were mingled The presence of large quantities of oolitic sand 
along the shores of the lake, which is apparently still in process of forma- 
tion, is strong evidence in support of this hypothesis. This lake furnishes 
a typical instance of the concentration of ordinary meteoric waters by evap- 
oration. We may conclude, therefore, from this and other instances which 
might be enumerated, that in inclosed lakes, as in the ocean, calcium car- 
bonate will be the first salt precipitated as evaporation progresses. 

Great Salt Lake is now so concentrated that the crystallization of com- 
mon salt is taking place in certain portions where the water is shallow. 
Over hundreds of acres along its southwest border the bottom is covered 
with a continuous crust of salt crystals, forming a pavement sufficiently 
strong to support a horse and rider. This condition was observed during 
the arid season ; whether the salt is redissolved during the rainy season or 
not, has not been determined. From the observations recorded above we 
leara that precipitation is now taking place in three separate ways in the 
waters of a single lake ; (a) calcium carbonate is thrown down, probably 
throughout the year, as the tributary streams mingle with the brine of the 
lake ; (6) sodium sulphate is precipitated in all portions of the lake when 
its temperature falls below 20° F.; (c) sodium chloride crystallizes in the 
very shallow portions during the arid season. An example of this nature 
teaches that a stratified saline deposit might form in an inclosed basin as a 
result of fractional crystallization dependent upon changes of temperature. 
The deposits found in the smaller of the Soda Lakes at Ragtown, Nevada 
(see page 79), apparently illustrate such an occurrence. 



CONDITIONS UNDER WHICH TUFA IS DEPOSITED. 187 



DEPOSITION OF CAIiCIUM CARBONATE. 

In considering the natural methods by which calcium carbonate is pre- 
cipitated from solution, we have, as preliminary data, that this salt is more 
abundant than any other in ordinary surface waters, constituting, usually, 
nearly one-half of the total of solids in solution in average rivers ; that it 
is the first to be precipitated when such waters are evaporated ; and that 
calcium ordinarily exists in solution as the bicarbonate, CaO CO2, the pres- 
■ence of free carbon dioxide (^carbonic acid) being essential for its solution. 

Under the conditions prevalent in nature it is evident, from the elemen- 
tary laws of chemistry, that the precipitation of calcium carbonate may 
take place in at least three ways : (a) By evaporation, concentration being 
carried beyond the point of saturation, (b) By the loss of the carbon diox- 
ide necessary to hold the salt in solution. This gas escapes when pressure 
is removed or temperature increased ; it passes off gradually when carbon- 
ated waters are exposed to the air, especially if agitated, as in the spray of 
water-falls and in breaking waves, (c) By chemical reaction, as when an 
alkaline carbonate is added to water holding calcium chloride in solution. 
Of these three methods we need to consider at this time only the results of 
concentration and loss of carbon dioxide ; as dissolved gases are driven off 
during evaporation, these two methods act together. So far as the chem- 
istry of inclosed lakes is concerned it is evident that the precipitation of 
calcium carbonate must depend almost entirely on concentration by evapo- 
ration ; chemical reaction may in certain cases play an important part, as 
when a spring holding CaO COo rises in an alkaline lake; but, in general, 
the conditions under which a number of salts may exist in a solution is too 
little known to warrant one in ascribing a reaction to this cause when it may 
be more simply explained as a result of evaporation. 

With this elementary sketch of the chemistry of natural waters we will 
proceed with our study of the history of Lake Lahontan. 



I * 



:'i = .r 



.. • • . ■ ■ •» 



THEORETICAL SUCCESSION IN SALINE DEPOSITS. 189 

for a long period, or if evaporation were to exceed supply, we should 
expect that other salts would be deposited in a definite succession. The 
probable composition of the waters of Lake Lahontan, if a single evapora- 
tion is considered, indicates that, as concentration took place, the dissolved 
salts would bi», deposited, with some intermixture it is true, but mainly in the 
following order: (1) Calcium carbonate; (2) calcium sulphate; (3) sodium 
sulphate; (4) sodium carbonate; (5) sodium chloride, followed by the precipi- 
tation of the more deliquescent salts In nature, however, this order would 
be altered by fluctuations of temperature, variations in density, and other 
disturbing conditions. Should the desiccation be incomplete the remaining 
waters would form a dense mother-liquor, rich in magnesia, potash, and 
soda, and containing some of the less common substances, as lithium, bo- 
racic acid, etc. 

On entering the Lahonta.n basin — which, as we know, never over- 
flowed — with this theoretical history before us, we are surprised to find 
that, with the exception of immense deposits of calcium carbonate, there 
are no accumulations of saline precipitates to be seen. Moreover, the 
water-bodies now occupying the lowest depressions in the bed of the 
former lake, are not dense mother-liquors, but, on the contrary, contain 
even less than half of one per cent, of total solids in solution. It is evi- 
dent, therefore, that the history we are endeavoring to trace is an excep- 
tion to the rule sketched above, which seemed self evident when considered 
in a theoretical way. As we proceed we hope to explain this apparent 
anomaly, at least in part. 

CALOAKEOUS TUFA. 

The deposits of calcium carbonate occumng in the Lahontan basin 
are most abundant in the valleys where the former lake was deepest, and 
are usually inconspicuous or, perhaps, entirely wanting in places where the 
waters were shallow. The best localities for the study of these chemically 
formed rocks are on the borders of the Carson Desert and about the shores 
of Pyramid and Winnemucca lakes. The steep rocky sides of these secon- 
dary basins, and the isolated buttes occurring in them, seem to have been 



190 GEOLOGICAL HISTORY OF LAKE LAHONTAN 

especially favorable for the deposition and preservation of calcareous de- 
posits. The tufa frequently forms a sheathing 50 or 60 feet thick upon the 
older rocks; at other times it assumes the form of domes and castellated 
masses that in some cases rise a hundred feet above the nuclei about 
which crystallization first took place. Of all such localities in the basin 
the most remarkable are the Marble Buttes at the southern, and the Nee- 
dles at the northern end of Pyramid Lake; Anaho and Pyramid islands 
are also loaded with immense accumulations of tufa, and are points of spe- 
cial attraction to the student of chemical geology. 

Early in the examination of these deposits it was found that they occur 
in definite layers, and form a well-defined sequence in which three main 
divisions, together with many minor variations, may be easily traced 
Classifying the major divisions according to the structure of the rock, begin- 
ning with the first formed, we have: (1) Lithoid tufa; (2) Thinolitic tufa; 
(3) Dendritic tufa. 

LITHOID TUFA. 

We have applied this name to the first of the three main deposits of 
calcium carbonate precipitated from the waters of Lake Lahontan. It is 
compact and stony in structure, light yellowish gray in color, and weathers 
into forms of extreme ruggedness. It frequently shows a concentric and 
sometimes a well-marked tubular structure when seen in cross-section, but 
wlien forming a coating to rock surfaces it is usually composed of thin, 
superimposed layers. In well-exposed sections of lithoid tufa the banded 
structure of the deposit is often distinctly marked, and at times, particularly 
near the base of the deposit, or near the center of the dome-shaped masses 
occuiTing in isolated positions, the layers of tufa having a compact stony 
structure are separated by others of dendritic tufa, the character of. which 
will be described a few pages farther on. Viewed externally, the coatings 
of this variety of tufa on cliffs and buttes appear to be formed of comb-like 
masses, imbricated in such a manner as to resemble a massive thatch. This 
appearance can only be seen to advantage above the limit of the more 
recent tufas; it is especially well displayed on the upper portions of Anaho 
Island and the Marble Buttes. Much of the gravel forming the j)relacustral 
alluvial slopes of the Lahontan basin, as well as that composing the earlier- 



LITHOID TUFA. 191 

formed terraces and embankments, is cemented by it into a compact con- 
glomerate. 

Litlioid tufa is found nearly everywiiere throughout the valleys for- 
merly- occupied by Lake Laliontau, where the conditions for its deposition 
and preservation were favonible. In vertical range it occura from the lowest 
part of the basin now open to inspection, up to a horizon about thirty feet 
below the highest of the ancient beaclies. The broad wave-cut shelf, which, 
so far as can be determined, is the upper limit of this variety, we have called 
the Litlioid terrace (see pagelOl). At its upper limit this tufa is seldom niore 
than eight or ten inches in thickness, as it remains to-day ufteva long period 
of weathering; but lower in the basin it attains a thickness of ten or twelve 
feet; what its maxinumi development may be is difficult to determine, as its 
base is nearly always concealed by lacustral de])nsits or later formed tufas. 

The surface of the litlioid tufa when exposed by the removal of the 
sheathing of thinolite crystals that usually covers it below the horizon of 




Fia. 17.— Section ahawing c II trrnt-beddEil sriTeU bctwwn lltbolrt lud tliluallielnfk 

the thinolite terrace, sometimes shows the effect of weatiiering which took 
place previous to the deposition of the second formed variety. In places 
the two layers are separated by a deposit of pebbles two or ihree feet in 
thickness, united by a calcareous reineuf, or by current -bedded gravels, as 
shown in the following drawing of a section e.\i»osed at tlie ea.steni base of 
the Marble Buttes. In some instances stones and pebbles were carried 



192 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

upwards by the action of sub-lacustral springs about which tufa was being 
deposited, and became inclosed in the calcium carbonate as it was precipi- 
tated; this occurrence is not to be mistaken, however, for the partings of 
current-bedded gravel described above, which must have been deposited by 
waves and currents in shallow water. The weathering of the lithoid tufa 
is not always apparent, but has been observed in a number of instances, 
and can only be interpreted on the suppostion that the first-formed tufa was 
exposed to subaerial erosion by a lowering of the lake previous to the depo- 
sition of the thinolite crystals. The surface of the lithoid tufa above the 
upper limit of thinolite is weathered to a much greater extent than below 
that horizon, indicating that its erosion continued throughout the low-water 
stage during which thinolite was forming. 

The lithoid tufa of the Lahontan basin is identical in structure and 
general appearance with the greater part of the tufa deposited in Lake 
Bonneville, and has essentially the same chemical composition. It is also 
represented on a limited scale in a number of the minor Quaternary lake 
basins of Utah and Nevada. Similar deposits are now forming in Pyramid, 
Walker, and Winnemucca lakes, as described in Chapter III. It is evident 
that this variety of tufa corresponds in all respects with the first calcareous 
deposit precipitated when ordinary meteoric waters are evaporated. 

THINOLITIC TUFA. 

Succeeding the lithoid tufa in order of deposition, and forming another 
coating on the sides of the Lahontan basin, is a deposit of interlaced crystals 
of calcium carbonate, which were called "Thinolite'* by Mr. King.** In the 
reports of the U. S. Geological Exploration of the Fortieth Parallel, however, 
this term is used to designate any of the calcareous deposits of the ancient 
lake, whether crystallized or not. In the present report we restrict the name 
to the variety of tufa exhibiting a definite crystalline structure, presently 
to be described. We may remark, in passing, that no crystals having a 
resemblance to thinolite have been found in the Bonneville basin; nearly all 
the calcium carbonate there deposited is of the character of lithoid tufa, as 

^ U. S. Qeological Exploration of the Fortieth Parallel. Washiagtou, 1878, Vol. I, p. 517. 



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THraOLITIC TUFA. 193 

stated in the preceding paragraph. In a few instances, however, a dendritic 
structure maybe detected; as is the case, also, in the lithoid deposits of the 
lake we are now studying. 

In the Lahontan basin thinolite crystals are only found in the lowest 
depressions, as, for example, about the shores of Pyramid and Winnemucca 
lakes and on the borders of the Carson Desert. Its geographical extent, 
as shown on the accompanying map, embraces the Carson Desert, the val- 
leys of Pyramid and Winnemucca lakes, together with the Black Rock and 
Smoke Creek deserts. The divide between Carson Desert and the valley 
in which Pyramid Lake is situated, is higher than the upper limit of the 
thinolite tufa; we must conclude, therefore, that when Lake Lahontan 
evaporated away sufficiently to admit of the formation of thinolite — or of 
the crystals after which it is a pseudomorph — the water-surface was below 
the level of the pass to the eastward of Wadsworth, and the lake conse- 
quently, divided into at least two water-bodies. On the preliminary map 
of Lake Lahontan, published by the writer in the Third Annual Report of 
the U. S. Geological Survey, the lake at its thinolite stage is represented as 
extending through from the Carson Desert to Pyramid Lake ; this error has 
been corrected on the accompanying map. It was also indicated on the 
previous map, that Smoke Creek and Black Rock deserts were without 
thinolite deposits; later observations have shown that they do occur in 
large masses at certain localities on the borders of these basins, with the 
same general relations to the other tufa deposits that they have in the 
most typical localities. 

The valley of Walker Lake must also have formed an independent 
water-body during the thinolite stage of Lake Lahontan, but no crystals 
belonging to this period of the lake's history have been found in that basin. 
As will be described later, there are masses of thinolite about Walker Lake 
corresponding to quite recent deposits of the same mineral in the Black 
Rock Desert. 

In its vertical range the thinolite is limited by the broad shelf, named 
the thinolite terrace, which occurs at an elevation of 110 feet above the 
1882 level of Pyramid Lake. In only a single instance has the thinolite 
been observed to extend above this horizon. On Anaho Island the terrace 

MoN. XI 13 



194 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

is strongly carved and forms a conspicuous feature in the contour of the- 
island when seen from a distance; on the northern side of the island the 
thinolite tufa extends about 15 feet above the water-Hne of the terrace 
and forms a thin wedge of interlaced crystals included between the lithoid 
tufa and the heavy deposit of dendritic tufa. The upper limit of the thin- 
olite probably varies in the several basins in which it occurs, but no accu- 
rate measurements of diflterences of level have been made. 

The sheathing of thinolite extends from the lithoid terrace down to the^ 
lowest point in the bottom of the basin now open to inspection. Near it&^ 
upper limit it is from 6 to 8 feet thick, but increases to 10 or 12 feet near 
the surface of Pyramid Lake. Like the lithoid tufa it was deposited in 
successive layers, as is shown by its banded structure. Throughout the 
mass we find definite layers or zones of small and large crystals alternating^ 
with each other. Near its outer limit the bands of crystals are divided by 
narrow layers of sheets of dendritic tufa; indicating that the condition of 
crystallization were alternately favorable for the production of the crystal- 
line or the dendritic structure. The circumstances favorable for the for- 
mation of the latter finally prevailed, and only dendritic tufa was deposited* 

PROFESSOR DANa's CRYSTALLOGRAPHIC STUDY OP THINOLITE. 

While carrying on the field study of Lake Lahontan, large quantities 
of the dififerent varieties of tufa were collected, and special attention given 
to securing as many specimens as could well be desired for illustrating the 
structure and mode of occurrence of thinolite. A representative portion 
of this collection, together with similar material from the Mono Lake 
basin, was placed in the hands of Profs. G. J. Brush and E. S. Dana for 
the purpose of obtaining an authoritative statement of the mineralogical 
relations of thinolite. This study was finally undertaken by Professor Dana, 
whose report forms Bulletin No. 12 of the publications of this Survey. To 
the student of Lahontan history this report is especially welcome as it clears 
away the previous hypothesis, advanced by King, to the eff*ect that thino- 
lite is a pseudomorph after gaylussite. The following description of thin- 
olite is quoted with slight verbal alterations from Professor Dana's buUe- 




■ECIMEN OF THIMOLITE, 



THDTOLITIO TUFA. 195 

tin^ to which the reader should refer for a more complete elucidation of 
the subject. 

In general it may be said that the thinolite collected from diflferent 
localities, both in the basin of Lake Lahontan and of Mono Lake, while 
varying widely in external aspect, is yet remarkably uniform in all essen- 
tial characters. It is thus established beyond question that the original 
mineral deposited was throughout the same, although, in consequence of 
the varied conditions to which it has been subjected, the forms resulting 
from its alteration are very diverse. Thus, in some specimens there is only 
a delicate skeleton remaining, the whole consisting of thin plates, held to- 
gther in their parallel position by a slight central frame-work, while in 
others the whole is as firm and compact as a crystalline limestone, and be- 
tween the two extremes many interesting varieties occur. The most impor- 
tant condition upon which this difi*erence depends is the varying extent to 
which a deposition of calcium carbonate has taken place subsequent to the 
first alteration of the original mineral. 

As has already been stated, the thinolite is most characteristically de- 
veloped about Pyramid Lake. The writer has had in hand specimens from 
the Marble Buttes, from the Needles, from Anaho Island, and from the 
Domes, and, as they illustrate well the different varieties, it will be conven- 
ient to refer to them by localities, although no special significance is prob- 
ably to be attached to the particular spot from which the individual speci- 
mens were collected. 

The delicate, open, porous variety of thinolite is best shown in the 
specimens from the Marble Buttes, of which illustrations are given in 
Plates XXXII and in Fig. 1 of Plate XXXIII. The external fonn of the 
crystals is roughly that of a rectangular prism, with projecting edges and 
generally tapering toward the extremities. The color is gray to brown. 
These crystals are commonly from a quarter of an inch to an inch in diam- 
eter and up to 8 or 10 inches or more in length. They are generally 
grouped in a more or less closely parallel position, often Compactly, with 
only very little interlacing. In other cases, especially when the forms are 

^Page 15, ot seq. — ^The o ambers referring to Plates in this quotation have been changed so as to 
denote their position in the present volome. 



I 

I" 



196 GEOLOGICAL HISTORY OF LAKE LAHOKTAN. 

smaller, they have widely divergent positions, interpenetrating each other, 
and giving a large mass an open, reticulated appearance. In addition to 
the elongated crystals, numerous smaller ones, half an inch or an inch in 
length, make up parts of these masses, projecting from the sides of the 
larger crystals and forming divergent groups among themselves. The small 
crystals have generally the form of an acute pyramid, and are sometimes 
square in outline, sometimes rhombic ; the sides are usually concave, and 
the edges project sharply. The exterior surface of the larger crystals is 
rough and open, often with a delicate mossy covering, and the whole crj^stal 
is porous throughout, as if eaten out so as to leave only a skeleton behind. 
Upon a superficial examination no regularity in the structure is evident, but 
on looking more closely it is seen that the apparently rough and irregular 
surface is made up of portions of thin plates, each set parallel to the sides 
of the crystal and uniformly converging in one direction. Thus when one 
of the groups of nearly parallel crystals is viewed end on, from one ex- 
tremity or the other, it is seen that the edges of the plates, irregular as they 
are in outline, are all presented to view at once, as if each crystal, though 
prismatic in general outline, were made up of a series of acute skeleton 
pyramids, hopper-like in form, placed one within another. Still further, 
when the section produced by the cross-fracture of one of these elongated 
crystals is examined, there is seen, more or less distinctly, a series of appa- 
rently rectangular ribs forming concentric squares or rectangles, with diag- 
onal ribs joining the opposite angles. 

The specimens in hand from the Needles, Pyramid Lake, correspond 
closely with those which have been described, though hardly showing the 
structure so clearly. This is also true of some of those from Anaho Island. 
The majority from the latter locality, however, are much more firm and 
compact. Here, too, the crystals are usually elongated, and in a single 
specimen grouped in nearly parallel position. The edges of the plates are 
also commonly distinct on the sides, and show the same convergence toward 
one extremity. The masses, however, instead of being open and porous, 
and consequently light in the hand, are close, compact, and heavy. Instead 
of the delicate, open skeleton, with fretted surface, seen in the cross-fracture, 
the section is nearly solid, and sparkles with the reflection from the cleavage 



Explanation of Plate XXXIIL 

Fig. 1. Group of thinolite crystals from Marble BnttoH, Pyramid Lake (reduced oiio-lialf); opeu porous 

variety. 

Figs. 2 and 3. TrauHverae sectionn, natural size ; Fig. *2, opeu skeleton form ; Fig. 3, partially filled up 
with amorphous CaCOa. Tliesp sections show the system of rectangular (sipiare) and diagonal 
ribs, which consist of granular crystalline CaCOa. 
Fig. 4. External ai»pearaiice (reduced one half) c»f a single crystal, with part of a second, the internal 
structure of which shows that it has but a single termination; the comparatively smooth surface 
» is due to the secondary deposition of CaCOa, 
Fig. 5. Longitudinal section of open vaiiety (reduced one-hnlf), showing the two systems of plates 

converging upward at an angle of about '.i^^. 
Fig. 6. Complete; crystal (reduced one-half) which yielded the section in PMg. 2; the line in which the 

section was made is indicated. 
Fig. 7. Acute pyramidal cr;^stal (reduced one-halt) which yielded at its base the section given in Fig. 3. 
j Fig. h. Si^uare pyramidal crystal (reduced one-half) which gave, at the point indic:it.ed, the section in 

i Fig. 13 ; the surface has been made smooth by subse<iueut <leposition of CaCOs. 

j Figs. 9 and 10. Skeleton crystals (natural size) showing cap-in-caj> structure, ai.d thus revealing the 

i true square pyramidal form of the original mineral. 

I Fig. 11. Crystals (natural size) from the Domes, Pyramid Lake; the surface smootho*! over by subse- 

quent depositions of CaCOa, with sproutings from the edges and extremiii<'s. 
j Fig. 12. Section (magnified 8 times) of a crystal fnmi the Domes, like that in Fig. 11, showing a 

I diagonal and rectangular frame-work, partly crystalline, granulur, partly amorplxMis, with layers 

; of si'condary carbonate opal-like in stnicture. 

! Fig. 13. Section (natural size) of the crystal shown in Fig. 8, cut transversely at point indicatesd; it 

j shows the same frame-work of granular crystalline carbonate, partially tilled in with secon<lary 

4 CaCOrj. 

* Fk;. 14. Section (natural size) showing the usual frame-work, partially filled in withs<^condary CaCOs, 

j and with successive layers also around the outside. 

Fig. 15. Section of acrystal from the Marble Huttes, magnified H times, and showing the structuni lines 

of crystallized carbonate, and also in the cavitie.^ tlie acicular crystals (»f aragonite. (f) 
Figs. Ifi and 17. Small pyramidal crystals (natural size), showing by dissection the cap-in-cap struc- 
ture, and thus, like Figs. 9 and 10. revealing the true [tyramidal form of the original mineral. 




.I.USTHATIOMS OF THE ST^UCTIJ«E ' 



/ 



THINOLITIO TUFA. 197 

sarfaces of the calcite grains. In other cases the outer surfaces are smooth 
and rounded, and the unaided eye sees little of the structure except on a 
cross-fracture ; in these instances, as will be more fully explained immedi- 
ately, a deposition of calcium carbonate has. filled up the skeleton form and 
incrusted and smoothed over the surface. 

The specimens from the Domes represent still another type of the 
tuinolyte. The crystals here have uniformly an acute pyramidal form, and 
are grouped in irregular, divergent positions. Their surfaces are brownish 
J ellow in color and show little of the edges of the parallel plates conspic- 
uous in the variety from the Marble Buttes They are, on the contrary, 
nearly smooth, except when covered with watery excrescences, which in 
some cases are thickly clustered about the edges and extremities. One of 
these crystals (natural size) is shown in Fig. 11, PI. XXXIII. On the fracture 
this variety is found to be nearly as firm and compact as a fine-grained crys- 
talline limestone ; in fact, the unaided eye would regard the whole as crys- 
talline throughout. The color on tlie fracture is slightly yellowish white. 

Examination of sections of crystals, — In order to get at the true structure 
of the crystals which have been described, it is necessary to resort to sec- 
tions cut transversely and longitudinally ; these reveal the form most clearly 
and satisfactorily. A cross-section of a crystal like those first described — 
the open, porous variety from Marble Buttes — is shown in Fig. 2 (natural 
size). As seen in the figure it is made up of lines in position parallel to the 
sides of a square prism, and in addition there are two sets of distinct diago- 
nal lines intersecting at right angles to each other ; between these ribs are 
open spaces. A closer examination of the specimen represented in Fig. 2 
shows that the material consists of rhombohedral calcium carbonate, or cal- 
cite, of a distinctly granular crystalline structure throughout. The whole 
presents an open tessellated appearance. The external form of the crystal 
which yielded Fig. 2 is shown reduced one-half in Fig. 6. The point at 
which it was divided is indicated by a black line. The form is roughly that 
of a square prism tapering slightly in both directions, but the external form 
does not conform, in this respect, to the internal structure except at the 
upper extremity. The irregular edges of the upwardly converging plates 
are clearly shown in this figure. 



198 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

A longitudinal section of another crystal (one-half natural size) is 
shown in Fig. 5. It presents also an open skeleton appearance analogous 
to that of Fig. 2. As seen in the figure the plates converge upwards on 
either side of the longitudinal, axis, meeting at an angle of approximately 
35°. Like the previous case, it consists entirely of purely granular crj^s- 
talKzed calcite with only a little mossy covering on the surfaces of the 
plates. It is to be noticed here that the plates all converge upwards from 
one extremity of the crystal to the other, and this, as will be remarked 
later, is almost universally true even in the case of crystals, the external 
form of which tapers oflF at both ends. 

Another transverse section (natural size) is shown in Fig 3. It is 
like Fig. 2 in most respects, except that the square is elongated in one 
direction and the diagonals meet in a central rib. Moreover while the 
skeleton frame-work consists as before of crystallized calcite (left white in 
the drawing), the intermediate spaces are partially filled up with a secon- 
dary deposit of calcium carbonate, which is apparently amorphous, and 
has been deposited in granular form and, too, in lines parallel to the 
crystalline plates. This subsequent deposition, however, has not gone far, 
and the general appearance is nearly as open as the one first described. 
The outline of the crystal which yielded this section is shown in Fig. 7 
(reduced one-half). As seen here it tapers gradually to the terminal edge, 
forming a sharp extremity. The external form approximates to the true 
crystalline form of the original crystal, but is somewhat more acute, as 
shown by the edges of the plates exposed on the surfaces, and by the angle 
at which the plates within converge. 

In Fig 13 another section is given (natural size). This shows much 
the same tessellated appearance, the structure being essentially the same as 
in the others described, but the secondary deposition of amoiphous calcium 
carbonate has gone still further, so that as a whole it is more compact. 
The skeleton ribs parallel to the sides and the diagonals are, however, 
still very distinct and entirely crystalline. The form of the crj'stal which 
gave this section is shown in Fig. 8 (one-half natural size). As seen here 
it is an acute square pyramid, approximately conforming in outward form 
to the internal structure. The surface is here no longer open and fretted, 



I 

1: 

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Explanation of Plate XXXIV. 

Fig. 18. Thinolit^i from Black Rock Desert (reduced one-lialOi the iudividual crystalH mnning off into 
a compact stony tufa, ho lliat the mass from nhove has a caiilitlower-like form. 

Figs. 19 and *20. Thinolite from Mono Lake, California (natural Hiz<^), showing the grouping of the 
composite crystals. 

Fig. 21. Thinolite from Mono I^ake (natural size), fragment of a large composite crystal, made np of 
small acicular crystals in parallel position. 

Fig. 22. Transverse section c»f the crystal repres<*nted in Fig. 21, showing the same skelet'On strnctnre 
distinct in crystals fnmi Pyramid Lake (Figs. 2, X etc.). 

Figs. 23 and 24. Gronp of thinolite crystals from Mono Lake (natural size), showing the acicular form, 
and also the? way in whi<'h the crystals are coated over with secondary carhonate. 

Fig. 25. Group of small crystals (magnified 4 times) from Mono Lake, showing the same method of 
grouping common in the Sangerhausen pseudomorphs, as shown in Fig. 26. 

Fig. 26. Group of Sangerhausen pseudomor]dis (natural size) ; compare Fig. 25. 

Figs. 27 and 28. Isolated thinolite crystals (magnified twic»^), showing resemhlance in form and sur- 
face marking to Sangerhausen crystals ; compare Figs. 31 and 32. 

Fig. 29. Thinolite crystal (natural size), showing cap-iu-cap pyramidal structure, similar to Figs. IG 
and 17, Plate 11. 

Fig. 30. Thinolite crystal (magnified 4 times), showing resemhlance in form to the Sangerhausen 
pseudomorphs ; compare with Figs. 31, 32, and 38. 

Figs. 31 and 32. Single Sangerhausen crystals, showing form and external markings; Fig. 31, natural 
size ; Fig. 32, magnified twice. 

Fig. 33. Group of small thinolite crystals (nicignified 4 times); compare with Fig. 2<). 

Figs. 'M and 35. Pseudomor])hous crystcals, consisting of granular calcite from Astoria, Oregon ; copied 
(reduced one-halt) from figures hy J. D. Dana in the Geology of U. S. Exploring Expedition, p. <>5(^ 

Figs. 36 and 37. Pseudomorphous crystals, consisting ot granular calcite, fnun New South Wales; 
copied (reduced one-half) from figures hy J. D. Dana in the Geology of the U. S. Exploring Ex- 
pedition, p. 4H1. 

Fig. 38. Pseudomorx)hous crystal (natural size) from Kating, Silesia. 




i: E,THUC1Ui-E ' 



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I I 



THINOLITIO TUFA. 199 

as in the others, but nearly smooth, except as it is covered with small wart- 
like prominences. The color is a dark brown. The line in which the 
section was cut is shown in the figure. 

Still another section is shown in Fig. 14 (natural size), and one 
which marks a further degree of deposition of secondaiy calcium carbonate. 
The crystal from which it was taken had a square form tapering slowly 
upward, and the surface was covered with small mammillary prominences. 
The skeleton of crystalline calcium carbonate is here nearly concealed by 
the added amorphous material, and the outer portion consists of concentric 
layers of the same substance. 

The exterior appearance of another crystal is shown in Fig. 4 (one- 
half of natural size). As seen, it tapers slightly toward both extremities, 
and it was cut longitudinally, in the idea that it might be a doubly ter- 
minated crystal, but the structure lines all converged toward one end, 
showing that, like most of the others, the growth was only in one direction. 
As the surface indicates, the crystalline skeleton has been nearly filled up 
with amorphous calcium carbonate. 

In addition to the sections given and others like them of large crys- 
tals, numerous thin sections were also cut transverse and longitudinal to 
smaller crystals. They revealed under the microscope the same points 
which the microscopic examination of the larger sections showed— that is, 
the presence of the same skeleton of crystallized calcium carbonate vrith 
the concretionary depositions added to it. The calcite grains are large, 
each one having a distinct rounded or elliptical outline, and they are 
packed closely together, with a little brownish amorphous matter between 
them. Many of them show the rhombohedral cleavage; others show a 
crystalline nucleus which has apparently grown by the addition of further 
crystalline matter. The secondary calcium carbonate has generally a 
concentric or banded structure resembling some kinds of opal. 

These sections also show another point of interest; namely, the pres- 
ence of groups of 'acicular crystals in parallel position filling more or less 
completely the cavities in the skeleton structure, and sometimes projecting 
into the cavities. These are seen in many cases, and are the general rule, 
though sometimes absent; they are indicated magnified eight times in Fig. 



200 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

15. These acicular crystals show uniformly extinction parallel to their 
prismatic direction, and hence it seems clear that they must belong to an 
orthometric system. It seems probable that they are aragonite. A chem- 
ical examination of an uncovered slide gave results in accordance with this 
suggestion. 

A section of one of the crystals from the Domes is shown in Fig. 
12 magnified eight times. To the eye the broken crystal appeared to be 
crystalUne throughout; in the section, however, as examined under the 
microscope, there is seen to be a crystalline frame- work made up of calcite 
grains, filled in with amorphous matter, and in addition outer .layers of 
banded opal-like carbonate, so that it conforms in general to cases like 
those before represented. The diagonal lines are here clearly developed, 
and there are also rectangular lines more or less distinctly indicated. 
These are illustrated somewhat obscurely in the figures. Other sections 
showed essentially the same relations. 

Strticture in dissected crystals. — As has been stated, the external form 
of the thinolite crystals seldom gives the true crystalline form. The process 
of dissection, however, which has laid bare the skeleton-like ribs which 
have been described, sometimes results in showing the true pyramidal form 
of the original mineral. In such cases we may have a series of skeleton 
crystals, each a hollow pyramid as a cap to the one preceding. This is 
shown in Fig. 9, which will explain itself, and again in Fig. 10 (both 
natural size). In another case a mass of the calcareous tufa, showing little 
structure, has its surface partially covered with pyramidal crystals an inch 
in length. Each one was a skeleton crystal inclosing a pyramidal crystal, 
and sometimes several crystals after the fashion of a nest of pill-boxes. 
The outer surface of the crystals was incrusted with a moss-like covering, 
often entirely hiding the form. Two of these are represented in Figs. 16 
and 17 (natural size), and another in Fig. 29, Plate XXXIV. 

Before passing to the description of the next succeeding tufa deposit, 
we may note that the external surface of the thinolite does not exhibit 
evidence of having been weathered previous to the deposition of the den- 



DENDRmC TTJFA. 201 

dritic variety. This may be taken as conclusive evidence that the lake 
surface did not fall below the horizon of the thinolite terrace subsequent to 
the deposition of thinolite until after the dendritic tufa was formed. 

DENDRITIC TUFA. 

A change in the chemical nature of Lake Lahontan, which terminated 
the crystallization of thinolite, is recorded by a third calcareous deposit, 
which, from its resemblance in structure to arborescent forms, we have 
called dendritic tufa. The conditions that brought about this change in the 
character of the calcium carbonate precipitated appears to have been a 
dilution of the waters in which the thinolite was deposited. This is evident 
from the fact that the dendritic tufa reaches a higher level than the layer of 
thinolite. This third variety is by far the most abundant of all the chemi- 
cal deposits of Lake Lahontan, and occurs from the bottom of the basin up 
to an elevation of 320 feet above the level of Pyramid Lake in 1882. In 
many places it is not less than 50 or 60 feet in thickness and may at times 
exceed this amount. The principal precipitation took place at an elevation 
of between 200 and 300 feet above Pyramid Lake. The abundance of the 
accumulation at this horizon is so great that it gives a convex outline to the 
cliflfs on which it was deposited, as may be seen at the Marble Buttes and 
on the islands in Pyramid Lake. It is frequently suspended from cliflfs in 
pendent, comb-like masses, which sometimes suggest the appearance of 
Cyclopean tile-work, and present surfaces of extreme ruggedness. The 
aspect of cliflfs when loaded down with tufa is well shown on Plate XXIV, 
Vol. I, of the reports of the United States Geological Exploration of the 
Fortieth Parallel, and is also represented on Plate XXXVI of the present 
volume. Like the lithoid and thinolitic tufas already described, the den- 
dritic variety is yellowish gray in color and weathers into similar rough 
and angular forms. It is distinguishable at a glance, however, from the 
earlier varieties by its peculiar dendritic structure. In typical specimens, 
the sprays of tufa branch and expand from central nuclei, in such a manner 
as to appear not unlike twigs of cedar changed to stone. This arborescent 
or dendritic structure is shown on Plate XXXV, which is a reproduction of 



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i 



jl. 



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ANALYSES OF TUFAS. 



203 



clays. The occurrence of evenly stratified lacustral beds, containing the 
shells of fresh- water moUusks, above the layer of dendritic tufa, is evidence 
that the lake rose after the precipitation of the tufa and was essentially 
fresh. 

As in the earlier formed varieties, a section of the sheathing of dendritic 
tufa exhibits many alternating bands, showing that the deposition took 
place from without and was subject to many variations. 



CHEMICAL C031P0SITI0N OF THE TUFA DEPOSITS. 

Carefully collected samples of each of the varieties of tufa described 
above were submitted to Prof. 0. D. Allen, of Yale College, for analysis, 
who reports their composition as follows : 



Conatitaents. 

Insoluble residue 

Lime (CaO) 

Magnesia (MgO) 

Oside of iron and alumina . 

Carbonic acid (COs) 

Water (IIsO) 

Phosphoric acid (POs) 

Chlorine and sulphuric acid 

Total 



Lithoid tufa. 


Thinolitic 
tufa. 


Dendritic 
tufa. 


1.70 


3.88 


5.06 


50.48 


50.45 


40.14 


2.88 


1.37 


1.99 


.25 


.71 


1.29 


41.85 


40.90 


40.31 


2.07 


1.50 


2.01 


.30 


trace. 


trace. 


trace. 


trace. 


trace. 



99.53 



98.81 



99.80 



It will be seen from this report that the composition of the tufas gives 
no hint as to differences in the conditions under which they were deposited. 
With the exception of the insoluble residue, which may be considered in a 
measure as accidental — being in part foreign matter imprisoned during the 
precipitation of the tufa, and in part carried into the insterstices of the rock 
as atmospheric dust after the desiccation of the basin — the various specimens 
have essentially the same composition. Special tests have been made in 
the case of thinolite to determine if in some instances it might not contain 
notable quantities of calcium chloride or other similar salt, but the results 
were negative. In common with all the tufa deposited in the Quaternary 
lake basins of the Far West, the several Lahontan varieties, as found at the 
present day, are simply impure calcium carbonate. 



204 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



SUCCESSION OF TUFA DEPOSITS. 



The relation of the three varieties of tufa to each other, and the man- 
ner of their occun-ence on the interior of the Lahoiitan hasin, are indica- 
ted in the following ideal section of the lake shore: 




Fia. 26.— DUigram sboviog BDCceuioa of lufB dcposlta. 

The first formed deposit, lithoid tufa, extends upward ahout 500 feet 
above the horizontal lake-beds occupying the bottom of the basin. The 
second deposit, thinolitic tufa, finds its upper limit about 100 feet above the 
present level of Pyramid Lake. The third and last, dendritic tufa, extends 
upwards to within approximately 200 feet of the highest shore-line. The 
lower limits of the tufas cannot be determined with accuracy, as they are 
concealed by lacustral sediments. 

Considering these deposits by themselves, we learn that Lake Lahon- 
tan rose to about the level of the lithoid terrace, and then evaporated away 
to a horizon certainly somewhat lower than the present level of Pyramid 
Lake. During this evaporation the lithoid tufa was deposited, and evi- 
dently owes its precipitation directly to the concentration of the lake waters. 
The lake was then refilled to the level of the thinolite terrace, where it 
must have maintained a nearly constant horizon for a long time. Concen- 
tration by evaporation continued and the deposition of the crystals after 
which thinolite is a pseudomorph, took place. From this horizon the lake 
surface was carried upwards about 220 feet, with many oscillations, and 
for a long period deposited dendritic tufa. Subsequently the basin was 
more completely filled, as is shown by the lacustral beds that occur above 



■-?swi-- 




.5 ;...'•'.' 



SUCCESSION OF TUFA DEPOSITS. 205 

the dendritic tufa in the Humboldt and Truckee cafions. During this last 
rise the water surface reached a horizon about 30 feet above the lithoid 
terrace, and carved the Lahontan beach — the highest water-line in the 
basin. * From this level the lake evaporated away until the basin reached 
at least its present condition, and probably a much greater degree of des- 
iccation. We should expect that other deposits of tufa would have been 
formed during this final evaporation. Thus far, however, there are but few 
observations to sustain this hypothesis. Smoke Creek Desert and the val- 
ley of Pyramid Lake are separated by a low divide, which at a certain 
stage in the lowering of the lake must have parted the waters inithe two 
valleys. The basin now floored by the desert underwent complete desic- 
cation, and on its surface we find the mineral matter precipitated from the 
waters as they evaporated. The desert where not concealed beneath recent 
playa deposits, is covered with an abundance of thinolite crystals, mostly 
scattered and broken, which, from their position, must have been deposited 
during the last recession of the waters. The highest point at which this 
tufa was found may be taken at about 50 feet above the surface of the 
desert, or a little below the level of the divide at the southern end of the 
basin. The crystals scattered over the surface of the desert are somewhat 
diff^erent in appearance from tlie tliinolite found in such abundance about 
Pyramid Lake; and, at their upper limit, pass into a dense, compact, and 
usually botryoidal mass which closely resembles gray stone-ware. See Fig. 
18, Plate XXXIV. As is common with tufa deposits, these crystals are 
usually grouped about solid nuclei, and frequently form rosette-shaped 
masses 4 or 5 inches in diameter. 

Direct superposition of this variety of tufa upon the dendritic has not 
been observed; but the sediments on which it rests are probably of the 
same date as those covering the dendritic tufa in the Truckee and Hum- 
boldt caiions. Tliinolite crystals of the same character as those scattered 
over the surface of the Smoke Creek Desert, have been observed at the 
southern end of Winnemucca Lake, and on the shore of Walker Lake; at 
the time of their formation, each of these basins must have contained an 
independent water-body. 



206 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

In the valley of the Humboldt, near Humboldt Lake, a thin deposit of 
yellowish, coral-like tufa has been observed coating domes of the dendritic 
variety, which is quite different from any of the lower tufas occurring in 
the basin. 

From their position at the top of the series we refer both of the varie- 
ties of tufa described above to the last evaporation of Lake Lahontan. The 
coral-like form was deposited when the lake filled its basin up to within 
80 or 100 feet of the Lahontan beach; and the thinolite was crystallized 
when evaporation had lowered its surface so greatly that it became divided 
into separate basins, one of which, the Smoke Creek Desert, was completely 
desiccated. 

About Pyramid Lake, where the records of Lahontan history are most 
complete, these evidences of the last recession of the waters have not been 
satisfactorily observed. The absence of the second deposit of thinolite in 
this basin is possibly due to the depth of the waters that occupied it, which 
did not reach a sufficient degree of concentration to admit of the formation 
of thinolite crystals, at least not in that portion of the basin now open to- 
inspection. Observation has thus far been unable to show conclusively 
that coral-like tufa similar to that formed at a recent date in the Humboldt 
Valley, occurs at other localities, but an outer coating on many of the 
domes about Pyramid Lake is very similar and is probably of the same 
date. Its general absence may perhaps be accounted for in many locali- 
ties by assuming that it would be the first of the tufas to be removed by 
erosion, after the evaporation of the waters in which it was deposited. Our 
information regarding the later-formed varieties of tufa is but fragmentary, 
and does not afford as complete a record of the post-dendritic oscillations 
of the lake as could be desired. 

Carrying our study of tufa deposits one step nearer the present, we find 
that the rocks and tufa-crags about Pyramid Lake are coated with a thin de- 
posit of calcium carbonate, in the form of compact gray tufa, up to the height 
of about 12 feet above the level of the lake in 1882. This sheathing also de- 
scends beneath the lake surface and, judging from its freshness, it is evident 
that it is still in process of formation. The similarity between the tufa now 
forming and the variety first deposited from the waters of Lake Lahontan^ 



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TUFA DOMES, CASTLES, AND CEAGS. 207 

indicates tliat the coiicentratipn of the waters of Pyramid Lake at present 
must approximate that of tlie ancient lake during its first rise. In sheltered 
bays among the Needles, where springs with a temperature of about 100° F. 
rise in shallow water, there are beaches of creamy- white oolitic sand, which, 
like the calcareous coating on the rocks, is still in process of formation.^ 
The calcium composing the oolitic sand is probably derived. from the warm 
springs near at hand, which are also depositing a light-colored, porous tufa^ 
on the lake bottom. In a number of instances, tubular and mushroom- 
shaped growths occur about the orifices of the submerged springs. Some 
of these in-egular tubes rise 5 or 6 feet above the bottom of the lake, and 
afford passages for the warm waters that stream through them. It is evi- 
dent that the precipitation of calcium carbonate commences at this locality 
at the instant that the warm spring-water comes in contact with the cooler 
and denser water in which it rises. Ko chemical examination of these 
spring waters has been made, but judging from their taste they are prac- 
tically fresh. The tubular forms produced are high in comparison to their 
diameter and form miniature towers and domes, which in deep, still water 
might grow to be of large size. A few of them are represented in Fig. 6, 
page 61. They assist one in understanding the origin of certain Lahon- 
tan tufas, which we shall next consider. 

TUFA DEPOSITS IIS^ THE FORM OF TOWERS, DOMES, CASTIiES, CRAGS^ 

ETC. 

In the foregoing descriptions our attention has been directed to the 
layers of tufa sheathing the interior of the Lahontan basin. We now turn 
to other deposits of the same nature occurring in isolated positions at vari- 
ous distances from the borders of the valleys, which we shall call tufa 
domes, towers, castles, etc., as their forms may suggest. Some of these 
masses are now wholly or in part submerged beneath the waters of the ex- 
isting lakes, wliile others are scattered throughout the desert valleys whicli 
were formerly flooded, and frequently resemble isolated watch-towers or 
crumbling rains, the origin of wliich must be a puzzle to one not familiar 

^The general features of this locality have been noticed in describing Pyramid Lake, page 60. 



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208 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

with the mode of their formation These tufa-forms occur of all sizes, from 
mushroom-shaped cakes a few inches high, up to castellated masses rising 
over a hundred feet above the desert, and frequently contain many thousands 
of tons of calcium carbonate. Isolated tufa-masses may be studied to advan- 
tage about the shores of Pyramid and Winnemucca lakes, and at a few local- 
ities on the bord<ers of the Carson Desert. The rugged promontory known 
as the Needles is surrounded by a number of peculiarly shaped islands 
which rise from 15 or 20 feet of water to a height of 40 or 50 feet above 
the lake's surface. The Needles and all the associated islands are composed 
of tufa, which takes the form of towers and domes of the most rugged and 
picturesque description. The highest of the Needles rises like a cathedral 
spire to the height of 300 feet, and is apparently composed of tufa throughout 
At the top only lithoid tufa is found ; at the base of the spire, where the rock 
swells out and forms a dome, there is a great thickness of the dendritic vari- 
ety ; at the base, where the rock has been weathered and broken, a heavy de- 
posit of thinolite crystals is exposed, interstratified between the lithoid and 
the dendritic. The precipitation of calcium carbonate has been so abundant 
at this locality that the rocky nucleus about which the crystalUzation com- 
menced can only be seen in a few places. 

In some instances tufa domes and towers are grouped in clusters and 
unite with one another in such a manner as to form castle -like masses of 
great size, which call to mind the ruins of mediaeval strongholds. The ap- 
pearance of one of these water-built structures standing on the western 
shore of Pyramid Lake is shown on Plate XL ; like all the tufa deposits 
in the basin that are not submerged, this ancient castle is fast crumbling 
into decay and ruin. 

Isolated towers and shafts of tufa are sometimes seen standing on the 
I desert in independent masses that are frequently 50 or 60 feet high, and 

furnish most instructive examples of deposits of this nature. These struct- 
ures are frequently weathered and broken in such a manner as to expose 
every desirable section of their interiors, and afford abundant opportunity 
for the study of their anatomy. The inspection of some of these broken 
shafts shows at a glance that they have a concentric structure, and are com- 
posed of three varieties of tufa, as in the case of the deposits sheathing the 



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TUFA TOWERS. 209 

interior of t!ie basin. A cross-section of one of these columns is slinwn in 
the foUowinj^ diii^^nvni. The central portion (a) is of compact lithoid tiifit, 
which usually exhibits a concentric or tubular stnictui-e, and is very fre- 
quently from G to 10 feet in diameter; Burronnding this core is a layer <if 
thinolitc crystals, forming- the concentric band {b), which is commonly from 
2 to 6 feet thick ; outside of this layer is a coating of dendritic tufa ((-■), 
of somewhat greater thickness than tho thinolite layer, which sheathes the 
outside of the tower and arches over the low dome forming its summit. 




ot only are these isolated towers composed of distinct layers of the 
three varieties of tufa we have mentioned, but each of these main divisions 
is itself banded. The cross-section of some of the tufa towers shows that 
the inner core of lithoid tufa is composed of as many as fifteen or twenty 
distinct envelopes ; at the center and near the outer marghi, some of these 
hands have a dendritic structure. Sections of the middle or thinolite mem- 
ber reveal that it also is composed of a large number of concentric bands, 
some formed of large, and some of small crystals ; near the outer ])Ortion 
of this deposit thin layers of thinolite alternate with narrow bands of den- 
dritic tufa. Tho outer sheathing of dendritic tufa is also comi>OHed of many 
layers. Kacli of these concentric circles seen in the cross-section of a tufa 
tower, like the annual rings of an exogenous tree, is a section of a cylinder 
that has been formed about the previous one. It is evident that each con- 
centric band records a change of greater or less importance in the character 



210 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

of the solution from wliich the calcium carbonate was crystallized. The 
lithoid and dendritic varieties having a much closer resemblance to each 
other than either has to the middle or thinolite member; it is apparent that 
the chemical conditions which favored their deposition, although not ident- 
ical, were not widely divergent. As the first and tliird members of the 
series were deposited when the lake was deep and of broad extent, we may 
conclude that they were precipitated from comparatively dilute solutions ; 
the thinolite, on the other hand, is only found low in the basin, and must 
consequently have crystallized from waters that were more concentrated 

The structure of the isolated domes, towers, castles, etc., corresponds, 
even in minute detail, with the structure of the tufa layers sheathing the 
sides of the basin ; thus adding strength, if additional evidence were needed, 
to the conclusion that they were deposited during three well-defined stages 
in the history of the former lake. 

CONDITIONS FAVORING THE DEPOSITION OF TUFA. 

From the facts already gathered concerning the history of Lake La- 
hontan, it is evident that the principal condition which favored the precipi- 
tation of the calcium carbonate dissolved in its waters, was concentration 
by evaporation ; the tributary streams at the same time continuing to sup- 
ply fresh quantities of calcium carbonate. We do not forget, however, that 
chemical reactions must have taken place among the various salts as the 
lake became concentrated, which would affect the nature of the precipitates. 
The conditions under which a mixture of saline substances exists in solu- 
tion are too little known, however, to enable one to determine what 
changes may have taken place 

The conditions favoring the formation of lithoid tufa seem simple in 
their nature and not difficult to determine. This variety is apparently iden- 
tical with that precipitated in neighboring Quaternary lakes, and is very 
similar to the deposits now forming about many springs, or being precipitated 
from the spray of water-falls, and from the waters of lakes in which evap- 
oration equals or exceeds supply. The deposits now forming owe their de- 
position to the loss of carbon dioxide, and to evaporation ; and are so sim- 
ilar to the first-formed Lahontan tufa, tliat there seems no doubt but that 



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CONDITIONS UNDER WHICH TUFA WAS DEPOSITED. 211 

the ancient tufa was deposited in a similai- manner and was a direct precip- 
itate from lake waters. It is evidently not a pseudomorph, and since its 
deposition has undergone but slight change. 

We have already noted that the dendritic tufa is much more closely 
related in its structure to the lithoid than it is to the thinolitic vaiiety. The 
alternation of lithoid and dendritic tufa in narrow bands indicates that the 
conditions under which they were deposited were very similar. At the time 
each of these varieties was precipitated the lake was of broader extent and 
had a much greater depth than when the crystallization of the thinolite 
took place. From these facts we conclude that the dendritic tufa, like the 
lithoid, was precipitated when the lake waters were moderately concen- 
trated At the time of its formation, however, they must have been more 
highly charged with chloride of sodium, alkaline carbonates, etc., than 
during the early part of its history. The presence of these salts may ac- 
count for the peculiar forms assumed by the calcium carbonate upon crys- 
tallizing. This variety of tufa, like the lithoid, has remained practically 
unchanged since it was deposited, and cannot be considered a pseudomorph 
after any other mineral. 

From the relative height of the various tufa deposits on the sides of 
the Lahontan basin we know that the lake was much lower during the thi- 
nolitic stage than when the other varieties of tufa were formed. It was, 
therefore, presumably a more concentrated chemical solution. This state- 
ment requires qualification, however, when we consider that between the 
lithoid and thinolitic stages the lake sank far below the thinolitic teiTace and 
may have undergone complete desiccation. If the lake was evaporated to 
dryness at that time, one of three results might have ensued : (a) The pre- 
cipitated salts might have been buried beneath playa deposits, in which case 
the lake formed when the basin was partially refilled might have been essen- 
tially fresh, (b) The lake might have been partially refilled before any of 
the precipitated salts were buried, in which case it would be an alkaline and 
saline solution of the same character as during the low stages previous to 
desiccation, (c) Lastly, a partial precipitation and burial of the saline con- 
tent might have occurred; in this case the less soluble salts would have been 



212 GEOLOGICAL UISTORY OF LAKE LAHONTAN. 

removed, leaving the waters in the condition of a mother-liquor, character- 
ized by the presence of the more deliquescent salts. Let us consider the 
probable effect of each of these conditions on the character of the calcium 
carbonate subsequently deposited. 

If the first case, we should expect that there would be but a slight, 
if any, deposition of tufa in the rising lake. If precipitation of calcium 
carbonate did take place, however, it would be expected to have the same 
characteristics as the tufa formed during the first high-water period, but as 
the thinolite is markedly different from the lithoid tufa we may disregard 
this postulate. 

If the second were true, and all the precipitated salts were rdissolved, 
the previous condition of the lake would be practically re-established, and 
the ensuing deposits of tufa could not be expected to differ from that pre- 
viously precipitated. 

If the third were true, a change in the nature of the lake when the 
basin was partially refilled would result. The first salts to be deposited 
from a brine obtained by the concentration of waters like those found in 
the rivers of the Lahontan basin would be calcium carbonate, calcium sul- 
1 . phate, and sodium chloride. As calcium carbonate had already been depos- 

i I ited in immense quantities, and the per cent, of calcium sulphate was prob- 

ably small, the principal salt that would be precipitated upon a partial 
crvstallization of the substances dissolved in the concentrated lake water 
would be sodium chloride. If the precipitation and burial of the mineral 
substances in solution had been stopped at this stage and the basin partially 
refilled, the resulting lake would have been characterized by the presence 
of more soluble salt» among which the alkaline carbonates would have pre- 
dominated. The calcium carbonate subsequently contributed by streams 
and si)rings as the lake rose would have been precipitated under different 
conditions than had previously obtained, and this might have caused it to 
assume a different crystalline form. Thus the postulate of a partial desic- 
cation of the basin agrees best with the facts observed. 

As a qualification of the second hypothesis, we might assume, that 
during the time intervening between the formation of the lithoid and thino- 
litic tufiis concentration was continued for a long period without the depo- 



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CONDITIONS UNDER WHICH TUFA WAS DEPOSITED. 213 

sition of any of tlie contained salts. The water would thus be more highly 
charged with saline matter when the lake rose to the level of the tliinolite 
terrace than when it previously stood at that horizon. Under these con- 
ditions the composition of total salts would remain practically constant, but 
their percentage in a given quantity of water would be increased. Our 
ignorance of the influence that the presence of various salts exerts on the 
character of the calcium carbonate j)recipitated from saline wg^ters renders 
it impossible for us to predict that it would differ in crystalline form when 
deposited in strong or weak brines. A partial desiccation would cause a 
more marked change in the chemistry of the lake than continued concen- 
tration. We are inclined, therefore, to the belief that the former is the 
more probable hypotliesis of the two. 

The positive element in the i)roblem is that a marked change did take 
place in the character of the calcium carbonate precipitated, which is proof 
of an alteration in the chemistry of the lake waters, unless the question of 
temperature be considered as of weiglit in the problem. The assumption 
that this change was an increase in tlie j)ercentage of alkaline carbonates 
in the waters is strengthened by the fact that tliinolite has only been found 
in this country in basins characterized by the presence of these salts, viz, 
in the Lahontan and Mono basins. In the Bonneville basin, tufa was depos- 
ited on quite an extensive scale, but it did not assume the form of thinolite. 
Since that basin last overflowed its waters have been concentrated until 
they are strong brines, without producing the conditions necessary for the 
formation of thinohte. It is evident, therefore, that some element in the 
chemistry of the lakes on the western border of the Great Basin, in which 
they differed from their sister lakes to the eastward, determined tlie crystal- 
line form of the (calcium carbonate precipitated from them. This difference 
was most probably the greater richness of the western lakes in alkaline 
carbonates. 

It has already been pointed out that lithoid and dendritic tufa must 
have been deposited from the same solution under sliglitly varying condi- 
tions, for the reason that narrow bands of these varieties alternate with one 
another. A similar ahernation of tliinolite and dendritic tufa has been ob- 



214 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

served in many places, which seems evidence that these varieties were de- 
posited from the same waters under somewhat diverse conditions. A char- 
acteristic feature of inclosed lakes is their inconstancy of level. It seems 
evident that the banded character of the tufa deposits may be correlated 
with fluctuations of the lakes in which they were formed. In the case 
under consideration, we may reasonably assume that when the waters were 
concentrated, thinolite was crystallized ; when they became somewhat dilute, 
the tufa assumed the dendritic form. Finally the lake rose and remained 
for a long time above the thinolitic limit and only the dendritic variety was 
deposited. Our observations lead to the conclusion that the changes from 
conditions favoring the crystallization of thinolite to those admitting of the 
formation of dendritic tufa or vice versa, during certain stages of the lake, 
were very slight. It appears quite probable that the alternation of thin 
layers of these varieties of tufa may record alternate arid and humid peri- 
ods. That they are not annual growths, thinolite being formed during the 
summer and dendritic tufa during the winter, is evident from the fact that 
the quantity of calcium in even the thinner layers is too great to have been 
contributed to the basin within a single year. 

Professor Dana's studies have shown that thinolite is a pseudomorph, 
but what the antecedent mineral may have been still remains an enigma. 
Geological observations when considered by themselves tend to the hypoth- 
esis that the waters in which thinolite was formed were charged with sodium 
carbonate, and that the crystals now represented by the thinolite were a 
compound of soda and lime, presumably as the double carbonate. Professor 
Dana has shown, however, that this postulated mineral could not have been 
gaylussite (as supposed by King) and, in fact, was not any natural or arti- 
ficial crystal that has been recognized. It appears as if the unknown min- 
eral must have been produced by a delicate adjustment of the chemical con 
ditions of lake waters — in which the influence of the mass and of tempera- 
ture perhaps played an important part — which has not been observed in 
nature or reproduced in the laboratory. In reference to the chemical nature 
of the original mineral Professor Dana says : 

" The description of the original crystalline form of the thinolite, so 
far as it can be made out, is sufficiently complete to give an emphatic neg- 






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THINOLITE NOT A P8EUDOMORPH AFTER GAYLUSSITB. 215 

ative answer to the question as to the nature of the original mineral. It 
was not gayhissite, nor gypsum, nor anhydrite, nor celestite, nor gkiuberite, 
nor, in fact, any one of the minerals which might suggest itself as a solu- 
tion of the problem. The crystalline form is totally irreconcilable with 
any of these. This is so clear, from what has gone before, that the question 
admits of no argument at all. But more can be said: the original mineral 
was one which does not appear thus far to have been observed in its 
natural condition, although, as will be shown later, it probably has oc- 
curred abundantly at numerous other localities. Furthermore, a review 
of all the artificial salts of calcium, sodium, and magnesium has failed to 
bring to light any one which would satisfy the conditions required. 

"It seems, therefore, that any explanation of the original condition of 
the thinolite beds of Lake Lahontan must at present rest on hypothetical 
grounds, and much as a definite solution of the problem is to be desired, it 
is not now attainable. A few suggestions may not be out of place here, 

The open skeleton forms, consisting now of crystallized calcium 

carbonate, make it seem very probable that the original mineral was a 
double salt, and that a salt containing calcium carbonate as one of its 
members. Only on such a supposition is it easy to understand the removal 
of so large a part of the original material and the leaving behind of these 
plates of calcium carbonate, marking the original crystalline structure. 
Whether the original crystals were or were not solid throughout, at the 
time of their formation, it is not possible to say now with certainty; very 
probably they varied much at different points in this respect. From the 
analogy of soluble salt deposited rapidly from aqueous solutions, it seems 
likely that open, cavernous forms were common, perhaps the rule. But 
even supposing this to be true, no one can inspect such groups of skeleton 
crystals as those from the Marble Buttes without seeing that what now 
remains is only a part of what originally crystallized out of the saline 
waters of Lake Lahontan. This fact, coupled with the other just men- 
tioned, that the remaining skeleton consists of crystallized calcite in gran- 
ular form, gives, a very important hint as to the changes which these 
crystalline beds have undergone. The successive steps may have been as 



216 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

follows: (1) The deposition of crystals as the lake waters evaporated; (2) 
a change of conditions, e g.^ an addition of fresh water to the lake (as 
supposed by King), leading to the solution of a part of the substance of the 
crystals and the simultaneous recrystallization of the remaining calcium 
carbonate; (3) the subsequent and independent deposition of the car- 
bonate, solidifying and coating over the skeleton fonns.^ The conclusion 
reached by Mr. King, that the original mineral was gaylussite, satisfies the 
requirements tolerably well, for it is then necessary only to explain the 
removal of the sodium carbonate, and the calcium carbonate remains 
behind. Unfortunately for this hypothesis, it is impossible to reconcile 
forms which now remain, showing how the original mineral crystallized 
with the monoclinic forms of gaylussiteJ^ Furthermore, Mr. Russell finds 
several other grounds, independent of this crystallographic proof, for the 
belief that the supposed enormous deposit of gaylussite could not have 
taken place. But if not gaylussite, what was the original mineral? 

**It is hardly profitable to go beyond the above suggestion, that it 
may have been a double salt, containing CaCOa, unless the hypothesis can 
be bjised upon some observed facts; but fortunately some facts can be 
pointed to which lead to a possible explanation of the enigma, and which 
are in any case very suggestive 

" The only crystalline forms bearing any close resemblance to the acute 
tetragonal pyramids of the thinolite, of which the writer has any knowledge, 
are those of the pseudomorphs of lead carbonate after phosfjenite, first described 
by Krug von Nidda,^^ from the zinc mines in Upper Silesia. This simi- 
larity in habit and angle is the more striking, as the thinolite form is an 

» U. S, Geological Exploration of the Fortieth Parallel* Vol. I, p. 517. 

^^At the time wheu Mr. King had this suhjcct under investigation he submitted several speci- 
mens to the writer for inspection, and he tben gave a qualified assent to the conclusion Mr. King had 
reached in regard to them. One of these specimens, as Mr. King had noted, showed some crystals 
which bore a remarkably close resemblance to the well-known Sangerhanseu pseudomori)hs, then gen- 
erally referred to gaylnssite. This similarity suggested identity of origin — a conclusion which (after 
a further study of the same specimen) the present investigation has confirmed, as noted below — and 
thus gave apparent support to the gaylussite hypothesis. The other specimens then in hand were 
somewhat like Fig. 1, on Plate XXXIII, and upon the inspection given them— no opportunity was had for 
careful study — they gave negative results; a certain outward similarity to the elongated crystals t>f 
gaylussite from South America (called clavoSy nails) was note<l, but nothing more definite. 

^* Krug von Nidda: Ueber das Vorkomnien des Hombleierzos und des Weissbleierzes in den Krys- 
tallformen des ersteren in Oberschlosien, Zeitsch. geol. Oesellsch., II, 1*2«), 1850. See also Blnm, 
Pseudomorxihoseii, Zweitcr Nachtrag, 68. 



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ORIGINAL CHARACTER OF THINOLITB. 217 

unusual one. A number of these pseudomorphs are in the Blum collection, 
which became the property of the Yale Mineralogical Museum in 1872. 
They correspond to the description given by Krug von Nidda. They have 
the form of a square prism, sometimes terminated by a pyramid having an 
angle over the extremity of about 36°, and occasionally show traces of an 
octagonal pyramid ; other forms show only a very acute square octahedron, 
with a summit angle of about 13° in one case and 2(J° in another. One 
specimen shows these forms imbedded in a white clay. They aire now com- 
pletely altered to compact, fine-granular lead carbonate, except for the pres- 
ence of an occasional minute nucleus of the original mineral. 

'* The hypothesis to which this resemblance leads is this : that the orig- 
inal mineral may have heen chloro-carbonate of calcium isomorphous with phosge- 
nite ; that is, a mineral having the composition CaC03-|-CaCl2 isomorphous 
with PbC03+PbCl2, and now altered to CaCOg, as in the phosgenite to 
PbCOa. The liypothesis, as far as the crystallographic relations are con- 
cerned, is a most natural one. The diflSculty arises when we consider the 
peculiar nature of calcium chloride, and hence question whether an anhy- 
drous molecular compound of calcium carbonate and calcium chloride 
could have been deposited from the waters of Lake Lahontan. Obvi- 
ously this is a subject for synthetic experiment, and whatever the nature of 
the original mineral, it ought to be possible to approximate to the condi- 
tions under which it was made and so to reproduce it. It is to be hoped 
that the work now being carried forward by the chemists of the Geological 
Survey may lead to some decisive results in this direction. 

** In the meantime it is interesting to note the only case in which, so 
far as the writer can ascertain, a chloro-carbonate of calcium has been 
formed. The experiments are described by Fritzsche in the Bulletin of the 
St. Petersburg Academy for 1861, and reprinted in the Journal fiir prak- 
tische Chemie.'" He states that on evaporating the solution of crystallized 
calcium chloride, prepared in large quantities for technical purposes, there 
remained a small amount of a sandy powder, which kept a yellowish aspect 
80 long as the calcium chloride solution was concentrated, but in a dilute 

'^ J. Fritzsche: Ueber ein Doppolsalz ana kobleusaurem Kalk uod chlorocalciani. Jodf. prakt* 
Chem., LXXXUI, 210, 1861. 



218 GEOLCGICAL HISTORY OP LAKE LAHONTAN. 

solution became finally white. When some of the crystals were placed on 
a glass slide under the microscope, and then water poured upon them, it was 
observed that they for a moment were completely transparent and under- 
went no change ; soon, however, the surface became clouded, and then a 
granular separation took place gradually. As the CaCl2 was dissolved they 
entirely lost their transparency, and finally there remained only a skeleton of 
calcium carbonate corresponding in form and size to the original crystal. These 
fell to pieces when touched, and there resulted minute spherical masses of 
probably amorphous carbonate. This salt was found to have the composi- 
tion 2CaC08+CaCl2+6H20. The crystals were shown by v. Kokscharof to 
belong either to the orthorhombic or monoclinic system. It is not to be 
supposed that this salt of Fritzsche is in any way an explanation of the 
thinolite enigma, and yet his observations are of great interest in this con- 
nection. In order to complete the subject the fact may be noted that Ber- 
thier speaks of forming a compound of calcium-carbonate and chloride by 
fusion. 

" Another hypothesis may be oflfered as to the composition of the orig- 
inal mineral, viz: that it was a double salt of calcium and sodium, perhaps 
conforming to the formula CaCOs-f-NaCl, or better CaC03-|-2NaCl, which, 
it is possible, might also be isomorphous with phosgenite. This is so purely 
hypothetical that very little weight can be given to it ; still it may not be 
entirely useless to throw out the suggestion, although various serious objec- 
tions at once come up to mind. In any case it must be borne in mind 
that carbonates and chlorides were the salts most likely to be precipitated 
from the lake water, and calcium and sodium were the prominent basic ele- 
ments at hand." 

The crystals deposited on such an enormous scale in Lake Lahontan 
are considered by Professor Dana as being of the same nature as the well 
known Sangerhausen pseudomorphs Similar crystals have also been found 
at other localities, but for the discussion of these mineralogical relations we 
must refer the reader to Professor Dana's report, where these matters are 
considered at some length. 



TUFA A DEPOSIT OF WEAK BEINE8. 219 

Throughout the Lahontan basin the various deposits of tufa are most 
abundant on steep rocky slopes and on isolated buttes which were formerly 
submerged. Its exceptional abundance at these localities is due principally 
to the fact that the rocky surface afforded stable support for the precipitates 
deposited upon them; and its preservation is insured because precipitous 
shores are in general only slightly modified by wave action, and are not 
favorable to sedimentation. The dash of the waves against sea cliffs may 
also promote precipitation for the reason that the waters are aerated, thus 
facilitating the escape of carbon dioxide, the presence of which is necessary 
to the solution of calcium carbonate. Wherever tufa occurs on the surface 
of lake beds a solid nucleus may nearly always be found about which the 
calcium carbonate was deposited. Pebbles and shells lying on the bottom, 
or rocky points projecting above the mud, were favorable nuclei around 
which crystallization took place. About such centers mushroom-shaped 
growths were formed like those shown on Plate XXXVII, or domes and 
castles of great size were slowly built up. Solid nuclei seem essential for 
the commencement of these imitative structures, and appear to play the same 
role as the nuclei in the familiar experiments of crystallizing alum and rock 
candy. Some of the towers and castles in the Lahontan basin, which contain 
hundreds and even thousands of tons of tufa, are known to spring from small 
centers of accretion. When crystallization was once initiated, precipitation 
appears to have been accelerated and may possibly have been continued in 
waters that were below the point of saturation. When the crystallization 
began about a small nucleus at the bottom of the lake the tendency was to 
build upwards. Owing to this tendency the tufa deposited in isolated 
localities assumed the form of domes and towers instead of spreading out 
laterally and forming sheets or thin flat-topped masses. 

The fact that calcium carbonate cannot remain in solution in concen- 
trated lake waters, but is precipitated as soon as delivered by tributary 
streams, indicates that tufa is a deposit of moderately saline waters. In 
Great Salt Lake little more than a trace of calcium is found, and this prob- 
ably exists as the sulphate. In Mono Lake about six hundredths of one 
per cent, has been found by analyses. The dense alkaline waters of the 
Soda Lakes near Ragtown, and of Abert Lake, Oregon, are free from cal- 



220 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

cium; yet all of these lakes are fed by waters that hold about the normal 
amount (0.0088 per cent.) of calcium carbonate found in river waters. 
Wlien streams and springs enter these highly concentrated lakes, the cal- 
cium carbonate they hold in solution is at once precipitated, either in an 
amorphous or a crystalline condition, and accumulates at the bottom in 
the form of marl or, in some instances, as oolitic sand. In order that 
tufa may be deposited about the borders of a large lake it is evident 
that the calcium carbonate must remain in solution for a considerable time 
so that it may be carried to distant parts of the lake; hence the lake waters 
cannot be highly concentrated or else the calcium would be precipitated 
before reaching points situated at a distance from the mouths of the inflow- 
ing streams. From observation we learn that compact lithoid tufa is now 
being deposited in Pyramid and Walker lakes, which contain about three- 
tenths of one per cent, of total solids in solution. In the more highly con- 
centrated lakes mentioned in this paragraph, no deposits of tufa have been 
observed in process of formation. This evidently indicates that a lake in 
which heavy deposits of calcium carbonate were accumulated could not 
have been a concentrated solution during the tufa-forming sta-ges. The 
deposition of marl in lakes of concentrated water has not been observed, 
but it appears probable that the highly calcareous beds found in the sedi- 
ments of some of the Quaternary lakes of the Great Basin were precipitated 
from saline waters. The precise chemical conditions which determine 
whether the calcium carbonate precipitated from lake waters shall be 
incoherent and form marl, or whether it shall crystallize on coming in 
contact with foreign bodies or previously formed crystals has not been 
determined. Questions of this character are in a great measure beyond 
laboratory experiment for the reason that large bodies must be dealt with 
in order to reproduce the conditions of nature. 

That the shells of mollusks occur in thousands in both the lithoid and 
the dendritic tufa, is also proof that the waters of Lake Lahontan were only 
moderately concentrated at the time these deposits were formed. No traces 
of fossils have been found in the thinolite crystals. 

When springs rise in the bottom of a lake a new element is introduced 
into its chemical history. Sublacustral springs, charged with carbon dioxide 



SUB-LACUSTRAL SPRING DEPOSITS. 221 

and calcium carbonate, upon mingling with the waters of a lake may part 
with their dissolved gases and deposit calcareous tufa. Agahi, the waters 
of a lake may be such a strong brine that calcium carbonate cannot be 
retained in solution, as is the case with Great Salt Lake at the present time. 
In such an instance the calcium carbonate contributed by springs would be 
precipitated when their waters mingled with those of the lake. Phenomena 
of this nature have been observed at the Needles, as described on page HI, 
and may be studied at a number of localities in Mono Lake. This lake, as 
shown by the analyses given on table C, is a strong solution of the car- 
bonate and the sulphate of soda, chloride of sodium, etc., while many of the 
springs that rise in it are quite remarkable for their purity, but yet contain 
a small percentage of calcium carbonate wliich is deposited about their 
pomts of discharge. These accumulations frequently form domes of large 
size that are porous nnd tubular in structure, and in many respects resemble 
those standing in the deserts of the Lahontan basin. In numerous instances 
the deposits from the springs in Mono Lake form irregular tubes that are 
clustered together and frequently branch and expand as they grow upwards, 
thus forming columnar and vase-shaped structures. A most instructive 
exhibit of this nature is to be seen in the western portion of Mono Lake, near 
the mouth of Mill Creek. At this locality, a part of which is shown in 
Plate XLTIT, tliere are as many as fifty or sixty tufa domes standing in 
from twelve to fifteen feet of water, many of which rise from ten to twelve 
feet above the surface of the lake. The tops of some of these structures 
are occupied by basin-sliaped depressions, which in a few instances, are 
filled with water that rises througli the in*egular tubes and open spaces in 
the column beneatli. The water in these basins is cool and fresh, and over- 
flowing, fountain-like, down tlie sides of the vases, mingles with the waters 
of the lake. These structures are still growing by the gradual precipitation 
of calcium carbonate, which is taking place, however, only above the lake 
surface. They are nearly always considerably smaller at the lake surface 
than at the top, and in general form are not uidike the sponges known as 
Neptune's cups, found in southern seas They are not only striking 
examples of chemically formed rocks that are of interest to the geologist, 
but they are fountains of sweet water in the midst of a lake that is utterly 



222 



GEOLOGICAL HISTORY OF LAKE LAUOBTTAN. 



unfit for drinking. In some instances tufa towers ten or twelve feet in 
diameter, perhaps occurring in clusters, rise twenty or thirty feet above the 
bottom where soundings show the water to be forty feet deep. From a boat 
these structures may be clearly seen when sailing over their submerged 
smnmits. At times springs rush upward from openings in the tops with 
such force that their presence is distinctly marked at the surface by a low 
dome of water. 

The formation of tufa finds many illustrations in the Mono basin 
which will be described more completely in a future report. Only a few 
examples are mentioned here as supplementing those observed in the 
Lahontan basin. On the southern shore of Mono Lake, near the Mono 
Craters, there is an area several acres in extent, bordering the lake, that is 
covered with thousands of slender tubular columns of tufa from a few 
inches to three or four feet in height. These are porous and tabular in 
structure, and must have been built up by the deposition of calcium car- 
bonate from the waters that once rose through them. When the orifice at 
the top of a column became closed other openings were formed at the side, 
thus causing the structure to become irregular and sometimes branching. 
This strange forest of contorted tufa trunks was formed by springs beneath 
' the surface of the lake when it stood at a higher level than at present, and 
lias been left exposed by a recession of the waters. 

The similarity in structure between the tufa deposits formed about 
sublacustrat springs in Mono Lake, and the inner core of Htboid tufa in 
many of the tufa towers now standing in the desiccated basin of Lake 
Lahontan, is sufficient indication that many of the latter were deposited in 
a like manner. This explanation, however, cannot be extended to the 
coatings of thinolite and dendritic tufa enveloping the cores of lithoid. 
From our present knowledge we may conclude that there are at least two 
ways in which tufa towera may originate. First, by the direct precipita- 
tion of calcareous tufa about nuclei. Second, from the precipitation of the 
same material from springs rising in lakes that are highly charged with 
mineral matter in solution. 



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FEBSHENING OF LAKES BY DESICCATION. 223 



Section 3.— DESICCATION PRODUCTS. 

During the centuries that witnessed the deposition of the vast amount 
of calcareous tufa now found in the Lahontan basin, other salts were 
contributed to the lake in varying proportions. Upon the evaporation of 
the waters these more soluble salts were eventually deposited, and, as the 
lake never overflowed, they must still be retained in the basin. 

Instances of the deposition of salts by the evaporation of inclosed 
lakes are common, and may be illustrated by many examples in the Great 
Basin. The salt fields in Osobb Valley; the saline deposits left by the 
evaporation of the Middle Lake in Surprise Valley, California, in 1872; 
and by the broad salt field now covering the desiccated basin of Sevier 
Lake in Utah, are all cases in point 

In the Lahontan basin, deposits of this character, which have resulted 
directly from the evaporation of the former lake are nowhere to be found. 
The accumulations of common salt, sulphate of soda, etc., occurring in 
considerable quantities at certain localities, have in all cases been deposited 
since the evaporation of the foniier lake. In some instances these accumu- 
lations are due to the leaching of saline clays, and the evaporation of 
the resultant brine in restricted areas, as in the case of the salt fields in 
Alkali Valley; at other times saline deposits of considerable thickness 
have resulted from the evaporation of spring waters. Over very large 
areas the Lahontan beds are frequently whitened with a saline efflorescence, 
which also owes its accumulation to secondary causes, as will be described 
a few pages in advance. 

Wherever the Lahontan sediments have been examined they have 
been found more or less highly charged with salts of the same character as 
those that were most common in the waters of the former lake. The total 
quantity of saline matter thus imprisoned is certainly very great, and is 
assumed to represent the more soluble substances contributed to Lake 
Lahontan. 



224 GBOLOCIICAL HISTOEY OF LAKE LAHOi^TAN. 



THE FRESHENING OF liAKES BY DESICCATION, 

The apparently anomalous phenomena of the desiccation of a great 
lake without leaving a surface deposit of salt, seems explicable in only one 
way. Adopting the suggestion advanced by Mr. Gilbert in explanation of 
some portion of the history of Lake Bonneville, the absence of saline 
deposits is accounted for by the hypotliesis that they were buried and 
absorbed by lacustral clays and playa deposits during periods of desiccation. 

The freshening of a lake by desiccation may be illustrated in all its 
stages in the various basins that have been examined in the Far West. 
A lake after a long period of concentration becomes strongly saline, and 
finally evaporates to dryness, leaving a deposit of various salts over its 
bed. During the rainy season the bottom of the basin is converted into a 
shallow lake of brine which deposits a layer of sediment; on evaporating 
to dryness, during the succeeding arid season, a stratum of salt is deposited 
which is, in its turn, covered by sediment during the succeeding rainy 
season. This process taking place year after year results in the formation 
of a stratified deposit consisting of salts and saline clays in alternating 
layers. The saline deposits may thus become more and more earthy jintil 
the entire annual accumulation consists of clays. The site of the former 
lake then becomes a playa. . A return of humid conditions would refill a 
basin of this character, and might form a fresh-water lake, the bottom of 
which would be the level surface of the submerged playa. 

The larger lakes of the Lahontan basin, as well as a number of less 
importance in eastern Nevada and southern Oregon, are without outlet 
They occur in basins that in almost all cases were occupied by much 
larger water-bodies during the Quaternary, which, like their modern repre- 
sentatives, never overflowed. From the long period of evaporation that 
has taken place, one would expect the existing lakes to be dense mother- 
liquors. The fact is, however, that they are but slightly charged with 
saline matter, and in some instances are sweet to the taste and sufficiently 
fresh for all culinary purposes. In many localities the lacustral beds sur- 
roundiiig and underlying the present lakes are highly charged with soda 
salts, which rise to the surface during the dry season as efflorescences. 



FEESHENING OF LAKES BY DESICCATION. 



225 



As these lake basins were never filled to overflowing, we are forced to 
conclude that influx was counterbalanced solely by evaporation, and that 
during periods of extreme desiccation the saline deposits became buried 
and absorbed by the marls and clays which accumulated in the valleys. 

Having analyses of the waters of an inclosed lake, and knowing also 
the composition of its tributaries, we can determine, at least approximately, 
the length of time it has been in existence, provided no salts previously 
deposited were dissolved when the basin commenced to fill. For the 
purpose of making a computation of this nature in the case of the lakes 
now occurring in the Lahontan basin, the following table has been com- 
piled from analyses given in chapter III. 

Table D. — Composition of the principal lakes and rivtrs of the L<ihontan haain, 

LAKBS. 



Pyramid 

Tn 1,000 parts of water. I (average of 

'4 analyses). 



Silica (8iO>) 

Calciam (Ca) 

Magnesiom (Mg) 

PotassliUD (K) 

Sodium (Na) 

Salphoric acid (SO4) 

Chlorine (CH 

Carbonio acid (CO3) by differ- 
ence 



0.0334 
0.0080 
0.0707 
0.0783 
1.1706 
0.1822 
1.4300 

0.4000 



Total. 



8.4861 



Walker 
(average of 
2 analyses). 


Winnemnoca. 


0.0075 


0.0275 


0.02215 


0.0106 


0.0383 


0. 0173 


trace 


0.0686 


0.85535 


1.2070 


0.5200 


0.1333 


0.58875 


1.6934 



0.47445 



0.3458 



2.50150 



3.6025 



Average. 

0.02280 

0.01688 

0.0451 

0. 04730 

1.11065 

0.2785 

1.23488 

0.43075 



Probable combination in average oompo* 
aition. 



3.10586 



Silica (SiO>) 

Calcium carbonate (CaCOs) . 
Magnesium carbonate (Mg 

C0») 

Sodiam carbonate (NaCOs) . . 
Potassium chloride (KCl) . . . 

Sotliuni ( hloride (NaCl) 

Sodium sulphate CNa«S04) .. 

Total (00.00 percent ao- 
counted for) 



a 02517 
0. 03221 

0.20488 
0.48827 
0.09604 
1.04244 
0.40196 



8.18881 



lOVBRS. 



In 1,000 parts of water. 



Silica (SiO») 

Alumina ( AlsOs) 

Calcium (Ca) 

Magnesium (Mg) 

Potaasium (K) 

Sodium (Na) 

Sulphuric acid (SO4) 

Chlorine (CD 

Carbonio acid (COs) by differ 
ence 

Total 



Humboldt 



0.0326 
0.0013 
0.0480 
0.0124 
0.0100 
0.0467 
0.0477 
0.0075 

0.1544 



0.8615 



Truckee. 



0.0187 



0.0093 

0.0030 

0.0033 ; 

0.0078 

0.0054 

0.0023 

0.0287 



0.0730 



Walker. 



0.0225 



0.0228 
0.0088 
trace 
0. 0318 
0.0284 
0. 0131 

0.0576 



0.1800 



Average. 



0.0220 
0.0004 
0.0270 
0.0064 
0.0044 
0.0286 
0.0271 
0.0076 

0.0802 



0.2046 



Probable combination in average compo- 
sition. 



Silica (SiOi) 

Alumina (AUOs) 

Calcium carbonate (CaCOa) . 
Magnesium carbonate (Mg 

C0«) 

Sodium carbonate (NaCOa) ■ ■ 
Potassium carl)ouate (KCOg) 
Potassium chloride (KCl) . . . 
Sodium chloride (NaCl) . . 
Sodium sulphate (NasSOi) . . 
Potassium sulphate (KsS04) ■ 

Total (00.08 per cent ac- 
counted for) 



0.0219 
0.0094 
0.0e76 

a0824 
0.0294 
0.0015 
0.0064 
0.0076 
a0808 
0.0011 



0.197S 



MON. XI 15 



226 GEOLOGICAL HISTORY OF LAKE LAHONTAN, 

Commencing with the simplest instance, we have in the case of Walker 
Lake an inclosed water-body which receives its entire supply from the 
Walker River. The total quantity of saline matter contained in the lake 
water is 13.89 times as great as in an equal volume of river water. It fol- 
lows, therefore, that nearly fourteen times the present volume of Walker 
Lake has been evaporated in order to bring the waters to their present 
degree of salinity. If we know the average annual influx, we can deter- 
mine the length of time required to bring the lake to its present density. 
From the very few measurements available, we have assumed 200 cubic 
feet per second, or 700,000,000 cubic yards per annum, as the average dis- 
charge of the Walker River at the present time (see page 44). The vol- 
ume of the lake, as determined from the data given on Plate XV, is 
13,159,000,000 cubic yards. It would therefore require between eighteen 
and nineteen years for the river to supply water enough to fill the lake 
basin to its present extent. As the total saline content of the lake amounts 
to about fourteen times what would be contained in an equal bulk of 
river water, it would require 260 years for the river, with its present vol- 
ume, to supply the amount of saline matter now dissolved in the lake, 
provided there had been no loss of the salts contributed. Observations 
have shown, however, that calcium carbonate is being deposited from the 
waters of the lake. A comparison of the analyses of the lake and river 
waters given on pages 46 and 70, shows that there is even less of this 
salt in the lake than in an equal volume of the river water. All of the 
calcium now contributed is apparently at once precipitated. The remain- 
ing salts occurring in the lake are more soluble than calcium carbonate, 
and we have no reason to suppose that any of them are being precipitated. 
Dropping calcium carbonate from the analyses, and considering the re- 
maining salts only, we learn that in these the lake is 19.66 times as rich as 
the river waters. Making the computation as before, but using the last 
mentioned value for the relative salinity of the lake and river, we find that 
it would require 343 years for the river to supply the amount of salt now 
contained in the lake. 

Approaching the question in another manner, it is evident that we may 
determine the annual inflow, providing the annual evaporation is known. 



FEBSHENING OF LAKES BY DESICCATION. 227 

for the reason that the inflow and the evaporation now counterbalance each 
other. There are no observations on the rate of evaporation in this region, 
but in a similar calculation relating to Great Salt Lake, Mr. Gilbert, after 
considering all the data available, has assumed 6 feet per annum as the loss 
by evaporation. In the comparatively fresh waters of Walker Lake the 
rate of evaporation under the same atmospheric conditions must be consider- 
ably greater than in the nearly saturated brine of the Utah Lake. In order 
not to overestimate, however, we will assume the same rate of evaporation 
in Walker Lake that has been adopted in the case of Great Salt Lake, viz., 
6 feet per annum. The area of the lake is 118 square miles, or 365,516,800 
square yards; an annual loss of 6 feet by evaporation gives 731,000,000 
cubic yards as the total annual evaporation. This estimate was made inde- 
pendently of the former, but the data in each case are necessarily indefinite, 
and the close approximation in results is not an indication of accuracy. 

The average depth of Walker Lake is 118 feet, and as the waters are 
19.66 times as saline as those of the river, omitting calcium carbonate from 
each, it would evidently require the evaporation of a lake of fresh water 
of the present size and 2,320 feet deep to produce the amount of saline 
matter now held in the lake. Evaporation taking place at the rate of 6 feet 
per year, it would require 370 years to reduce this hypothetical lake to the 
present volume of Walker Lake. Before drawing any conclusions as to the 
length of time that the present lakes of the Lahontan basin have existed, 
we may make a more general calculation of the same nature as the above. 

Let us suppose the three principal lakes of the Lahontan basin united, 
and supplied by the three rivers of which we have analyses, viz., the Hum- 
boldt, the Truckee, and the Walker. We should have a lake 1,300 square 
miles in area, with an average depth of 1 1 7 feet, and containing 26.7 1 times the 
percentage of salt held by the average of the tributary streams, not includ- 
ing CaCOg. To obtain a water-body of this degree of salinity from the 
concentration of the river-waters would require the evaporation of a lake of 
the area of the assumed one and 3, 125 feet deep. Evaporation taking place 
at the rate of six feet per year, it would require 521 years for the waters to 
be condensed to the degree represented by the present lakes. This estimate 



228 GEOLOGICAL HISTOUY OF LAKE LAHONTAN. 

has been made without considering the amount of saline matter brought 
into the hikes by springs ; and assumes that no salts remained in the basin 
when the process began. We know, however, that very large quantities of 
various salts are contributed to the lakes of the Lahontan basin from sub- 
terranean sources. Anj conclusion derived from the above considerations 
must be weighted by the fact that the analysis of the rivers were in all 
cases of samples collected outside the old lake basin, and therefore not 
aflfected by the substances derived from the richly saline clays and marls of 
Lahontan date, through which they carved channels sometimes a hundred 
miles in length before reaching the lakes into which they empty. The 
present lakes also derive large quantities of foreign matter from the tem- 
porary rills that are formed after the infrequent storms and are charged with 
the salts derived from the efflorescences formed on the surrounding desert 
surfaces during the arid season. It is true that the data we have used for 
computing the flow of the rivers as well as for obtaining the average annual 
evaporation are based upon very incomplete observations, but we feel con- 
fident that future study will show these estimates to be below rather than 
above the reality. With all these considerations in view, it seems evident 
from the calculations we liavo made, that the lakes of the Lahontan basin 
could not have existed under the i)resent conditions for more than a few 
centuries at the most without being far more saline and alkaline than we 
now find them. From the hypothesis of the freshening of lakes by desic- 
cation we conclude that the basin of Lake Lahontan was completely desic- 
cated for a i>eriod, ending, we will say, about three hundred years ago, which 
was sufficiently long to allow of tlie burial of any saline deposits that may 
have been left from the evaporation of previous water-bodies in the same 
basin. By complete desiccation we mean that the various secondary basins 
formerlj'- flooded by Lake Lahontan became sufficiently dry during success- 
ive years, or at intervals of a number of years, to admit of the formation 
of playa-lakes and play as, arid the burial and absorption of saline matter 
beneath playa deposits. That this was the actual condition of the various 
valleys composing the Lahontan basin at no distant date is rendered still 
more probable by the fact that the bottoms of all the lakes of the region 



FRESHENING OF LAKES BY DESICCATION. 229 

are level-floored, and have the same general contour as many neighboring 
valleys which are occupied by playas/^ 

Applying this line of argument to all the inclosed lakes of the Great 
Basin, we find, with the exception of Great Salt and Sevier Lakes — the 
Soda lakes near Ragtown, Nevada, and Mono Lake, not being considered, 
as they are of an exceptional character — that there is not a lake among the 
number that could have undergone the present rate oi concentration for 
more than a very few centuries witliout being far more saline than we now 
find it. By consulting Table C, it will be seen that with the exceptions we 
have mentioned there is not a lake in the arid region of the West that con- 
tains more than one-fiftieth of the quantity of the more common salts nec- 
essary for saturation. This appears to be prima facie evidence that these 
lakes have undergone some process by which their salts have been elimin- 
ated within very recent times. In the case of Great Salt Lake we find an 
exception not only in the amount of saline matter it holds in solution, but 
also in its environment. With this exception, all the lakes of the Great 
Basin occupy narrow valleys in which a lake on evaporating would deposit 
its salts in a comparatively restricted area, thus favoring their burial by 
playa deposits. The basin of Great Salt Lake, on the other hand, is not 
only of broad extent, but receives its entire water supply from one side, and 
is thus unfavorable in its topographical relations for the burial of products 
of desiccation beneath playa deposits. The present density of this lake 
may therefore be due to the fact that its salts were not buried during a 
time of desiccation which admitted of this result in smaller basins ; conse- 
quently, when the valleys were reflooded, the lakes in the smaller basins 
were fresh, while in the larger one the unburied saline deposits left by the 
evaporation of the former lake were redissolved. 

The order in which a number of inclosed lakes in an arid region like 
the Great Basin, will become dry during a time of more than usual desic- 
cation, depends on many conditions ; one of the most important of which 
is the ratio of evaporating surface to elevated catchment basin A lake 
whose hydrographic basin is low will be extremely sensitive to climatic 

^A comparison of the lake basinH of the Lahontan region with the depressions holding the Laa- 
rentian lakes, shows that the bottoniH of the former are more nearly horizontal and far more regular 
than those of the latter. 



230 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

oscillations ; while one receiving the drainage from a lofty mountain range 
may be but slightly lowered by a cHmatic change that would produce des- 
iccation in a neighboring valley. From this and other allied reasons, Great 
Salt Lake may not have been evaporated to dryness during the time that 
the lakes of western Nevada completely disappeared. 

The only analysis we have of the waters of Sevier Lake gives 8.64 
per cent, as the total of saline matter in solution. The sample analyzed 
was collected in 1872 ; ten years later the lake was almost completely des- 
iccated, and its site converted into a field of salt. We have classed this as 
a playa lake, and do not consider it of importance in the present discussion? 
as it not only varies greatly in salinity, owing to variations in volume, but 
is also so situated that it receives the drainage of a broad desert and must 
receive large quantities of saline matter from the efflorescences formed each 
year on the neighboring land surface. 

A comparison of the moUuscan life of Pyramid and Walker lakes with 
Lahontan fossils indicates that a marked change has taken place in the 
fauna of the basin since the last high-water stage of the old lake. This 
question is considered in the chapter devoted to the life history of Lake 
Lahontan. 



Section 4.— EFFLOEESCENCES. 

In the preceding pages we have had occasion to speak of the saline 
incrustations, or efflorescences, to be seen over large areas in the Lahontan 
basin. It is now our purpose to describe these accumulations more fully. 
They originate in the saline lacustral clays which floor all the valleys once 
occupied by the ancient lake, and usually occur in greatest abundance on 
the borders of the larger deserts, where they not uncommonly whiten the 
surface over many square miles. In tracing their distribution it is notice- 
able that they occur most abundantly in those portions of the valleys that 
are underlaid by the clays deposited directly from suspension in the ancient 
lake, but are not found on the surfaces of many of the more modem playas 
which occupy the lowest depressions in the various basins, thus showing 
that the recently formed playa-beds are in many instances less saline than 
the true lacustral clays. 



EFFLORESCENCES. 



231 



The genesis of the efflorescent salts that appear on desert surfaces is not 
difficult to explain. During the rainy season the clays become saturated 
with moisture, but on the advance of summer they dry at the surface at 
the same time that moisture rises from below through the action of capillary 
attraction. The waters saturating the beds are rendered saline by the salts 
they dissolve from the clays, and on evaporating at the surface deposit all 
foreign matter as a surface incrustation. The incrustations thus formed 
are frequently five or six inches in thickness. They frequently dissolve and 
disappear during the winter, only to reappear when the heat of summer dis- 
sipates every drop of moisture from the surface of the deserts. 

From the manner in which saline efflorescences are formed, it is evident 
that they give a very fair indication of the character of the more soluble 
salts impregnating the lacustral beds which floor the valleys. The anal- 
yses inserted below are of representative samples gathered on the surface 
of the deserts at widely separated points in the Lahontan basin, and may 
be taken as indicating approximately the relative abundance of the more 
soluble salts in the sediments of the ancient lake. Local variations occur, 
but in general they consist mainly of the more common salts of soda, as 
has been shown by qualitative tests of a large number of samples in addi- 
tion to the quantitative analyses here introduced,'^ which were made by 
Dr. T. M. Chatard. Sample No. 1 is from the surface of the desert, a few 
miles north of the northern end of Walker Lake. No. 2 is from near Black 
Rock Point in the Black Rock Desert. Efflorescent incrustations are nearly 
always mingled with portions of the sand and clay on which they rest, but 
in the following analyses only the portion soluble in water is considered : 



Constitaents. 



SUica(SlaO) 

PoUssium chloride (KCl) . 
Sodium chloride (NaCl) . . . 
Sodium borate (Na2i}407) . 
Sodioin salphate (NasS04) . 
Sodiam carbonate (NaCOs) 



Nal. 


No. 2. 


Pereent 


Percent 


1.96 


2.18 


1.18 


1.89 


2.53 


59.82 


4.15 


1.00 


17.49 


27.05 


72.69 


9 06 


100.00 


100.00 



T^ See also Ueports of U. S. Geological Exploration of tke Fortieth Parallel, Vol. I, Table of ohem- 
leal analyses, No. V. 



232 GEOLOGICAL HISTOKY OF LAKE LAKONTAN. 

The total quantity of saline matter occurring as an eflBorescence on 
the deserts of the Lahontan basin would be found very great could it be 
reckoned in tons. At many places it is of economic importance for the 
common salt, sodium carbonate, boracic acid, etc., that it contains. The 
industries arising from the commercial value of these deposits, although 
limited at the present time, may be increased, at least so far as the gather- 
ing of common salt is concerned, almost without limit, the supply in many 
localities being far beyond any demands that are likely to be made upon 
ihem. 

A good illustration of the nature of the salts impregnating the Lahontan 
sediments is furnished by an examination of the various salt-works located 
within the lake basin. 

BUFFALO SPRINGS SALT WORKS. 

At the Buffalo Springs Salt Works, situated on the west side of Smoky 
Creek Desert, the brine from beneath the desert is allowed to collect in wells, 
and is then pumped into vats at the surface and left to evaporate. The crust 
of salt that remains is then gathered and is found sufficiently pure for all 
domestic uses. About 250 tons are annually collected, the total amount 
produced since the works were started being not far from 1,500 tons. When 
fresh water is caused to flow over the surface of lake-beds in the vicinity 
it soon becomes strongly saline, and when it gathers in hollows and evap- 
orates it leaves a crust of salt that is sometimes several inches in thickness. 
This method is employed, to some extent, for obtaining the less pure grades 
used principally for chloridizing silver ores 

Two miles east of the works there are level, pond-like areas on the 
surface of the desert that are usually covered with a white efflorescence 
some inches in thickness. Other depressions are soft and completely sat- 
urated with bitter brine. In some, there are deposits of sulphate of soda at 
least several feet in thickness, but never probed to the bottom. When 
examined by the writer, these sulphate beds weie covered to the depth of 
several inches with mother-liquor or soft mud that rendered the surface 
unsafe to walk upon. The whole desert region, on the edge of which the 



; 



SALT INDUSTRY. 233 

Buffalo Salt Works are situated, is one vast stretch of yellowish mud, with- 
out vegetation, impassable except during the dry season, and locally known 
as the '*mud lakes." The salt obtained from the wells of the salt works 
and the sulpliate of soda, and other minerals found on the surface near at 
hand, are all derived from the salts impregnating the Lahontan Lake beds. 
The brine from the wells has been analyzed by Mr. F. W. Taylor, of 
the National Museum, with the following result : 

Specific gravity, 1. 1330. 

Silica in solutiou trace 

Calcinm sniphate 0. 1467 

Magnesium sulphate .8833 

Potassium sulphate . 3111 

Sodium sulphate . 5306 

Sodium chloride 14.8383 

Water 8:^.2900 

100.0000 
BAGIiE SAI.T WORKS. 

Another locality favorable for the study of the desiccation products of 
Lake Lahontan is at the Eagle Salt Works, situated near the Central Pacific 
Ra,ilroad, about 1 8 miles east of Wadsworth. The long valley in which 
they lie was a strait during the higher stage of Lake Lahontan. When the 
water fell about 1(;0 feet the region where the salt is now found became a 
bay, connected with the Carson division of the lake through the Ragtown 
Pass. The country about the works is a desert mud plain, much of which 
is covered during the summer by a white saline efflorescence. The method 
here employed for obtaining the salt is to dissolve the crust that is formed 
on the surface of the desert and allow the saturated water to gather in shal- 
low vats and evaporate. The water from springs on the eastern edge of the 
plain is conducted over the surface of the lake-beds, and made to flood 
small areas inclosed by low dams or ridges of clay. From the flooded areas 
it soaks through the clay ridges and enters shallow vats dug in the lake- 
beds on either side, where it evaporates and deposits its salts. The areas 
inclosed by clay ridges and flooded by the fresh water are called ** reservoirs'' 
by the workmen, and the long troughs between them, where the brine evap- 



• I 



I 
I 



I i 



1 



I 



I 



234 GEOLOGICAL HISTOEY OF LAKE LAHONTAK 

orates, are known as "vats." These are arranged alternately and may be 
multiplied to any extent. A profile through a reservoir and the vats on 
either hand is shown in the diagram. 

Vat Ruervoir. YoL 




Fio. 30.— Section of reservoir and vaU at Eagle Salt Works, Nevada. 

The lake deposit here is a fine greenish mud or clay, and is so com- 
pletely saturated with brine that a thick crust is formed on the surface by 
efflorescence every dry season. The salt, being supplied from the beds be- 
low the surface, is renewed every summer, thus allowing a series of crops 
to be gathered from the same ground. 

A sample of brine from a vat in which the salt had begun to crystallize 
was analyzed by Mr. Taylor, with the following result : 

Specific gravity, 1.2115. 

Silica (insoluble) 0028 

Irou and alumina (insoluble) 0004 

Calcium sulphate 2897 

Calcium chloride 3578 

Magnesium chloride 3787 

Potassium chloride 0023 

Sodium chloride 25.3793 

Water 73.5890 

100.0000 

The annual yield of salt during the past ten years is reported to have 
been about 2,500 tons. The production has been determined solely by the 
demand. The amount that could be collected by the simple process of leach- 
ing the saline lake-beds and evaporating the saturated waters is practically 
without limit. 

SAND SPRING SAI^T WORKS. 

The most instructive salt field in the Lahontan basin is situated at the 

eastern end of a long, barren valley, joined to the Carson desert on the 

\( ' southeast by a narrow pass, and known as Alkali Valley. The floor of this 

valley, when left dry by the evaporation of Lake Lahontan, had the same 
general level as the Carson desert, and the lake-beds may be traced through 
the pass from one desert to the other. In riding from the Carson desert 
eastward into Alkali Valley, one conies to a line crossing Alkali Valley from 



SALT INDUSTRY. 235 

north to south, beyond which the surface of the desert has a gentle inclina- 
tion eastward. The surface of the lake-beds when first deposited was hori- 
zontal, and the present inclination is due to a fault crossing the valley with 
a north and south strike, and to the tilting of the orographic block on which 
the eastern portion of the valley is situated. The tilting of the floor of the 
valley resulted in the establishment of a drainage to the eastward for the 
surface waters, and the formation of a small lake at the eastern end of the 
valley near Sand Springs. During the winter the water collects there, form- 
ing a sheet of brine of variable size, sometimes covering 10 or 15 square 
miles of surface, but with a depth of only a few inches. In the summer 
the water evaporates and adds to the layers of salt previously deposited. 

The deposit of salt thus accumulated is from 3 to 5 inches thick near 
the margins, and is said to have a depth in the central portion of the basin 
of not less than 3 feet. It is gathered by simply shoveling it into baiTOWS 
and wheeling it out on to firm ground, where it is piled in huge heaps ready 
for transportation. 

The surface of the inclined lake-beds draining to the salt fields is abso- 
lutely destitute of vegetation, and usually exhibits no saline efflorescence, 
since this is dissolved away to supply the salt field. The soil, like that be- 
neath the accumulated salt, is a fine, greenish, saline clay, and may be 
readily examined in the sides of drainage channels, which score the sloping 
surface to the depth of 3 or 4 feet. 

The method here arranged by nature for dissolving the efflorescent 
salts from the surface of the lake-beds and evaporating the sahne waters in 
the restricted basin is practically the same as that employed by man on a 
smaller scale at the Eagle and Desert Crystal Works. 

Associated with the salt obtained at the various salt works are greater 
or less quantities of the borate of soda and the borate of lime, and in some 
cases, as at the borax works in Alkali Valley, they attain such importance 
as to afford a considerable quantity of borax There are many other local- 
ities in the Lahontan Basin where the chloride, the borate, the sulphate, 
and the carbonate of soda exist, sometimes in large quantities, in the in- 
crustations that form on the deserts, but at present the demand is not suffi- 
cient to warrant the working of these deposits for economic purposes. 



I ' 

I 



I, 

, I 
■ I 

I 



I 



I ■ 



1/ 



236 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



EfiSUME OF CHEMICAL HISTORY. 

The fluctuations of Lake Lahontan, so far as we have been able to 
determine from the study of its chemical records, may be briefly summar- 
ized as follows: 

The waters first formed a fresh-water lake having approximately the 
outline represented on the accompanying map^^ — which indicates the 
extent of the lake at the highest stage of all — and then evaporated away 
with many minor oscillations, until a greater degree of desiccation of the 
basin than the present was attained. During this oscillation the waters 
were saturated with calcium carbonate and deposited vast quantities ot 
lithoid tufa. 

Whether the lake evaporated to dryness or not during the time inter- 
vening between the formation of the lithoid and thinolitic tufa remains un- 
determined. . The contrast in the character of the tufa formed before and 
after this event is thought to indicate a partial evaporation, or perhaps 
complete desiccation, with the burial of the less soluble salts This is the 
inter-Lahontan period of desiccation. 

The waters next rose to about the level of the thinolite terrace, with 
many fluctuations, and formed at least two and probably three independ- 
ent water-bodies, which were more highly charged with saline matter than 
during the first expansion. From this solution, which was probably nearly 

identical in the various basins, the mineral after which the thinolite is a 
pseudomorph was crystallized. 

The thinolitic stage was closed by a rise of the lake. The waters 
were diluted, but probably still contained a larger per cent, of saline matter 
than during the lithoid stage, and the third or dendritic variety of tufa was 
deposited on an immense scale, but did not attain as great an elevation on 
the sides of the basin as the first formed tufa. 

During these three major oscillations there were many minor fluctua- 
tions of level, as is proven by the large number of variations in the tufas 
formed. 

After the precipitation of the dendritic tufa the lake rose higher than 
ever before, the evidence being furnished by gravel embankments, terraces, 

^'^In pocket at end of volume. 



EfiSUMlS OF CHEMICAL HISTOEY. 237 

and sedimentary deposits (see Cbap. IV), and then evaporated away prob- 
ably to complete desiccation. 

During this last subsidence a thin coating of coral-like tufa was 
formed, followed by the crystallization of a comparatively limited quantity 
of thinolite. 

When the lake approached complete desiccation after the post-den- 
dritic rise, it became divided into a number of independent areas, as during 
the inter-Lahontan subsidence. It is presumed that all these basins 
became completely desiccated, probably for a long term of years, and that 
the salts precipitated were buried beneath playa deposits so completely that 
when some of the basins were partially refilled, the salts were not redis- 
solved. This period of desiccation — as determined by calculating the time 
that would be required for the existing lakes to attain their present de- 
gree of saHnity — is thought to have terminated not more than three hun- 
dred years since. 



Flo. 31.~Carve exhibiting the rise and fall of Lake Lahontan: a a, deposition of lithoid tnfa; 6, deposition of thinolitic 
tnfa; e, deposition of dendritic tufa. Tbe flgnres indicate, in feet, the fluctuatious of the uncieut lake above and be- 
low the 1882 level of Pyramid Lake. 

If we project the fluctuations of Lake Lahontan in a curve (Fig. 31), 
the ordinates representing depths of the lake at various stages, and the 
abscissas succession in time, we find there are two maxima and two minima. 
We know that the first of the two high-water periods was the longer con- 
tinued, for the terraces the waves then cut in the rocks are broader and 
more strongly marked than the terraces recording the second rise. The 
second high-water period was of shorter duration, but the lake rose to a 
higher level than at the first filling. 

The salts impregnating the Lahontan sediments, which are now car- 
ried to the surface as efflorescences, are believed to have been absorbed 
fi-om the waters of the ancient lake by tlie clays and marls forming its 
bottom, when the lake was greatly concentrated by evaporation. 



CHAPTER VI. 

LIFE HISTORY OF LAKE LAHONTAN. 

The fossils obtained from the sediments and tufa deposits of Lake La- 
hontan consist of the bones of mammals and fishes ; the shells of fresh- 
water mollusks and of ostracoid crustaceans ; the larval cases of a caddis 
fly; a single chipped implement of human workmanship; and vegetable 
vestiges of a doubtful nature. 

Mammalian bones were obtained at a number of localities in the sides 
of the Humboldt and Walker River cafions, and, with the exception of a 
single vertebra found in the medial gravels, they were all derived from the 
upper lacustral beds. These fossils were submitted to Prof O. C. Marsh for 
determination, but only a partial report as to their character has been ren- 
dered. So far as determined they include a proboscidian (elephant or mas- 
todon), a horse, an ox, and a camel. The fossils were usually detached 
and scattered through the sediments, more than one or two bones of the 
same individual being seldom found at a single locality, except in the case 
of the elephant or mastodon bones obtained in the Humboldt Cailon near 
Rye Patch, where nearly an entire skeleton must have been entombed; 
many of the bones had been removed, however, before the locality was 
visited by the writer. The failure to obtain mammalian remains from the 
lower lacustral deposits is of but little weight as negative evidence, for the 
reason that the beds are imperfectly exposed ; a more critical search would, 
perhaps, reveal an abundance of fossils/® 

7^1 would fliiggost iu this connection that the disappearance of a number of large mammals firom 
the fauna of this continent since the deposition of the upper Lahontan sediments may have been 
caused by the extreme aridity which followed the last recession of t)ie lake. An intensely arid climate 

238 



FOSSIL FISHES. 239 

The remains of fishes were found at a few localities in the upper lacus 
tral clays exposed in the Truckee Cafion. No determination of these fossils 
has been made, farther than the fact that they belonged to Teleost fishes of 
considerable size. They probably indicate that the ancient lake was not 
strongly alkaline or saline, but, on the other hand, they are not proof that 
it was fresh ; as a number of the brackish lakes of the Great Basin at 
the present time are abundantly stocked with fish. Little weight can be 
attached to these fossils, however, in determining the character of the former 
lake, for the reason that tliey might have been contributed by inflowing 
streams even though the water of the lake was a strong brine. Dead fish 
are sometimes found floating in Great Salt Lake, Utah, which must have 
come from the inflowing streams. These are preserved for a long time by 
the brine of the lake but must eventually become buried in the sediments 
now forming at the bottom of the basin, and, when fossilized, will, in a cer- 
tain sense, form a false entry in the geological records. 

During our examination of the Lahontan basin, fossil shells were ob- 
tained at a large number of localities, and in many instances were found in 
great abundance. Both the fossil and recent mollusks collected, together 
with the similar material previously obtained by Mr. Gilbert from the Bon- 
neville basin, were studied by Mr. R. Ellsworth Call, who also paid a brief 
visit to each of the ancient lake basins during the summer of 1883, for the 
purpose of increasing the collections and making himself personally familiar 
with the peculiarities of the region. The results of Mr. Call's investiga- 
tions have been published as Bulletin No. 11 of the Reports of this Survey, 
to which the reader is referred for detailed information in reference to the 
fossil shells mentioned in the present volume. Besides the shells inclosed 
in tufas and lacustral sediments tliere are others, termed semi-fossil, which 

certainly followed the disappearance of the Quaternary lakes of the Far West, and, so far as that re- 
gion is concerned, this would furnish a sufficient cause for the extinction of the largo mauinials 
which were formerly abundant. This hypothesis is open to objections, however. Evidence that an 
arid climate succeeded the Glacial epoch in the eastern portion of this continent has not been recognized. 
Even if it could be shown that a period of extreme aridity preceded the present climat'C, it is difflcalt 
to understand why certain mammals, as the elephant, mastodon, horse, camel, megalonyx, etc., 
should have become extinct, w^hile others no more capable of withstanding gnat changes of environ- 
ment should have survived. The recent extinction of a number of mammals is an enigma the solu- 
tion of which would reflect much light on the mutations of faunas during the older and still more 
obscnre portions of geological history. 



240 



GEOLOGICAL HISTOBY OF LAKE LAHONTAN. 



frequently occur in abundance on the eui-faces of the deserts at a distance 
from existing streams and lakes Some of these unquestionably lived in the 
former lake during its last recession and were left strewn over its bottom 
when desiccation took place ; in many cases, however, the surface shells 
are true fossils that have been separated from their matrix of clay and marl 
and accumulated in certain areas by the action of the wind. Other "dead 
Bhells," of which Pyrgula Nevadensis is an example, have only been obtained 
about the shores of the existing lakes and are probably still living in theii' 
waters ; tliese are also termed semi-fosoil. 

The thousands of shells obtained are all of fresh-water forms, and 
include 27 species, grouped under 20 genera and 7 families. The genera 
and species, together with the horizon from which they were obtained, are 
indicated in the following table : 

Tabhof ehelU found iH the Lahonlan barim. 





!i 


n 

IB' 


tl 

+ 
+ 
+ 
+ 

4 
+ 

+ 


+ 
+ 

+ 
+ 

+ 
+ 

+ 
+ 




^ 
I 


u 


1 

+ 
+ 
+ 
+ 

+ 

+ 


A. 

+ 






' + 


huinm..9«J' 




.... 


J ' „ 1 






P™iplm1.yi;<>iru».,L«. 


+ 


+ 


+ 




i 




Aiic)luBNowlH.[Tji,Le» 




.... 


























I + 


+ 








+ 
+ 

+ 




















* 


V.lldnUpiilchplliHull 

Pupllln miuoonua, Linn 










LlmD»phyi»|m]iuM.iUu1l 


+ 


+ 


+ 




I 


* 


29 


w 







In arranging the fossils according to their geological horizons we have 
considered the lower lacustral beds as, at least in part, contemporaneous 
with the lithoid tufa ; the medial gravels have been correlated in time with 
the thinolitic tufa; and the upper lacustral clays with the dendritic tufa. 

As indicated in the list, only a single species {Pompholyx effusa) has 
thus far been derived from the lower lacustral clays. This was found in 
great abundance in the Hthoid tufa on Anaho Island, and was equally com- 



FOSSIL MOLLUSKS. 241 

mon in other localities at a corresponding geological horizon. This is the 
most abundant and characteristic fossil of the Lahontan sediments ; it occurs 
from the base of the oldest of the tufa deposits all the way through the 
series, and is one of three species of moUusks found living in Pyramid Lake 
at the present day. 

All the fossil shells obtained are of recent species, and the majority 
have been found living in the Great Basin. A comparison of the living and 
fossil forms has shown that the fossils are depauperate, and exhibit greater 
variations in the size, thickness and sculpture of their shells than occur in 
living examples of the various genera and species when obtained from 
regions where they find a congenial environment. In this connection Mr. 
Call says: 

''The wide range of Pompholyx in Lahontan beds makes possible a 
valuable comparison of the same species from localities representing stages of 

the lake widely separated in point of time Specimens taken from 

the lithoid tufa on Anaho Island, in Pyramid Lake, when compared with those 
from horizons correlated with the dendritic period present the widest range 
among individuals. The shells from both localities are higher than Pyra- 
mid Lake form, are much thinner, and the coiling of the whorls is much 
looser. The lithoid tufa specimens present a large proportion of costate 
forms, the ratio being as I to 2, while in recent specimens the ratio is as 1 
to 32. The recent species approximate P. effusa^ var. solida Dall, while in 
sculpture and elevation the earlier forms of the lithoid tufa approach nearest 
to the typical P. effusa^ Lea." 

Comparative measurements of Pompholyx effusa from deposits of lower 
and upper Lahontan beds, and of specimens found living in Pyramid Lake, 
show that the average size of the fossils from the older horizon is below that 
of the Pyramid Lake specimens; while those from the upper Lahontan sedi- 
ments are larger than the living examples. On comparing the size of the 
Pyramid Lake specimens with the average of the same species from fresh 
water localities in the same region, it was found that the shells from fresh 
water were larger than those obtained from Pyramid Lake, which, it will be 
remembered, is somewiiat saline and alkaline (see analyses, pages 57 and 58). 
A large number of measurements of fossil and living forms, shows that the 
Mon. XI 16 






u 



242 GEOLOGICAL UlSTORY OF LAKE LAHONTAN. 

Lahontan fossils are smaller and exhibit greater variation than the same 
species when living under normal conditions. On comparing the size of 
Ponipholjjx from Anaho Island (lower Lahontan), '* white terrace" (upper 
Lahontan), and White Pine, Nevada, (Hving), the ratio of 63 : 88: 100 was 
obtained." 

The investigations of conchologists have proven that there are al least 
three vjiriations of environment which may cause depauperation in fresh 
water mollusks, viz., salinity, low temperature, and scarcity of food. 

As regards salinity, it has been sliown that a sudden change from 
fresh to saline water, i. e., to water resembling that of the ocean, is fatal 
to fresh -water mollusks. When the change is gradual the life of the spe- 
cies may be niaintained until a considerable degree of salinity is reached, 
but the limit has not been determined, and is known to vary widely with 
difterent species. '1\) make the experiments in this direction definite and 
comparable with the gradual changes which t^ike place in the waters of 
inclosed lakes, would require a much greater length of time than has yet 
been devoted to the subject. Knougli has been determined, however, to 
show that a gradual increase in the salinity of a lake would be accompanied 
with the depauperation and decrease of its molluscan life; should the salinity 
continue to increase until a condition approximating that of the ocean was 
reached, the molluscan life would become nearly if not completely extinct. 
We may reasonably conclude, therefore, that the waters of Lake Lahontan 
were not strongly alkaline or saline during the time the sediments and 
tufas so richly charged with fossil shells were deposited. It is perhaps 
well to mention in this connection that there is no reason to doubt that the 
mollusks whose shells are found in such abundance actually inhabited the 
ancient lake. They could not have been contributed by inflowing streams 
and are not found in excei)tional abundance where springs entered the 
lake. The degree of salinity attained by the ancient lake cannot be deter- 
mined, but, as we have seen, must have been low, at least during the high- 
water stages. This conclusion is most definite in the case of the upper 
lacustral marls which ai*e frequently charged with the shells of Anodonta^ a 
genus which, at the present time, is confined to waters of exceptional purity. 

•' Tbeb(5 measure lueiitH ref«M- to tho luugtb of the sholls. 



ABSENCE OF MOLLUSKS IN SALINE LAKES. 243 

In the experiments that have been made in reference to the influence 
of saline waters on the life and growth of fresh water moUusks, the effect 
of common salt (sodium chloride) has principally been considered. The 
lakes of Nevada, however, are characterized by the presence of alkaline 
carbonates, which it is believed have a more decidedly deleterious effect on 
the life and growth of fresh water mollusks than common salt. This con- 
sideration lends still greater weight to the conclusion that the waters of the 
former lake were not highly charged with mineral matter during the time 
the fossil-bearing sediments and tufas were formed. 

The condition of several of the enclosed lakes of the Great Basin at 
the present time, however, indicates that a very moderate degree of salinity 
and alkalinity is perhaps favorable to the growth of fresh water mollusks. 
Franklin, Ruby and Humboldt lakes are all more highly charged with salts 
than is the case with ordinary lakes and streams (the total of solids in solu- 
tion, however, not exceeding a small fraction of 1 per cent.) but have an 
abundant moUuscan fauna. The inference is that a decided although indefi- 
nite degree of salinity is requisite to produce depauperation. In the more 
strongly saline and alkaline lakes, of which Mono, Abert and Great Salt 
Lake are examples, careful search has been made for living mollusks but 
none have been found. These lakes are believed to be entirelv destitute 
of both molluscan and piscine life. 

As Lake Lahontan never overflowed, it is safe to conclude that its 
waters at all times must have been less pure than those of ordinary lakes 
with outlet. The depauperation of its fossils and their variation in size at 
various horizons, are thus correlated with known saline and alkaline condi- 
tions, which also varied with fluctuations of lake level. We conclude, 
therefore, that at least one cause of the depauperation of the mollusks now 
found fossil was the chemical composition of the waters they inhabited. 

In reference to the evidence furnished by the Lahontan fossils as to 
the climate of the Quaternary, a conclusion seems impossible at this stage 
of the investigation, for the reason that a suflBcient cause for the observed 
variation and depauperation of the shells has been found in the chemical 
character of the waters in which they lived. If we postulate a cold Quater- 
nary climate, the logical sequence would be a depauperation of the fresh- 



244 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

water moUusks; but since a similar change would result from the necessary 
chemical condition of the waters of an inclosed lake in which concentration 
had been long continued, no definite conclusion as to the eflFect of the low 
temperature seems possible. On the other hand, a warm Quaternary cli- 
mate would presumably be favorable to the growth of mollusks, but even 
if the climatic conditions were favorable, a more potent element in their 
environment caused the shells to become depauperate. 

Mr. Call's studies have shown that the raolluscan fauna of Lake La- 
hontan was characterized by the predominance of the lAmnoeidce. This 
family of mollusks at the present time is of world-wide distribution, but is 
found most abundantly in cold-temperate and subarctic regions. During 
the Quaternary it may be presumed to have had a similar isothermal distri- 
bution. Thus in a very general way it might be inferred that the Quater- 
nary climate in the region of Lake Lahontan was colder than at present 
The wide distribution of the LimncBidcej however, and their known powers 
of enduring marked changes of environment, render this conclusion of 
doubtful value. The majority of the moUuscan species that inhabited Lake 
Lahontan are still living in the Great Basin, and so far as this branch of 
the palseontological evidence bears witness, we see no reason for conclud- 
ing that the former climatic conditions differed materially from the present. 
The only safe inference seems to be that the climate of the Great Basin 
during the life of the mollusks we are considering was not characterized in 
mean temperature by extremes of either heat or cold. 

As regards the scarcity of food in Lake Lahontan, in reference to the 
depauperation of its moUuscan fauna, we know that the mollusks now found 
fossil, like their living representatives, must have subsisted mainly on con- 
vervoid growths. This form of vegetable life flourishes not only in fresh, 
but also in brackish and alkaline waters, as may be seen in the various 
lakes of the Great Basin at the present time. There is therefore no reason 
to conclude from the probable composition of the waters of Lake Lahontan 
that food of the character required by mollusks was not abundant. The 
profusion of fos il shells in the sediments and tufas leads to the same con- 
clusion, for without sufficient food moUuscan life could not have been so 
prolific. 



i 



SEMIFOSSIL SHELLS. 245 

The fossils that might be expected to throw the most light on the cli- 
matic problem are the mammalian remains, but, unfortunately, up to the 
present time these have been found in such limited numbers that but little 
evidence as to the nature of former climatic changes can be derived from 
them. 

Throughout Lahontan history Pompholyx effusa was the most abundant 
species in the moUuscan fauna, but only a very few individuals of this genus 
have been found living in the present lakes of the basin. Moreover, the 
dead shells of Pyrgula Nevadensis occur in profusion on the shores of Pyramid 
and Walker lakes, but have not been discovered among Lahontan fossils. 
This species is probably now living in the lakes of the region, as is indi- 
cated by the fresh appearance of the shells, in some of which the soft parts 
of the mollusks are still adhering. 

The occurrence of Pompholyx throughout the Lahontan series and its 
rarity in the existing lakes of the basin, as well as the absence of Pyrgula 
from Lahontan fossils, and its abundance in a semi-fossil condition, are be- 
lieved to indicate that there was an inkrregnum between the time of Lake 
Lahontan and the beginning of the present lakes of the basin. If our read- 
ing of the records is correct, this time of change was a period of extreme 
desiccation during which the lakes of the region evaporated to dryness, their 
salts becoming buried beneath playa deposits, and their molluscan life nearly 
if not completely exterminated. 

The absence of Pyrgula in Lahontan sediments, and its abundance in a 
semi-fossil condition about the shores of the present lakes, in which it is 
now rare, seems explicable on the assumption that it was introduced into 
the basin at a recent date and found a congenial habitat in the mildly saline 
waters of Pyramid and Walker lakes. Subsequently these lakes became 
too saHne and alkaline for its existence, and it was nearly if not completely 
exterminated, so far as they are concerned. The present chemical compo- 
sition of the lakes in question is believed to indicate about the limit of 
salinity or alkalinity that fresh- water mollusks can sustain. 

The cases of a minute crustacean of the genus Cypris occur through- 
out the Lahontan series, and at times are so abundant that they form the 
principal portion of strata for several feet in thickness, as may be seen in 



246 GEOLOGICAL HISTORY OP LAKE LAHONTAX. 

the walla of the Truckee Canon. At the base of the layer of dendritic tufa 
exposed along the Humboldt and Trnckee rivers this fossil occurs in-pro- 
fusion, frequently intermingled with the shells of Pomj)hoIyx. On the bor- 
ders of the Carson Desert the cases of Cypris have been accumulated by 
the wind in such quantities as to form small drifts resembling sand dunes. 
What specific name this fossil may bear has not been determined, but spe- 
cies with which it is evidently closely rehited are known to live in both fresh 
and salt water. Its value, therefore, as indicating the nature of its environ- 
ment in Lake Lahontan is indefinite. 




Fin. Jl.— Larval 



At a single locality, the larval cases of a caddis fly were obtained, 
which were coated over and partially imbedded in lithoid tufa (Fig. 32). 
This fossil is very similar to the larval cases of the caddis fly now found 
abundantly in streams and lakes, and, so far as the evidence goes, indicates 
that the waters in which the fossils were formed were not intensely alkaline 
or saline. 

The worm-like larval cases of a fly occur in tlie tufa about the Soda 
Lakes near Ragtown, but these are evidently of quite recent date and cannot 
be considered as Lahontan fossils. 

The fossil from the Lahontan basin that will probably be considered 
by both geologists and arcliEcologists as of the greatest interest, is a spear- 



r 



MAX IN TDE QUATERNARY. 247 

head of human workmanship. This was obtained hy Mr. McGec, from the 
upper lacnstral clays exposed in tlie walls of Walker River Canon, and was 
associated in such a manner with the bones of an elephant, nr mantodon, as 
to leave no doubt as to their having been buried at approximately the same 
time. Both are genuine fossils of tiie upper Lahontan period. The spear- 
head is of chipped obsidian and Is in all respects similar to many other 
implements of the same nature found, commonly on the surface, through- 
out the Far West. It was discovered projecting point outwards from a ver- 
tical scarp of lacnstral clays 25 feet below the top of the section, at a local- 
ity where there were no signs nf recent disturbance. This fossil, which is 
the only evidence at present known of the existence of man on the shores 
of the Quaternary lakes of the Groat Basin, is represented natural size in 
the following figure. 




uf ubaliliaarroiD Lahnntan Brilimenti. 

The only fossils of a vegetable nature thus far referred to Lake Lahon- 
tan are certain problematic, stemlike tubes, from one to two inches in 
length, and approximately the thirtieth of an inch in diameter, which 
occur in great profusion at the base of the hthoid tufa on Anaho Island. In 
some places the lower two or three feet of the tufa is very largely com- 
posed of these remains. Our reference of these fossils to the vegetalde 
kingdom is only jirovisional, however, as they have been examined by 
several skilled pala-ontologists without having their relations definitely deter- 
mined. It has been suggested that they are the ciists of grass-like stems, 
but their uniform diameter and the absence of joints seems to preclude 
this determination. In describing the variations presented by T'onqihtdi/x 
from Anaho Island, Mr. W. II. Dall lia.s siwkcn of these fossils as the ca-sts 
of the leaves or needles of the pine;'* it is possible that this may bo the 
true explanation of the enigma. 

■-Si-iiTn-i'. Vol. ]. l-'ri:), )., 'Mi. 



248 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

No leaves or vegetable stems of any kind, excepting the fossils men- 
tioned in the last paragraph, have been found among the records of the old 
lake, and no drift timbers seem to have been deposited in the bars and 
embankments that have been examined. The absence of such fossils appar- 
ently indicates that the shores of the former lake were not heavily wooded. 
The borders of our Northern lake^i at, the presejit day are thickly clothed 
with forests and their shores encumbered with stranded logs and stumps in 
such quantities as to have considerable influence on the character of the 
shore phenomena resulting from wave action. Had the shores of Lake 
Lahontan been as densely wooded as are those of Lake Michigan, for 
example, it seems impossible that abundant records of the fact should not 
have been discovered during our sojourn in the basin. 

A superficial microscopical examination of the sediments of the ancient 
lake has shown that they are richly charged with the silicious skeletons of 
infusoria, and sometimes abound in sponge spiculse. A detailed study of 
these fossils was not practicable, and, as these forms of life are so widely 
distributed and live under such diverse conditions, it seems doubtful in the 
present instance, if a more critical examination would greatly assist in solv- 
ing the chemical and climatic problems with which the student of the Qua- 
ternary geology of the Great Basin is principally concerned. 

No fossils have been found in the thinolitic tufa, although careful search 
has been made at many localities. At times shells may be seen in the open 
spaces between the crystals, but these are believed in all cases to have been 
accidentally introduced at a recent date. The absence of all life records 
in this deposit strengthens the hypothesis that the thinolite was crystallized 
from waters highly charged with mineral matter. 

In correlating the various Lahontan deposits we have considered the 
thinolite as stratigraphically intermediate between the lower and upper 
lacustral clays, and, at least in part, contemporaneous with the medial 
gravels. The fossils obtained from the medial gravels are of fresh-water 
species, but were collected near the borders of the basin and at a greater 
elevation than the upper limit of the thinolite. The fossils may thus rep- 
resent a stage in the recession or in the refilling of the lake when its waters 
were not so dense as when the thinolite was crystallized. In the Humboldt 



SUMMARY OF PAL^ONTOLOGICAL EVIDENCE. 249 

Gallon where fossils were found in the medial gravels, it is probable that the 
strata are in part a flood plain deposit, accumulated when the lake was 
below that horizon. 

SUMMARY, 

The evidence derived from organic remains indicates that Lake 
Lahontan throughout its higher stages was never a strong saline and 
alkaline solution. Even during the abundant precipitation of dendritic tufa 
the lake was inhabited by moUusks in great numbers, and was probably 
also the home of Teleost fishes of large size. During the thinolitic stage, 
when its waters were greatly concentrated by evaporation, the absence of 
fossils indicates that it was uninliabited by either fishes or mollusks. 

The life history of the lake, as we know it at present, caimot be con- 
sidered as aifording definite information in reference to the character of the 
climate during the Quaternary. The reason is that any change in the 
molluscan life that might be due to climatic oscillations, is complicated and 
masked by the effects produced by variations in the chemical composition 
of the waters. 

When other basins in the same region are explored, especially those 
which found outlet, the character of their moUusean fossils may lead to 
positive conclusions in this direction, for in such instances the influence of 
an abnormal chemical condition of the waters on the growth of mollusks 
would be eliminated. 



CHAPTER VII. 

RfiSUMfi OF THE HISTORY OF LAKE LAHONTAN. 

The history of the fluctuations of the Quaternary lake of northwestern 
Nevada is recorded in various ways, as has been described in the last three 
chapters, which treat it from the physical, chemical, and biological stand- 
points; in the present chapter it is our pui*pose to present briefly the con- 
clusions based upon these various lines of evidence. The phenomena 
observed have great diversity of character, but when interpreted in terms of 
geological history, they support and supplement each other in such a way 
that the conclusions drawn are believed to be well sustained. Moreover, 
the facts observed in the Bonneville basin and in more than a score of desert 
valleys throughout the northern half of the Great Basin which contained 
contemporary water-bodies, harmonize with the interpretation of the I^a- 
hontan record here presented. 

The fact that all the minor basins in the arid regions of the Far West 
are filled to a depth of many hundreds of feet with alluvium and lacustral 
sediments, together with the occurrence of the beach lines of the Quaternary 
lakes on the surface of the vast alluvial cones, leads to the conclusion that 
all these basins were barren deserts before the rise of the Quaternary lakes. 
The pre-Lahontan condition of northwestern Nevada must have closely 
resembled its present character, but at times it was probably completely 
desiccated. 

The change of climate admitting of the existence and gradual expan- 
sion of lakes in the various valleys throughout the Great Basin caused a 
number of those situated in northwestern Nevada to rise suflBciently to unite 
and form a single irregular water-body 8,922 square miles in area. This 

250 



RfiSUMfi. 251 

was the first rise of Lake Lahontan. Like all inclosed lakes it must have 
fluctuated in depth and extent with the alternation of arid and humid seasons, 
and risen and subsided also in response to more general climatic oscillations, 
which extended through years and perhaps embraced centuries. Finally 
the climatic conditions which favored lake expansion ceased, and a time of 
aridity, like that which preceded the first rise, was initiated. The lake 
slowly contracted until its basin reached a greater degree of desiccation 
than that now prevailing. This was the inter-Lahontan period of desiccation. 

During the first rise lacustral marls and clays were deposited through- 
out the basin; the depth of these is unknown, but they certainly exceed 
150 feet in thickness. The waters were saturated with calcium carbonate 
and the precipitation of great quantities of compact stony tufa took place. 
Deposits of tufa were formed on rocky slopes throughout the basin, and 
are not especially abundant at the mouths of streams. This is thought to 
indicate that although the waters were saturated with calcium carbonate, 
they were not highly charged with other chemical substances. This con- 
clusion is sustained by observation of conditions under which a similar tufa 
is being deposited in existing lakes, and also by the presence of gasteropod 
shells in the lithoid tufa in great abundance. 

The time of low water, and perhaps of complete desiccation, that suc- 
ceeded the first rise of Lake Lahontan, is recorded by stream channels 
carved in the lacustral beds and by current-bedded gravels and sands super- 
imposed upon previously formed strata. Sections of inter-Lahontan gravel 
deposits have been observed wherever the material filling the lake basin is 
well exposed, and furnish indisputable evidence that the lake was greatly 
lowered before the gravels were deposited. These gravels were in turn 
covered by a second lacustral deposit, thus forming a tripaitite series, a 
counterpart of which exists in the Bonneville basin. The first formed tufa 
deposit was exposed to subaerial erosion during the inter-Lahontan period 
of low water and became broken and defaced. 

The character of the next succeeding tufa deposit indicates that a 
change had taken place in the chemical conditions of the waters of the lake 
when the basin was again partially flooded. This alteration in the com- 
position of the salts dissolved in the lake is thought to have been brought 



I I 

1 I 



I ' 

t 



■ I 

l! 



252 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

about by a partial deposition of the saline matter accumulated during the 
first high- water stage, at the time of the inter-Lahontan period of desiccation. 
The tufa superimposed upon the lithoid variety is known as thinolite; it is 
composed of well-defined crystals and is without fossils. It was evidently 
precipitated from a more highly concentrated chemical solution than that 
from which the lithoid variety was deposited. That this was the case is 
rendered evident, since the crystalline variety occurs only low down in the 
basin, while the lithoid tufa may be found within 30 feet of the highest 
terrace carved by the waters of the ancient lake. 

After the crystallization of thinolite had been carried on for an indefi- 
nite period, the lake rose to within 180 feet of its first maximum, and the 
heaviest deposit of calcium carbonate found in the basin was precipitated* 
During this stage the lake was not strongly saline, as is shown by the abund- 
ance of gasteropod shells obtained from the sediments and tufas accumulated 
during this portion of its history. 

After the precipitation of the dendritic tufa, the lake continued to 
rise and at last reached a horizon 30 feet higher than the first maximum. 
During this expansion the waters lingered but a comparatively brief time at 
the highest level and then slowly subsided. The increase in depth after the 
deposition of dendritic tufa is shown by the presence of lacustral sediments 
I upon that deposit. The structure of the higher bars and embankments 

about the border of the old lake basin, proves conclusively that the greatest 
lake expansion was during the second rise. 

With the last recession of the lake all portions of its basin were brought 
within the teach of wave action, and the tufa deposits sheathing its interior 
were broken, and the fragments swept away by currents, and built into em- 
bankments and terraces. The waters continued to fall until the basin was 
completely dry. All the salts not previously precipitated were deposited 
as desiccation advanced, and became buried and absorbed by playa clays. 
1/ The proof of the occurrence of this time of desiccation is furnished by the 

comparatively fresh condition of the existing lakes of the basin, and by the 
change in the moUuscan fauna which took place since the last high-water 
period. The duration of this post-Lahontan arid period is unknown, but 



y 



RfisuMfi. 253 

it was finally terminated — probably less than 300 years since — by an in- 
crease in humidity. The present lakes then commenced their existence. 

Throughout its history, Lake Lahontan has been subject to a multi- 
tude of minor oscillations, as is indicated by the banded and stratified char- 
acter of the tufa deposits lining the interior of its basin. 

The character of the climatic changes which brought about both the 
great expansions and contractions of Lake Lahontan, as well as the minor 
fluctuations to which it was subject, will be indicated, so far as the writer 
has been able to interpret the records, in the following chapter. 



CHAPTER VIII. 

QUATERNARY CLIMATE. 

In preceding chapters we have considered the physical, chemical, and 
biological histories of Lake Lahontan, as determined from facts gleaned 
here and there in its now empty basin. In each of these chapters reference 
has been made to the climatic conditions on which these various elements 
of history depended. In the present chapter it will be our aim to review 
the evidence afforded by the records of the ancient lake which have a bear- 
ing on the determination of the climatic conditions that permitted of its 
existence. 

The investigations of naturalists have shown that the fauna and flora 
of a region are expressions of its climatic condition. To the geologist, the 
physiography of a country reflects, with nearly equal clearness, the effects 
of that resultant of a plexus of independent meteoric forces, designated by 
the term climate. Each year, as the seasons succeed each other, the geo- 
logical changes, that are ever active, although so slowly and so silently 
that many times they escape observation, may be correlated with the ele- 
ments of climate on which they are most closely dependent. Of the atmos- 
pheric forces at work, on every hand, in remodeling the earth's surface, 
those dependent upon humidity and temperature are the most obvious. 
These vary in intensity with the seasons, and at times their independent 
workings may be observed. Throughout the geological ages these same 
invisible agents of the air have never ceased to work changes on the earth, 
at times surrounding it with warmth, beauty, and life, and again, as the 
aeons passed on, blotting out the fair picture themselves had drawn, and 
replacing it with cold, desolation, and death. 

The general effects of climate are so well known that one may predict 
the results produced by its various elements on the aspect of a given region. 

254 



TOPOGRAPHY OF ARID REGIONS. 255 

The geologist is enabled to reverse this process, with greater or less success, 
and, from the records in the rocks, determine the prevailing climatic condi- 
tions of bygone ages. The interjM-etation of the Lahontan records in terms 
of climate is at the same time the most interesting. and the most diflficult of 
the problems that their study lias suggested. The character of the Quater- 
nary climate of the Great Basin has been treated in a comprehensive manner 
by Mr. Gilbert in a monograph on Lake Bonneville, which, it is expected, 
will soon be published. We are thus, not unwillingly, constrained to con- 
fine our studies to the evidence afibrded by the records of Lake Lahon- 
tan. Our attention will necessarily be mainly directed to the questions of 
humidity and of temperature. 

Among the topographic characteristics of arid regions are angular 
mountain tops, canons with precipitous walls, and alluvial cones where 
streams from the mountains lose their grade upon reaching the valleys. 
The last of these features is perhaps as striking as an} of the others, and 
is of special interest in the present discussion. Many times the bases of 
mountains are completely encircled by a sloping pediment of unassorted 
debris, either angular or rounded, which is the most abundant at the mouths 
of canons. Such accumulations form alluvial slopes, and when the debris 
occurs in more or less conical or fan-shaped piles it forms alluvial cones. 
These deposits have been studied especially by Drew''® and Gilbert;^ by 
the former in the arid regions of Southern Asia, by the latter in the Great 
Basin. As described by Gilbert, **The sculpture of a mountain by rain is 
a twofold process — on the one hand destructive, on the other constructive. 
The upper parts are eaten away in gorges and amphitheaters until the 
intervening remnants are reduced to sharp-edged spurs and crests, and all 
the detritus thus produced is swept outward and downward by the flowing 
waters and deposited beyond the mouths of the mountain gorges. A large 
share of it remains at the foot of the mountain mass, being built into a 
smooth sloping pediment. If the outward flow of water were equal in all 
directions this pediment would be uniform upon all sides, but there is a 
principle of concentration involved, whereby rill joins with rill, creek with 

T* Journal Geological Society of London, Vol. XXIX, 1873, i>p. 441-471. 
» Second Annual Report U. S. CJeological Survey, p. 183 et seq. 



I I 



• 



t' 



■1 

I 



256 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



creek, and gorge with gorge, so that then when the water leaves the margin 
of the rocky mass it is always united into a comparatively small number 
of streams, and it is by these that the entire volume of detritus is discharged. 
About the mouth of each gorge a symmetric heap of alluvium is produced, 
a conical mass, of low slope, descending equally in all directions from the 
point of issue, and the base of each mountain exhibits a series of such allu- 
vial cones, each with its apex at the mouth of a gorge, and with its broad 
base resting upon the adjacent plain or valley. Rarely these cones stand 
so far apart as to be completely individual and distinct, but usually the 
parent gorges are so thickly set along the mountain front that the cones are 
more or less united, and give to the contours of the mountain base a scal- 
loped outline." 

In the Lahontan basin alluvial cones are to be seen everywhere about 
the bases of the mountains, and were evidently a conspicuous feature in 
the pre-Lahontan topography, as is abundantly illustrated by the fact that 
the shore lines of the former lake are traceable for hundreds of miles on 
alluvial slopes of great magnitude. This is particularly noticeable in the 
northern portion of the basin where the lake was generally shallow, and 
may be observed especially in the Humboldt and Quinn River valleys and 
about the bases of the Slumbering Hills. The same phenomenon is also 
conspicuous about the borders of the Carson Desert and in Buffalo Spring, 
Alkali and Mason valleys, as well as at many places on the borders of 
Walker Lake Valley. These alluvial slopes streaming down from the 
mountains to a horizon far below the old beach lines, bear evidence that 
the valleys were deeply filled with alluvium before they were occupied by 
the Quaternary lake. Since many of these basins never overflowed, it is 
evident that the alluvial slopes were formed during a time of desiccation 
when evaporation equaled or exceeded precipitation. If this had not been 
the case, it is manifest that lakes would have been formed and the debris 
filling their basins arranged in stratified beds or built into bars and em- 
bankments. A large number of valleys in the northern part of the Great 
Basin which held inclosed Quaternary lakes have been explored, and in 
each instance the same relation of shore terraces to previously formed 
alluvial slopes has been observed. It is therefore considered as proven 



i! 



subaBrial alluviation. 257 

that an arid climate prevailed for a long time previous to the existence of 
the Quaternary lakes, the records of which are now observable. The rate 
at which alluvial cones are formed is irregular and depends on a number 
of variable factors, as, for example, the amount of precipitation, the grade 
of the cailons, character of the rock forming the mountain, etc. As the 
geological and topographical conditions at a definite locality may be con- 
sidered constant, so far as the present discussion is concerned, it is evident 
that alluvial cones are in some manner a record of rainfall. Many obser- 
vations have shown that they are usually formed in arid regions, and result 
from sudden storms which flush. the canons and sweep out the accumulated 
debris with violence. This is observable not only during the occasional 
"cloud bursts," as the sudden storms of the Far West are called, but may 
also be inferred from the occuiTcnce of angular rocks, weighing many tons, 
on the surfaces of the alluvial cones. During the intervals between the 
storms, disintegration takes j)lace in the uplands, and the smaller tributaries 
deposit their loads in the larger cailons, whicli thus become charged with 
debris. The rapid deposition of alluvium about the mouths of cailons is 
largely influenced by the fact that what was entirely a surface stream 
during its caOon course, sinks below the surface on passing to the alluvial 
slope and deposits its load. These considerations might be extended and 
the action of perennial streams contrasted with the results produced by 
infrequent stonns, but perhaps enough has already been written to show 
that alluvial cones are not only characteristic of arid climates but that the 
precipitation which produced them is commonly paroxysmal. There is mani- 
festly no uniform rate at which subaerial alluviation takes place and no 
definite measure of the time necessary for the accumulation of debris of 
this character, but the comparative size of the deposits made during distinct 
periods furnishes at least a general indication of the relative length of time 
required for their accumulation 

Assuming that the conditions of allaviation were equally favorable 
during the pre-Lahontan and recent arid })eriods, we may determine from 
the magnitude of the subaerial deposits in each instance the relative dura- 
tion of the two periods. The Lahontan terraces carved on the slopes of 
ancient alluvial cones are but delicate inscriptions which, in a geological 
MoN. XI 17 



' .1 



' 



tl 
n 
i' 

;i 



t 

■ • 



J 



I 



258 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

sense, are extremely ephemeral, yet they are clearly legible at the present 
day, thus indicating the recency of their origin. The time that the terraces 
have been exposed to subaerial erosion must evidently be extremely brief 
in comparison to the ages required for the accumulation of the vast debris 
piles on which they were made. 

Another, although less definite proof of the aridity of the time preced- 
ing the rise of Lake Lahontan is furnished by the caiions of the streams 
that enter the basin. In many instances these were excavated to their 
present depth before the existence of the lake, which subsequently occupied 
their channels for many miles. An illustration of this phenomenon is fur- 
nished by the cafions of Smoke and BuflFalo creeks, which were eroded to 
the depth of 250 or 300 feet through compact basalt before the rise of Lake 
Lahontan. When the lake had its greatest extension it occupied the lower 
portions of these gorges and filled them deeply with marly-clays and delta 
deposits, at the same time that their walls became loaded with tufa. When 
the lake retired the streams reclaimed their ancient channels and com- 
menced the removal of the lacustral strata. The creeks are now flowing 
over their ancient beds of basalt, but the recent corrasion of the volcanic 
rock is scarcely perceptible. The amount by which the caiions have been 
deepened during the present arid period, as compared with the work accom- 
plished in pre- Lahontan times, is certainly in the proportion of one to many 
thousand. Parallel illustrations of the same phenomena are furnished by 
the rivers which enter the basin from the west, all of which flow in channels 
of pre-Lahontan date, and became partially filled with lacustrine strata and 
subsequently re-excavated as in the previous instances. Each of these 
streams now flows through a caflon within a caflon, in the manner illus- 
trated by the diagram on page 44. 

It might be said that when these cations were formed, the basin to 
which they are now tributary had a free drainage to the sea. It is impos- 
sible to prove or disprove this * hypothesis, but in general, caiions of the 
character of those in question may be considered as characteristic of arid 
regions. Besides, we know, from the great depth of marl and gravel in 
many of the valleys of the Great Basin, that they have been regions of 
accumulation for long periods. The weight of evidence is such, in our 



HUMIDITY OF THE QUATERNARY. 259 

judgment, as to confirm the hypothesis that an arid period of long dura- 
tion preceded the first rise of Lake Lahontan of which we have definite 
knowledge. 

The variations and fluctuations of the pre- Lahontan arid period are 
unknown, but, from the general teachings of meteorology, we may reason- 
ably conclude that, like the present climate of the Great Basin, it was 
marked by many fluctuations in precipitation and evaporation, which at 
times gave origin to lakes of greater or less extent. As the arid period 
drew to a close and more humid conditions prevailed, it is most reasonable 
to suppose that the change was gradual. The phenomena do not call for a 
sudden break in the processes of nature. 

Humidity of the Lahontan period. — Inclosed lakes may be considered as 
representing the net balance between precipitation and evaporation. As 
the relations of these two climatic elements are complex and independent, 
their resultant will be inconstant and variable; their mutual neutralization! 
so far as the lakes of a region are concerned, must, therefore, be a matter 
of delicate adjustment. It follows from this that the diiference in climate 
between a time of expanded lakes and a time of desiccation might be com- 
paratively moderate. 

In a given area, like the Great Basin, we may safely say that a lower- 
ing of the mean annual temperature will increase precipitation and decrease 
evaporation, thus affording the climatic conditions favorable to the expan- 
sion of the lakes. On the other hand, a rise in the mean annual tempera- 
ture would increase evaporation and decrease precipitation, thus favoring 
the contraction and extinction of inclosed lakes. The existence of a large 
number of lakes in the Great Basin during the Quaternary is seemingly 
good evidence that the climate of the region during the time of their greater 
expansion was more humid than at present; unless it can be shown that 
there was a very great decrease of evaporation without a corresponding 
increase of precipitation, a phenomenon only to be observed at the present 
time in the arctic latitudes. 

That many of the lakes did not overflow is equally positive evidence 
that precipitation within their hydrographic basins could not have been 
excessive. Had the rainfall been even moderately copious, it seems self- 



I 

1 



.1) 

I 



li 



■i! 



li 



\ 
■I 



260 



GEOLOGICAL HIJSTOUY OF LAKE LAHONTAN. 



evident tliat the entire Great Basin must have become tributary to the 
ocean. Inclosed hikes of the present time are located in arid regions. 
The lakes of humid regions invariably overflow. In arid countries the 
water surfaces of tlie hikes are small in comparison to the areas that they 
drain; in humid regions the reverse is the rule. Lake Lahontan, as previ- 
ously stated, was 8,422 scpiare miles in area, and drained a region over 
40,000 square miles in extent; the water surface of the basin at tlie pres- 
ent time is approximately 1,500 s(|uare miles. The Quaternary lake dur- 
ing its maximum, occupied approximately one-fifth of its hydographic 
basin; at the present time only about one-twenty-sixth of the same area is 
covered by watei*. From these data alone it will be seen that the present 
is a time of desiccati(m in (M)m})arison tocertiiin portions of the Qllaterna^3^ 
Comparing Lake Lahontan with existing lakes in humid regions, we 
find that its water surface was small in reference to its drainage area. In 
the case of Lake Superior, for example, the area of the lake is to the area 
of its hydrographic basin as 1 to 1.72. llie combined areas of the Lau- 
rentian lakes is to their combined drainage areas as 1 to 3.19.*^ Could the 
Laurentian lakes be inclosed, so that the only esca})e for their waters 
would be by evaporation, it is evident that they would expand and occupy 
a vastly larger part of their drainage areas than at present. In fact, the 
mean annual evaporation in this region is much less than the mean annual 
rainfall, so that an inclosed lake would be an impossibility/" 

''•In obtuiuin^ thi) data given above, the following table was compiled, wbieb weinHert for conven- 
ience of reference. 

Areas of Jakea and of their lufdrograpliU' haniua. 



Lakeo. 



Suju'rior 

Micbi^un (inrludint; (Ireon Hay) 

Ilurou (incliKlin^ Northwest PasMUgo 1,550, 

and (j«or«yan Hay r»,02G) 

Saiut Clair 



Kiie 

Ontario 

Combined areas 

Bonnovillo 



W,.U.,- area.. n.v<l;;-«".,...i.- : ^^.f^^^ 
\ '"*^'^- graphic area. 



Square miles. 
30, 8iy 
21,729 :. 


«S'7 <tarr miles. 
SI, IKJl 


1 t4» 1.72 


1 

1 

•!■> 04>«> ] 

""" " 1 

390 . 
0, »i33 
7.104 
















9{.7:!:< i 


•JIK), 919 


1 to 3. 19 


19. 7r>u 


.'.J, OlMj 


1 to 2. 63 



^-Anu. Uei). Cbief of Engineers, V. S. A., l^r/J, pp. ()lo-()4«. 



HUMIDITY OF THE QUATERNAKY. 



261 



Considerations of this character might be multiphed, but it is presumed 
that enough has ah'eady heen written to show that the cUmatic change 
which gave origin to Lake Lahontan but did not permit it to overflow, must 
have been one of moderate precipitation in comparison, for example, with 
the present rainfall of the region of the Laurentian lakes, even if wo consider 
the rate of evaporation in the Great Basin to have been the same during 
the Quaternary as now. An increase in the annual rainfall of a region may 
safely be considered as causing a decrease in the mean evaporation, thus 
indicating that the rainfall in the region of Lake Lahontan during the Qua- 
ternary, could not have ])een greatly in excess of the present mean annual 
precipitation in the same area. It will be seen from this that the his- 
tory of Lake Lahontan is decidedly in opposition to the hypothesis that 
the climate of the Glacial epoch was characterized by a marked increase 
in precipitation. 

A safe conclusion seems to be that the change from arid to more humid 
conditions which produced the Quaternary lakes of the Great Basin was not 
sudden or excessive, but consisted in gradual climatic oscillations of moder- 
ate range. 

Considering the question of humidity alone, we venture to correlate 
periods of lake expansion with an increase in mean annual precipitation; 
and periods of contraction and desiccation with decrease of rainfall We 
therefore use the diagram representing the fluctuations of Lake Lahontan, 
as an expression of the humidity element in the climate of the region during 
the Quaternary. Interpreting the curve representing the oscillations of the 
lake in terms of humiditv we have: 




Fio. 34. — Carve of Labontan climate. Wet V€ravta dry. 



262 GEOLOGICAL HISTORY OP LAKE LAHONTAN. 

Temperature of the Lahontan Period. — Considering temperature as the 
controlling climatic element — in reference to a restricted region, as in the 
preceding discussion — and knowing that a high temperature promotes evap- 
oration and hence tends to decrease the volume of lakes, and that a low 
temperature produces a contrary result, we should apparently be justified in 
concluding that as the Quaternary lakes of the Great Basin were larger than 
the present water-bodies of the same region, the former climate must have 
been colder than the present. It may be said, however, that had the cold 
been intense and produced arctic conditions, precipitation would have been 
retarded. This postulate, however, is not applicable to the area in question, 
where the climatic oscillations were of moderate intensity even in compari- 
son with the present prevailing arid conditions, thus indicating that if the 
periods of desiccation were times of arctic cold, the lake periods must have 
been at least sub-arctic. On this assumption the Great Basin to-day should 
have a climate resembling that of circurapolar lands. The absence of " ice 
walls " about the smaller of the Quaternary lakes of the Far West is nega- 
tive evidence, perhaps of some value, in opposition to the above hypothesis. 
Moreover, the character of the abundant molluscan fauna of the Lahontan 
basin precludes the hypothesis of an arctic climate. 

If we postulate sub-tropical or tropical conditions of the Lahontan ba- 
sin during the Quaternary, we must, from the analogy of tropical countries 
in general, conclude that the region would probably have been humid as 
well as warm, and consequently productive of abundant faunas and floras. 
The absence of fossils indicative of such conditions is sufficient evidence 
that they did not prevail. In the chapter devoted to the life history of the 
former lake it has been shown that its shores must have been at least as 
desolate and lifeless as the borders of the existing lakes of the same region. 

The alternation of humid and arid conditions during the Quaternary 
finds, perhaps, its best analogue in the present annual climatic changes of 
the same region. The seasons in the Great Basin are two, an arid and a 
humid, the former being of the greater length. In the winter precipitation 
is abundant in comparison with the summer; in fact nearly the entire rain- 
fall of the year takes place between December and March. During these 
months the skies are clouded, and rain and snow are not infrequent ; the 



TEMPERATURE OF THE QUATERNARY. 



263 



rivers rise, and many channels that are completely dry during the summer 
become flooded ; tlie inclosed lakes increase in area and many new ones are 
formed in basins that are parched deserts during the summer months. The 
winter season is, therefore, the humid period, during which evaporation is 
decreased, and is in every way favorable to the existence of lakes. Could 
these conditions be continued for a sufficient length of time each year it is 
evident that the Quaternary lake basin would be refilled. 

On the other hand, throughout the arid season the rain ceases almost 
entirely, the skies are clear and cloudless for days and perhaps weeks at a 
time ; the heat in the desert valleys becomes intense, and evaporation is 
greatly accelerated. The result is a decrease and failure of the streams and 
the shrinkage and disappearance of the lakes. These annual changes illus- 
trate tlie character of the secular oscillations that took place during the 
Quaternary. 

The former great extension of the lakes of the Great Basin is, there- 
fore, considered as evidence that the mean annual temperature was then 
lower than at present. Interj^reting the curve given on page 237, which 
indicates the fluctuations of the Lake Lahontan, in terms of temperature we 
have the following as a generalized diagram of this element in the climate 
of the Quaternary: 




Fio. 85.— Gnrre of Lahontan climate. Gold vemu warm. 



In the last few pages of this attempt to decipher the prevailing char- 
acteristics of tlie climate of the Quaternary in the region of Lake Lahontan, 
the questions of humidity and temperature liave been considered in refer- 
ence to a restricted area. In treating of sucli a complicated and far-reaching 
question, however, it is evident that we should not be confined by gi^ograph- 
ical limits, but must count the changes of climate in broad and perhaps far- 



I 



264 GEOLOGICAL HISTORY OF LAKE LAHONTAK 



^1 distant regions. In fact, a study of the climate of a given region, to be 

complete, must contemplate the atmosplieric phenomena of the world. Nei- 
ther can we postulate an alteration of a single element in the climatic envi- 
ronment of a region without altering the relations of all the remaining ele- 
ments. Hence the interpretation of geological records in terms of climate 
become more and more difficult. 

Our conclusions, therefore, in reference to the climate of the Quater- 
nary are at the best somewhat arbitrary and are open to controversy. The 
weight of evidence and the impressions which one receives from the study 
the phenomena in question are such as to lead to at least a well-grounded 
opinion, even if some of the facts observed might be interpreted differently 
by different observers. 

The present arid climate of the Great Basin cannot be explained by 
saying that the temperature is high and consequently the water that is 
precipitated is rapidly evaporated. On the contrary, evaporation is rapid, 
probably for the reason that precipitation is moderate, or, perhaps more accu- 
rately, because the mean annual humidity of the atmosphere is low. In 
explanation of the present aridity some writers have attempted to show th«t 
as the prevailing winds blow from the Pacific, and consequently are obliged 
to cross the Sierra Nevada before reaching the Great Basin, the mountains 
condense their moisture, and hence they reach the region to the eastward 
as drying winds. In this explanation it is forgotten that the Sierra Nevada 
is scarcely, if at all, more humid than the Wasatch or some of the higher 
of the basin ranges, and that much of the Pacific slope is also an arid coun- 
try, although situated between the ocean and the mountains that are sup- 
posed to rob the winds of their moisture. Other explanations of the aridit}' 
of nmch of the region west of the Rocky Mountains have been advanced, 
but it remained for Captain Button to present the view that apparently has 
the strongest foundation.^ This writer explains the aridity by peculiarities 
of the currents of the Pacific. In brief, this theory assumes that the cur- 
rents from the north which follow the western border of the continent cool 
the air that is carried over them towards the land, this being the prevailing 
direction of the air currents of the region ; consequently, on reaching the 

wAmericaD Journal of Science, Vol. XXII, 1881, pp. 247-250. 



GLACIERS AND CLIMATIC OSCILLATIONS. 26d 

land, the air has its temperature increased, and thus becomes a dry wind. 
If this expUination of the present climatic condition of the Great Basin be 
accepted, it is evident that past fluctuations in the climate of the same 
region could be accounted for by assuming changes of direction in the cur- 
rents of the Pacific. 

Testinwmj of the Glaciers. — Thus far our discussion has been confined 
to the evidence afforded by the records of the ancient lakes. It is mani- 
fest that the glaciers which existed on the neighboring mountains during 
the time the lakes were flooded should furnish additional evidence bearing 
on the same question. 

The climatic conditions favoring the origin and growth of glaciers has 
recently been a subject of controversy. Some writers have claimed that 
the Glacial epoch was a warm period, in comparison with the present, and 
that the extension of the glaciers was due to an increase of precipitation 
caused by a greater evaporation over distant oceanic surfaces, the increased 
evaporation being caused by a general rise of the mean annual temperature. 
This hypothesis, we believe, was first suggested by Tyndall and Frank- 
land, and has been extended by Professor Whitney in his work on "Climatic 
Changes in Later Geological Times." A number of articles in various scien- 
tific journals have also been published in extension and support of the same 
assumption. 

It is beyond the scope of the present volume to enter into the theoret- 
ical discussion thus opened, nor is it necessary, as the arguments brought 
forward by the writers cited above have been controverted by Newberry, 
Dutton, Gilbert, and others, who adhere to what may be called the ortho- 
dox belief — having been held by the majority of writers on geological 
climate — that glaciers are an index of cold, and that their great increase 
during the Quaternary was due to a decrease in mean annual temperature. 
In other words, the winters during the Glacial epoch were longer or more 
severe than at present, and their snows not completely melted during the 
short summers. The conclusions reached by these writers is so entirely in 
accordance with all that has come under our own observation in reference 
to the existence of glaciers, that we do not hesitate in considering their de- 
terminations as final. The fact that the winter season in the Far West, for 
example, is the one that favors the accumulation of snow and the growth of 



266 GEOLOGICAL HISTOEY OP LAKE LAHONTAN. 

glaciers, while during the summer these conditions are reversed, seems 
enough in itself to show that an extension of the winter conditions, from 
whatever cause, for a greater portion of the year would favor the extension 
of the present glaciers and the formation of new ones, as well as the increase 
of the existing lakes and tlie flooding of valleys that are now arid through- 
out the year. Prolonging the winter conditions in temperate latitudes would 
therefore initiate a glacial epoch. This is the more evident as the climatic 
change necessary to cause an extension of the existing glaciers of the 
Sierra Nevada so as to approximate to their former magnitude, or the growth 
of the existing lakes of the Great Basin until they equaled the extent of the 
Quaternary water surface of the same region, need not be considered as a 
climatic change of great intensity. 

There are no records of the former existence of glaciers within the basin 
of Lake Lahontan, but the western border of its hydrographic basin was 
once buried beneath a vast accumulation of snow and ice that covered all 
the higher portions of the Sierra Nevada. TJie East Humboldt range, 
which forms a portion of the eastern border of the same drainage area, 
was also glacier-crowned. In the central portion of the basin, the Sho- 
shone, Star Peak, and Granite ranges rise to an elevation of about 10,000 
feet, and are reported by the geologists of the Fortieth Parallel Explora- 
tion to bear evidence of former glaciation about their summits. 

The former presence of extensive glaciers on the Sierra Nevada and 
Wasatch mountains, and of ice fields of less extent on some of the inter- 
mediate ranges, is sufficient to prove that during that time all the mountains 
of the region must have been snow-covered for at least a large portion of 
each year. This in itself — unless the temperature throughout the year was 
below freezing — would necessitate the formation of lakes in the inclosed 
basins between the ranges. In three instances in the Bonneville basin, and 
at four localities near Mono Lake, the glacial and lake records of Quaternary 
date overlap. The moraines at the western base of the Wasatch mount- 
ains which descend below the level of the Bonneville beach have been de- 
scribed by Mr. Gilbert;^* in this instance, however, the relative age of the 
moraines and lake terrac^es is indefinite. In the Mono basin a number of 



**Secourl Ann. Kep. U. 8. Gfol. Survey, p. 189. 



FLUCTUATION OF GLA0IEE8. 267 

glaciers of large size formerly flowed down from the High Sierra, which 
forms its western border, and deposited moraines of great magnitude, on 
which the terraces of the Quaternary lake, that formerly filled the basin to 
the depth of nearly 900 feet, are distinctly traced. The moraines at Mono 
Lake were carried out into the valley as parallel ridges, or morainal embank- 
ments as we have found it convenient to call them, which in several instances 
are prolonged for a considerable distance below the highest of the ancient 
beaches, and have terraces traced not only on their outer slopes but on the 
inner sides of the couches formerly occupied by glacial ice. In some in- 
stances deltas have been formed between the extremities of the morainal 
embankments. The proof is therefore conclusive that the greatest exten- 
sion of the glaciers preceded the maximum rise of the lake. How far the 
glaciers had retreated up the cafions before the lake occupied their former 
beds it is impossible to determine. It has also been found that the glaciers 
of the Mono basin had two or more periods of maximum extension, sepa- 
rated by times when the ice withdrew far up the canons through which it 
flowed. There were at least two well-marked glacial epochs in the Sierra 
Nevada. The lacustral records of the Mono basin indicate two periods of 
high water, corresponding, it is presumed, to the two main periods of glacial 
extension. All the facts known to us are in harmony witli the conclusion 
that the two humid periods recorded in the Bonneville and Lahontan basins 
were practically synchronous with the two periods of maximum extension 
of the Sierra Nevada glaciers. The fact that the greatest rise of the Qua- 
ternary lake occup}'ing Mono Valley occurred after the greatest expansion 
of the glaciers does not militate against this determination, but indicates 
that the melting of the snow and ice on the mountains contributed an un- 
usual supply of water to the lake, which then received its greatest flood. 
When mountains bordering an inclosed basin are loaded with snow and ice, 
it is evident that a rise of temperature will cause a flooding of the valleys. 
The analogy between the glacial climate of the Great Basin and the winter 
climate of the same region at the present time, thus finds another parallel. 
The evidence leading to the correlation of the two high-water stages 
of Lake Lahontan with the two Glacial epochs of the northern hemis- 
phere has already been indicated. Should this conclusion be sustained, 



268 GEOLOGICAL HISTORY OF LAKE LAHONTAK 

it follows that both series of phenomena resulted from a common climatic 
change. In the case of Lake Lahontan we have attempted to demonstrate 
that the change which caused the expansion of the lake was a lowering in 
the mean annual temperature, and that the periods of desiccation indicate 
a relative rise of temperature. This interpretation is in harmony with the 
verdict of the o*reat majority of writers in reference to the prevailing ele- 
ments in the climate of the Glacial epoch. In former times, as at present, 
the climate of various regions in the same latitude diflfered widely in refer- 
ence to humidity. The more humid regions were the areas of greatest 
glaciation. 

The discussion of the ultimate cause of the cold of the Glacial epoch is 
beyond the scope of the present report 

A summary of the writer's conclusions in reference to the climatic oscil- 
lations indicated by the fluctuations of Lake Lahontan is embodied in the 
following schedule : 

rProbableclimaticcoiiditions .. J-^ *»"« ^^ aridity; precipitaUon small; evaporation 
{ t rapid ; temperature high. 

1. Pre-Lahontan arid period < 

I e Lakes small, at times desiccated ; moantains tree fh>m 

i^^^^^ { glaciers.' 

rProbable climatic condiUons... 5 ^*^*P*^*'*»° moderate; evaporation decreased ; tern- 
I c peratnre low. 

2. First rise of Lake Lahontan . . < 

j r Large lakes in the valleys and glaciers in the monnt- 

l««»"»^ i ains. 

I Probable climatic conditions. . . 5 ^^^^^"^ precipitation ; evaporation rapid; tempera- 
i tare high. 
.Lakes smaUer tiian at present, and at times possibly 
^^qJI^ J desiccated; glaciers contracted and possibly com- 

t pletely melted. 

{Precipitation moderate, bat probably more copious than 
daring the first rise ; evaporation decreased ; tempei^ 
,. ..,.„^-.^ « . atnre low. 

{ Results Broad lakes and large glaciers. 

(Probable climatic conditions... J -^ ^™« **' «^* aridity; precipitation small; mean 
5. Post^Lahontan arid period .... J * temperature higher than at present 






Results Lakes desiccated and glaciers melted. 



6. Presenttime 



r Climatic conditions 5 P«c*Pitation smsll ; evaporation rapid ; mean temper- 

( atnre about SOP Fahr. 



r Country arid ; rivers small and fiuctuating ; lakes and 
^^""^^ \ glaciers small. 



CHAPTER IX. 
GEOLOGICAL AGE OF LAKE LAHONTAN. 

A review of the facts bearing on the age of Lake Lahontan necessi- 
tates some repetition, but seems desirable in order to present the evidence 
in a connected form. 

The reader is aheady aware that Bonneville and Lahontan were the 
largest of an extensive series of lakes which formerly occupied the valleys 
of the Great Basin. That the lakes here indicated — represented for conve- 
nience of reference on Plate I — were contemporaneous seems too positive 
to be questioned. The records in the various basins are identical, consist- 
ing of terraces, gravel embankments, sedimentary deposits, fossils, etc., in 
which no difference of age can be detected. Moreover, the existence of 
lakes in inclosed basins is dependent on climatic changes too broad in their 
effect to have been felt in a single valley without producing similar results 
in others near at hand That the lakes now under discussion, not only 
existed at the same time, but were also of a very recent date, is considered 
as abundantly proven by the fact that they left the very latest of all the 
completed geological records to be observed in the Great Basin. 

The fossil shells obtained from the sediments and tufas of Bonneville 
and Lahontan, and a few of the smaller sister lakes, all belong to living 
species. The mammalian remains discovered in the sediments of Lake La- 
hontan are the same as occur elsewhere in Tertiary and Quaternary strata. 
The spear head of chipped obsidian obtained in the upper Lahontan sedi- 
ments is considered good evidence — although as yet unsustained by other 
finds of a similar character — that man inhabited this continent during the 
last great rise of the former lake. 

260 



270 



OEOLOQIOAL HISTORY OF LAKE LAHONTAN. 



The greatest expansion of the waters of the Mono basin, occurred aub- 
eequent to the last extension of tlie Sien-a Nevada glaciers. Although this 
is the only instance known where the relation of the former lakes and gla- 
ciers of the Great Basin is clearly determinable, yet it seems a necessary 
inference that the other hikes of the same region attained their maximum at 
the same time. As the formation of glaciers and the extension of lakes in 
inclosed basins necessarily result from similar climatic changes, we corre 
late the two flood periods of Lake Lahontan with the two periods of maxi- 
mum extension of the Sierra Nevada glaciere. Again, from similarity of 
phenomena, the two periods of glaciation on the mountains of the Far West, 
are correlated in time with the two glacial epochs of northeastern America, 
as recognized by certain geologists. If this detennination is correct, it fol- 
lows that the last great expansion ot the lakes of the Great Basin occurred 
during the close of the Glacial period, and may be considered as contem- 
poraneous with the Champlain epoch of the eastern States. 

That the valleys of the Great Basin held lakes, at least at intervals, 
tliroughout the Quaternary, is not only probable, a priori, but is indicated 
by the great thickness of marls, cla^s and gravels that All these depressions. 
In the Bonneville bitsin these deposits have been penetrated to a depth of 
over 1,500 feet without reaching the underlying rock. That the lower 
portion of the material filling these depressions may be of Tertiary age, is 
certainly possible, but the records of the passage of the Tertiary into the 
Quaternary are so obscur^ and so little known that it is at present impossi- 
ble, at least in the lake-beds of the Far West, to say where the former ends 
and the latter begins. When Lake Lahontan began its existence will prob- 
ably never be known, except in ii general way; but that it reached its 
greatest extension in late Quaternary times and was approximately synchro- 
nous in its fluctuations with the advance and retreat of the Sierra Nevada 
glaciers during the Glacial epoch is a fair deduction from the evidence re- 
corded in the present volume. 

In regard to the time, as measm-ed in years, that has elapsed since the 
events described in this report took place, we have but shadowy evidence to 
otfer. It has been estimated by James Croll,** from astronomical data, that 
"ClimateandTiine, New York, 1»75. Chap. XIX. 



DATE OF THE GLACIAL EPOCH. 271 

the last Glacial epoch terminated about 80,000 years ago. Other investigators 
have approached tlie problem in different ways and reached widely discor- 
dant results. At present even an approximate measurement in years of the 
time that has elapsed since the last great retreat of the glaciers of the north- 
ern hemisphere seems impossible. Considering that Lake Lahontan fluc- 
tuated synchronously with the advance and ri treat of the glaciers during 
the Glacial epoch, we must conclude that its last evaporation followed the 
last great retreat of the glaciers. Our studies in the Far West have shown 
that there is no reason for supposing that the retreat of the Sierra Nevada 
glaciers was a sudden event, partaking of the nature of a catastrophe, or 
that the evaporation of the lakes which were supplied by the melting ice, 
was a matter of a few years. On the contrary, the glaciers are believed to 
have retreated slowly; with numy pauses, and the evaporation of the lakes 
to have extended through centuries. Even if the Glacial epoch can be 
proven to have terminated 80,000 years ago, there is no reason for consid- 
ering that desiccation of the lakes followed that event within many thou- 
sand years. As stated at the beginning of this paragraph, we have no defi- 
nite evidence to show that the Quaternary lakes were flooded a certain 
number of years since; but one familiar with the shore phenomena displayed 
in the valleys of the Far West cannot fail to be impressed with the perfec- 
tion with which these structures have been preserved. In many instances 
the embankments of gravel are as perfect in contour and as regular in 
slope as if constructed but a few years ago. Subaerial erosion is reduced 
to a minimum in such instances, however, for the reason that the structures 
are porous and absorb nearly all the rain that falls upon them, allowing it 
to percolate quietly through their interstices. Changes of temperature have 
but little power to alter their forms, owing to the large size of the inter- 
spaces and the readiness with which moisture is removed. The only ele- 
ments of subaerial erosion to which gravel embankments seem open to 
attack are the wind and the beating of rain During the lapse of centuries 
even these slow processes must effect appreciable changes, but as yet this is 
scarcely apparent in the embankments built in Lake Lahontan. It is evi- 
dent that gravel embankments in arid regions, so situated that they are not 
within the reach of stream erosion, may be considered among the most per- 



272 GEOLOGICAL HISTOPY OF LAKE LAHONTAN. 

manent of topographic forms; more constant, in fact, than the rocky mount- 
ain tops. It is not surprising, therefore, that the gravel structures fail to 
give evidence as to their age. 

We might consult the canons carved through Lahontan sediments since 
the recession of the lake for a time measure ; but the amount of erosion here 
apparent could have been performed by the existing streams in a few years, 
owing to the unconsolidated character of the strata and the high gi-ade of 
the streams caused by the lowering of their base level upon the withdrawal 
of the lake waters. Moreover the streams have meandered but little within 
their canons, thus indicating that these trenches have not been long finished. 
On the whole the canons indicate that but a brief period has elapsed since 
their excavation began. 

The tufa deposits of the basin have been exposed to erosion since the 
withdrawal of the lake waters, and might be expected to present some indi- 
cation of the time they had been subjected to subaerial erosion. These 
deposits are porous and open in structure and favor the absorption and 
retention of moisture. They are thus especially liable to the desti'uctive 
effects incident to the freezing of water in the interspaces of rocks, espe- 
cially as the rains and frosts of the Great Basin occur together. We may, 
therefore, expect tliat the subaerial erosion of the tufa deposits would be 
rapid, and that if they had been exposed for a long period they would 
exhibit marked evidence of waste and decay. The fact is, on the contrary, 
tliat these deposits are remarkably well preserved. The greater amount of 
fracture and displacement that has been observed has evidently resulted 
from the weight of the deposits when left unsupported by the waters in 
which they were formed. The only conclusion to be drawn from the tufa 
deposits in reference to the date of the last desiccation of Lake Lahontan 
is that their time of exposure has been short. 

Again, in reference to the shells strewn over many portions of the 
deserts which, in many cases, must have been left by the evaporation of the 
former lake, we find that these fossils, or semi-fossils, as they have been 
termed, are bleached white and have lost their epidermis, but are otherwise 
frequently as perfect as when inhabited by the mollusk to which they 
belonged. That these fragile bodies have been drifting about at the caprice 



DATE OF THE QUATEKNARY LAKES. 273 

of the winds for thousands of years without being destroyed is improbable, 
to say the least. 

Other facts bearing on the determination of the length of time that has 
elapsed since the close of the Glacial epoch may be observed in the caiions 
of the High Sierra, and have been described in part in a previous essay.®* 
We need not consult the moraines left by the ancient glaciers, as these, like 
the gravel embankments mentioned above, are comparatively stable struct- 
ures; but in the glaciated caiions there are numerous bosses and domes of 
granite and quartzite that have been exposed to the sky since the glacial 
ice was melted from above them. The ice-polish on these ledges is still 
conspicuous, and causes them to glisten in the sunlight as brilliantly as do 
similar surfaces adjacent to the existing glaciers of the High Sierra and of 
Switzerland. These smooth surfaces are still scored with fine hair-like 
lines, and the eye fails to detect more than a trace of disintegration that 
has taken place since the surfaces received their polish and striations. Here 
again we meet with the difficulty of applying quantitative measurements; 
but as there is a limit to the time that rock surfaces may retain their polish 
it seems reasonable to conclude that in a severe climate like that of the 
High Sierra it could not remain unimpaired for more than a few centuries 
at most. 

The cumulative weight of these various lines of inquiry is such as to 
lead to the opinion that the last desiccation of the Quaternary lakes of the 
Great Basin certainly occurred centuries but probably not many thou- 
sands of years ago. On the other hand, it might be argued that the pres- 
ence of the bones of the mastodon, camel, and horse in the lacustral clays, 
deposited during the last great rise of the lake, is abundant evidence of the 
antiquity of that event. The date of the various fluctuations of Lake Lahon- 
tan, as measured by the standard used in human history, thus remains an 
open question. 

^ Existing Glacioru of the United States, Fifth Annual Report U. S. Geological Survey. 

MoN. XI 18 



CHAPTER X. 

POST-LAHONTAN OUOGKAPIIIO MOVEMENTS. 

In our sketch of the origin of the Lahontan basin (atife, page 24), a 
brief account of the pre-Quatoraai-y faults of the region was given. As 
there stated, the area we are studying has been broken by profound frac- 
tures, which resulted in the division of tlie rocks into a great number of 
orographic blocks. 'I'he unequal displacenient of these gave origin to the 
various valleys that were occupied by the Quaternary lake. In the present 
chapter we wish to direct attention to similar movements of the earth's crust 
which have taken place since the evaporation of Lake Lahontan. 

The traveler in the Great Basin frequently sees low escarpments in 
lacustral beds and alluvial slopes, which form irregular lines along the bases 
of the mountains, and at times cross the valleys. In profile, these scarps 
present various appearances, as illustrated by the following sections. Where 
they cross alluvial slopes tliey usually exhibit a profile similar to that shown 
at a. In the open valleys they form a small cliff or steep ascent, joining a 




Fia, 3«,-Idiial croBS-prgBles of fHultod beii. 



horizontal plain below with a similar plain above, as indicated in section 
at b. On a mountain side the scarp is usually partially in rock and partially 
in alluvium, as represented at c. The course of the scarps is always irreg- 
ular, and sometimes forms zigzag lines that may be followed for many milsB. 



U S GLOLOOI^AL SURVEV 




POST - QUATKRNAHY KAUI.T LINKS 



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RECENT FAULTS. 275 

The scarps differ from the steep slopes bounding water-built terraces and 
einbankments-^that neither their upper or lower limits are horizontal for 
any considerable distance ; they are characterized by irregularity, and do 
not define the boundaries between deposits of different character. They 

• • • 

occur both above and below the highest beaches of the Quaternary lakes 
of the region where they are found, and exist in valleys that have a free 
drainage as well as in those that are inclosed and once held lakes. It is, 
therefore, evident that their origin is totally independent of the action of 
waves and currents, and it is equally clear that they cannot be the result 
of erosion. 

Scarps of this nature were first observed in the Great Basin by Mr. 
Gilbert, while examining the western base of the Wasatch Mountains, and 
were recognized as the result of recent orographic movements.^ In other 
words, they are fault scarps of very late origin. Their recency is shown 
by the fact that they commonly occur in Quaternary lacustral sediments and 
recent alluvial slopes, and form steep slopes of earth and gravel that are but 
little modified by erosion, and in many instances are bare of vegetation. 

In many cases, it is evident that they could not have existed in their 
present condition for more than a few years. Sometimes they are more 
than a hundred miles in length, and vary from a few feet to more than a 
hundred feet in height. 

Recent faults of this nature have been observed along the western base 
of the Wasatch Mountains, at the eastern base of the Sierra Nevada, and 
on the foot-slopes of many of the intermediate Basin ranges. In the La- 
hontan area recent fault scarps are a common feature in the topography of 
the valleys, and furnish one of the many interesting problems in the physi- 
cal geology of the region. 

All of the lines of post-Lahontan displacement that are actually known 
to exist in the Lahontan basin are sketched on Plate XLIV, with as much 
accuracy as the topography of the map admits. It is evident that our 
knowledge of this phenomenon is incomplete, as only the more recent dis- 
placements are apt to attract attention, for the reason that when erosion has 
modified the scarps it is frequently impossible to determine whether post- 

«» Second Annual Report U. S. Geological Survey, p. 192. 



276 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

Quaternary movement has taken place or not. Could the full extent of the 
recent fault lines he indicated on the map, it is prohable that they would 
form a complicated series of intersecting lines that would embrace nearly 
the entire area. 

The first feature of general interest that presents itself upon commenc- 
ing the study of these recent faults, is that they frequently, if not always, 
follow the courses of ancient displacements that are usually of great magni- 
tude. They are recent movements of ancient faults. 

The intimate association of thermal springs with recent faults is to be 
noticed not only in the basin of Lake Lahontan, but throughout the entire 
area of interior drainage thus far explored. It is also to bo noticed that the 
hottest springs almost invariably occur on the lines of displacement that 
have suffered the most recent movement. So nearly constant is this corre- 
lation, that wherever thermal springs occur, other evidences of recent oro- 
graphic movement are almost always at hand. The su^estion has been 
advanced in this connection^ that the high temperature of the springs is 
due to the friction of the rocks along the sides of the fault plane. It is the 
conversion of motion into heat. As, however, the faults result from a pro- 
found fracturing of tho earth's crust, it is evident that any water which finds 
its way into a fault may descend to great depths and consequently reach 
regions of high temperature ; it is more than probable, therefore, that the 
springs derive at least a portion of their heat from the internal heat of the 
eartli. It is imjjossible at ])reseut to determine how much of the heat affect- 
ing springs is caused by friction and how much is due to the prevailing' 
high temperature of the earth at great depths. Probably both causes con- 
spire to produce the I'esulta observed. 

The intimate association of the thermal springs of the Lahontan basin 
with recent displacements may be illustrated by comparing Plates VIII and 
XLIV, which will show that but a very few thermal springs occur in this 
area that are not closely associated with recent faults. 

The various lines of recent displacement in the Lahontan basin have 
so many features in common that it is unnecessary to enter into a detailed 
description of each. All that are represented on Plate XLIV, within the 

"Third AduuuI Kuport U. S, Oculogical Survey, p. 232. 



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EECENT FAULTS. 277 

borders of the ancient lake, exhibit scarps in lacustral beds and gravel de- 
posits, and are therefore more recent than the last rise of the lake. 
^ The appearance of the fault at the western base of the West Humboldt 
range is shown on Plate XLV ; the point of view being near the southern 
end of Humboldt Lake. The precipitous mountain face shown in the pic- 
ture is in reality an ancient fault scarp of grand proportions, which was 
somewhat eroded before the existence of Lake Lahontan. During the time 
the lake occupied Humboldt Valley its waves carved a number of terraces 
along the base of the mountains, which are represented in the sketch, and 
are familiar to many who have traveled over the Central Pacific Railroad. 
Between the highest terrace and the shore of the present lake there is an 
irregular line of cliffs — in part obscured by talus slopes — which has been 
produced by recent orographic movement This fault scarp is composed 
principally of cemented gravels of Lahontan age, but in places the rock 
forming the mountains may be seen beneath the clastic beds. The charac- 
ter of the section exposed at many localities along this fault is represented in 
diagram c, Fig. 36. This fault scarp may be traced continuously from the 
Mopung Hills northward, along the bases of the West Humboldt and Star 
Peak ranges, to the neighborhood of Winnemucca, a distance of over a hun- 
dred miles ; its full extent, however, remains to be determined. Throughout 
the greater part of its course it crosses alluvial slopes, with a fresh scarp 
from ten to twenty feet, or more, in height, its greatest magnitude being 
near its southern end. Along the eastern shore of Humboldt Lake it forms 
a nearly vertical escarpment, fully fifty feet high. At the Mopung Hills it 
divides into several branches, which may be traced to the border of the 
Carson Desert, and then become obscured. 

In describing the shore phenomena on the Niter Buttes, a spur of the 
main range, at the southern end of Humboldt Lake (see ante, page 112), 
some account was given of sloping terraces, which indicate that orograpliic 
movement must have taken place during inter-Lahontan time. We have 
evidence, therefore, that the fault along the west base of the West Humboldt 
range attained a great magnitude previous to the existence of Lake Lahon- 
tan, that it underwent some disturbance during inter-Lahontan time, and 



If 



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1 



278 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 

has increased its displacement fully fifty feet since the evaporation of the 
Quaternary lake. 

The hot springs at Hot Springs Station, on the Central Pacific Rail- 
road, occur on a line of recent displacement, which may be followed for a 
few miles, both north and south, from the present site of the springs. De- 
posits of extinct springs may be seen for a mile or more north of the present 
point of outflow, indicating that former openings, through which the spring 
rose, have been filled by calcareous deposits, thus compelling the waters to 
find other points of egress along the line of fracture. 

The recent fault on the east side of the Carson Desert is marked by a 
low scarp in alluvium, and a change in the drainage where the displace- 
ment crosses Alkali Valley. East of Borax Springs, situated in Alkali 
Valley on the line of fracture, the slope of the desert surface is eastward, 
. and conducts the drainage to the end of the valley where a lake of brine is 
formed, which on evaporating leaves a deposit of salt of economic import- 
ance. Alkali Valley is bordered on all sides by precipitous mountains, 
excepting where it opens into the Carson Desert, and formed a deep bay 
during the existence of Lake Lahontan. In passing from the Carson Desert 
\ into Alkali Valley no change in the nearly level desert surface is noticeable 

until the line of faulting is reached; the plain tlien inclines gently eastward 
as we have described. It is evident that this inclination of the desert surface 
has taken place in post-Lahontau times, and is due to a slight tilting of the 
orographic block on which Alkali Valley is located. 

The course of the fault indicated on Plate XLIV, as crossing the north- 
ern border of Mason Valley, is rendered conspicuous in the topography of 
the valley bottom by a scarp from ten to twenty feet high in lacustral mai*ls 
and clays, and by numerous thermal springs. This is probably a continu- 
ation or a branch of a displacement in Walker River Valley which presents 
a section of Lahontan sediments fully 150 feet high. In common with the 
majority of the recent displacement of northern Nevada, both ends of this 
fault are obscure and indeterminable. 

What is probably a continuation of the series of disturbances observed 
in Mason Valley is indicated by a recent scarp along the east base of the 
Wassuck or Walker Lake range. The influence of tliis displacement on 



;! 
I 

ii 



/> 



EEOENT FAULTS. 279 

the contour of the lake bottom is indicated to some extent by the soundings 
given on the map forming Plate XV. The lake is deepest in the immediate 
vicinity of the fault line. 

It is probable that the direction taken by Walker River on leaving 
Mason Valley was determined by orographic movement, as it does not fol- 
low what appears to have been its natural course, but the character of this 
change is difficult to describe. The former outlet of Mason Valley was 
through a narrow gorge leading to the Carson River which it entered at a 
point opposite the site of Camp Churchill. This would probably have been 
the course taken by the stream when the waters of Lake Lahontan were 
withdrawn for the last time, had not orographic movement caused a slight 
change in the slope of the valley and thus deflected the river to the right. 
This phenomenon will be better understood on consulting the accompany 
ing pocket map, where the ancient channel leading from Mason Valley to 
the Carson River is indicated. 

That portion of the great Sierra Nevada fault which defines the western 
border of Carson and Eagle valleys has undergone a recent displacement 
of from ten to thirty feet, as is shown by fresh scarps in earth and gravel, 
and also by the outflow of heated waters at several localities. The recent 
scarp in this instance has been followed all the way from near Carson City 
to beyond Genoa; the full extent of the movement, however, far surpasses 
these limits. 

The basin of Lake Tahoe is an orographic valley of the Great Basin 

type, but is situated at a high altitude in the Sierra Nevada on the border 

of the interior drainage area. With the exception of the hot springs at the 

northern end of the lake, no evidence is known to the writer tending to 

show that ther^ has been recent orographic movement in its immediate 
vicinity. 

The faults along the eastern base of the Pine Forest Mountains ; on 
the western margin of the Black Rock range, from Black Rock point north- 
ward, and at the northern base of the Harlequin Hills are all marked in 
the topography of the country by recent scarps that seldom exceed twenty 
feet in height. At numerous points along these lines of displacement 
thermal springs come to the surface. 



280 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

The large group of hot springs near Ward's ranch, on the western 
border of the Black Rock Desert, and the group at the east end of Granite 
Mountain, are both on lines of recent displacement. 

The fault that crosses the western border of Smoke Creek Desert differs 
from most others in the Lahontan basin in the fact that it traverses the 
valley at a considerable distance from the mountains. Its course is marked 
by numerous thermal springs, and by a low scarp which at times becomes 
too indistinct to be easily traced. There is but little question that this line 
of displacement is a continuation of the fault to be seen at Granite Mountain, 
which apparently comes to view again along the borders of the Black Rock 
Desert farther northward. The connection between these various frag- 
mental fault lines has not been traced, and we have represented on Plate 
XLIV only such portions as have actually been observed. The course of 
this fault across the southern portion of Smoke Creek Desert- is indicated 
by a low and somewhat rounded scarp with a nearly east and west strike. 
The springs along the fracture irrigate the desert sufficiently to admit of 
the growth of grasses and desert shrubs which mark its course by a line of 
verdure through the absolute waste. Farther northward, in the neighbor- 
hood of Sheep Head Spring, the fault changes its course and becomes nearly 
north and south in its trend; farther northward, still, it bends more to the 
eastward, and, finally, near Round Hole Sprinji;' it has an approximately 
east and west strike. Its course is thus nearly crescent-shaped, but it has 
many more irregularities than we are able to represent on the accompan)''- 
ing map. On the line of this fault near Buffalo Springs there are a number 
of tufa piles rising abruptly from the desert to a height of thirty or forty 
feet, which exhibit the three varieties of tufa that are characteristic of the 
Lahontan calcareous precipitates. It is evident that the nuclei of these 
deposits were formed by subaqueous springs, as described in a previous 
chapter, thus showing that the fracture along which they are situated must 
have existed during tlie time the desert was occupied by the ancient lake. 
In a few instances the tufa piles situated immediately above the line of 
fracture have been split from base to summit by a recent orographic move- 
ment, and are now parted by vertical fissures two or three feet wide, into 



EEOENT FAULTS. 281 

which a person can descend a number of feet lower than the surface of the 
* desert. 

The fault described in the last paragraph is at such a distance from 
the highlands to the westward that no alluviation has taken place in its 
neighborhood. There has, therefore, been no transfer of load from one 
side of the displacement to the other. The tlirown side of the fault under- 
lies the broad desert and was lightened previous to the last fault-movement 
by the removal of 500 feet of water from its entire surface. It is quite 
evident, therefore, from the nature of the facts, that the unequal loading of 
contiguous orographic blocks, wliich has been assumed as an explanation 
of fault movements in certain instances, cannot be considered an element 
in the present example. 

A fault along the northern side of Honey I^ake Valley shows about as 
great an amount of post-Lahontan movement as any in the basin. In this 
instance the trend of the fault is irregular, but in general its course is north- 
west and southeast; its hade is nearly perpendicular, and the recent displace- 
ment at times exceeds a hundred feet. The thrown block underlies Honey 
Lake Valley. From the position of the present lake and the direction of 
drainage in the valley, it seems evident that the mountains between Smoke 
Creek Desert and Honey Lake Valley must have been upheaved to pro- 
duce tliis fault. A similar but more gentle movement of the same mount- 
ain mass would account for the recent scarp described above which crosses 
the Smoke Creek Desert. 

The faults represented on Plate XLIV, to the north of the Lahontan 
drainage area, are of the same character as those already described, and 
will require but a word of explanation at this time. 

The recent displacement on the west side of Surprise Valley, California, 
has a throw varying from 20 to 50 feet, and may be traced for nearly a 
hundred miles across alluvial slopes and gravel embankments of Quaternary 
age. As in numerous other instances, its course is marked by thermal 
springs, some of which are of high temperature and aflFord a large volume 
of water. The fault along the eastern base of the Stein Mountains, Oregon, 
falls in this same category, and together with other similar displacements 



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EECENT FAULTS. 277 

borders of the ancient lake, exhibit scarps in lacustral beds and gravel de- 
posits, and are therefore more recent than the last rise of the lake. 
^ The appearance of the fault at the western base of the West Humboldt 
range is shown on Plate XLV ; the point of view being near the southern 
end of Humboldt Lake. The precipitous mountain face shown in the pic- 
ture is in reality an ancient fault scarp of grand proportions, which was 
somewhat eroded before the existence of Lake Lahontan. During the time 
the lake occupied Humboldt Valley its waves carved a number of terraces 
along the base of the mountains, which are represented in the sketch, and 
are familiar to many who have traveled over the Central Pacific Railroad. 
Between the highest terrace and the shore of the present lake there is an 
irregular line of cliffs — in part obscured by talus slopes — which has been 
produced by recent orographic movement This fault scarp is composed 
principally of cemented gravels of Lahontan age, but in places the rock 
forming the mountains may be seen beneath the clastic beds. The charac- 
ter of the section exposed at many localities along this fault is represented in 
diagram c. Fig. 36. This fault scarp may be traced continuously from the 
Mopung Hills northward, along the bases of the West Humboldt and Star 
Peak ranges, to the neighborhood of Winnemucca, a distance of over a hun- 
dred miles ; its full extent, however, remains to be determined. Throughout 
the greater part of its course it crosses alluvial slopes, with a fresh scarp 
from ten to twenty feet, or more, in height, its greatest magnitude being 
near its southern end. Along the eastern shore of Humboldt Lake it forms 
a nearly vertical escarpment, fully fifty feet high. At the Mopung Hills it 
divides into several branches, which may be traced to the border of the 
Carson Desert, and then become obscured. 

In describing the shore phenomena on the Niter Buttes, a spur of the 
main range, at the southern end of Humboldt Lake (see ante, page 112), 
some account was given of sloping terraces, which indicate that orographic 
movement must have taken place during inter-Lahontan time. We have 
evidence, therefore, that the fault along the west base of the West Humboldt 
range attained a great magnitude previous to the existence of Lake Lahon- 
tan, that it underwent some disturbance during inter-Lahontan time, and 



278 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 

has increased its displacement fully fifty feet since the evaporation of the 
Quaternary lake. 

The hot springs at Hot Springs Station, on the Central Pacific Rail- 
road, occur on a line of recent displacement, which may be followed for a 
few miles, both north and south, from the present site of the springs. De- 
posits of extinct springs may be seen for a mile or more north of the present 
point of outflow, indicating that former openings, througli which the springs 
rose, have been filled by calcareous deposits, thus compelling the waters to 
find other points of egress along the line of fracture. 

The recent fault on the east side of the Carson Desert is marked by a 
low scarp in alluvium, and a change in the drainage where the displace- 
ment crosses Alkali Valley. East of Borax Springs, situated in Alkali 
Valley on the line of fracture, the slope of the desert surface is eastward, 
and conducts the drainage to the end of the valley where a lake of brine is 
formed, which on evaporating leaves a deposit of salt of economic import- 
ance. Alkali Valley is bordered on all sides by precipitous mountains, 
excepting where it opens into the Carson Desert, and formed a deep bay 
during the existence of Lake Lahontan. In passing from the Carson Desert 
into Alkali Valley no change in the nearly level desert surface is noticeable 
until the line of faulting is reached; the plain then inclines gently eastward 
as we have described. It is evident that this inclination of the desert surface 
has taken place in post-Lahontan times, and is due to a slight tilting of the 
orographic block on which Alkali Valley is located. 

The course of the fault indicated on Plate XLIV, as crossing the north- 
ern border of Mason Valley, is rendered conspicuous in the topography of 
the valley bottom by a scarp from ten to twenty feet high in lacustral marls 
and clays, and by numerous thermal springs. This is probably a continu- 
ation or a branch of a displacement in Walker River Valley which presents 
a section of Lahontan sediments fully 150 feet high. In common with the 
majority of the recent displacement of northern Nevada, both ends of this 
fault are obscure and indeterminable. 

What is probably a continuation of the series of disturbances observed 
in Mason Valley is indicated by a recent scarp along the east base of the 
Wassuck or Walker Lake range. The influence of this displacement on 



INDEX. 



287 



Page. 

Krakatoa, Dust ejected from 146 

Kriig von Kidda ; on cr>-8tallization 216 

Lacoatral B(>diiDeut«, Color of 160 

La Ilontan, Baron, Lake named in honor of 1 

Lake batiina, Claaaification of '23 

, Formation of 23 

BouncvUlo 28, 106, 224, 26(>, ti69, 270 

Eagle 72 

Erie, Areaof 260 

Honey 55 

Horse 72 

Humboldt 00 

Huron, Area of 260 

Michigan 248 

, Area of 260 

, Bars of 02 

North Carson 40, 68 

Ontario, Area of 2C0 

Pyramid 66-63 

Saint Clare, Area of 260 

South Carson G8 

Superior, Area of. 200 

Tahoe 71 

, Analysis of water of 42 

Walker eo 

, Amount of salts in 225-227 

Winnemuoca 63-66 

Lakes, Freshening of, by desiccation 11 , 224 

Laurontiau 260 

Koceut changes of 70 

oi the Great Basin 10, 269 

Lahontan basin 227-230 

Composition of 225 

Soda 7a-8o 

Lamination 158 

Laurentian lakes 260 

I^Conte, Prof.John; on Lake Tahoe 71 

Life history of Lake Lahontan 238-249 

Lithoid tufa loo 

Little Humboldt Valley, Sand stones near 154 

McGoo, W J vU, 20, 126, 134, 138, 142, 247 

Madeline Plains, Ancient lake of 72 

Mammalian fossils 238 

Man in the Quaternary 247, 260 

Marble Buttes, Tufa fh)m 105 

Margaritana margaritifera 140 

Marl, White 149 

Marsh. Prof. O. C. ; on fosnils 238 

Mary's river [Humboldt] 40 

Mason Valley i.'jg, 141 

Merel ; inethtHl of fractional crj'Htallizatlon 183 

Mill City, Nevada, St.ctions near 131 

Mississippi Kiver 175 

Mollusks of i*y ramid Lake 62 

Lahontan basin 240-246 

Walker Lake 69 

on Ihe shore of South Carson Lake 69 

Mono basin, Ancient glaciers of 266-267 

, Contorted strata in 160, 161 

, Exploration of 19 

craters 147-148 

Lake 219,222,270 

, Tufafh>m iu5 

Mono Vallej', On>graphio stmctnn^ of 25 

Mopnng Hills ii>9 



Pagew 

Mormons, Settlementof 16 

Mountains of Lahontan basin 88, 39 

Mullen's Gap, Small fault near 164 

, White marl deposits near 151 

Needles, The, Pyramid Lake 60,66 

, Tufa from the 195 

New berry. Prof. J. S.; on Quaternary climate 266 

NiUrbuttes 109 

Norway, Volcanic dust from 146 

Oe-<>.au waters, General chemistr y of 178-181 

Oi^den River [the llmnboldt] 40 

Oolitic Baud 168,186 

now form ing in Pyramid Lake 61 

Oreana, Nevada, Sections at 129-130 

Origiu of Lahontan basin 24-28 

Orographic movements 274-283 

Osobb VaUey, Saltlieldsof 223 

Outlet of Luke Lahontan, Question of 32-35 

Owen's Valli^y eartbquakn 282 

, Faults in 25 

Pahutc K^iiigv, Structure of 27 

Phosgonito 217 

Physical history of Lake Lahontan 87-171 

Physiography of the Lahontan basin ^ 86 

PLiya mud. Analysis of 83 

Playas, Fommtion of 9,10,81,82 

Post-Lahoutau orographic movements 274-283 

Powell, M«J. J. W 17 

Pseudoiuorphs 213-218 

Pumiceous dust 146 

Pyramid Island in Pyramid Lake, Nevada 60, 66 

Lake, Analysis of water of 57-68 

described 66-64 

, Elevationof 101 

, Tufa from 196 

, White marl deposits near 151 

Quaternary climate 254-268 

man 30,247 

of King, Upper and Lower 144-145 

toi>ography 30 

Question of outlet of Lake Lahontan 27-35 

Quiun River 41 

RagtowD, So<la Lakes near 73 

Ramnay, Prof. A. C; on color of laeustral sediments 109 

Ricksecker, Eugene, Aid of vii, 20 

Recent extinction of mammuls 230 

Reno, Nevada, Elevation of 101 

River, Carson 43 

, Humboldt , 40 

, Quinn 41 

, Truckee 42 

, Biiurcution of 68 

, Walker 45 

waters, General chemistry of 172-175 

Rivers of the Lahontan basin 9, 40 

, Composition of 225 

Rocksalt 85 

Rockbridge Al iim Spring. Analysis of 177 

Rye Patch, Nevada, Sections near 130 

Salt deposits 84 

works in Lalioutan basin 232-235 

Sand Spi iug Salt Works 2.'M 

Santa liosa Mountains, Structure of 26 

Sand Sprini: PiiSH, Sand dunes near ... 155 

Sand Spring. White marl deposits near 150 

SchalTer's Spring. Honey Lake Valley, Analysis of 51 



288 



INDEX, 



Seft-clifl&i, De«criptionof ..89,99 

Seaaouftin the Great Basin U 

Sea water, Salts deposited from 184 

Section showing character of Carson oafion 44 

of Lahontan sediments 129-133, 141, 143 

l^ravel between tufa deposits 204 

tii& tower 209 

white marl deposit 149 

through Black Kock Desert 27 

Pah ate Range 27 

Pyramid and Winnemncca Lakes 27 

Sediments of Lake Lahontan 124-145 

Selenito Mountains named 60 

Sevier Lake 223,230 

Shells of the Lahontan ba«in 240-246 

, Semi-fossil 272 

Shore phenomena 87-99 

Sierr.i Nevada 166 

, Orographic stmctureof 25 

Sim]>son, Capt. J. H., in the Lahontan basin, Expedition 

of 17,46 

Sinter deposited from snbaSrial springs 55 

Sleeping Bear Bluff, Michigan, Shore phenomena near.. 92 

Smoke Creek Desert, White marl doposito in 152 

Soda industry in Nevada 79 

Lakes near Kagtown, Nevada 73-80, 219 

, Analyses of the water of 77 

Spearhead from Lahontan sediments 247 

Spring waters, General chemistry of 175-178 

Springs, Classification of 47 

, High Kock, Honey Lake Valley 52 

near Granite Mountain, Nevada 52 

The Needles, Pyramid Lake 60 

of the Black Rook Desert 62,58 

Lahontan basm 47-54 

, Extinct 64 

on lines of recent faulting 58,279 

rising in saline lakes 220 

Star Peak, Nevada, Former glaciers of 266 

Stockton, Utah, Shore phenomena near 119 

Stratification and lamination 168 

Stream channels. Ancient 156 

Structure of terraces and embankments 166 

Succession of salts deposited on evaporation 182-187 

tufa deposits 204-207 

Sulphur in spring deposits 54 

Surface markings on lake beds 168 

SurpHse Valley, Salt fields in 223 

Taylor, Dr. F. W., Analyses by .. .78, 83, 233, 234 

TaiioeLake 71 

Temperature of the Lahontan period 262-268 

Terrat^es. 88-89,98-99 

and embankments, Structure of 166 

sea-cliffs of Lake Lahontan 100-105 

Terrjico Point, Pyramid Lake 104 

Thames, Water of the 174 



Thinolite, Crystallographio study of 194-200 

not a pseudomorph aftor gaylusalte 214 

terrace 157,193 

Thinolitic tufa 192-201 

Topography of lake shores 87-08 

Trona 77 

Tmckee River Cafion, Exposures of Quaternary sedi- 
ments in 181-187 

, White marl depoeits in 160 

Miocene 144 

Narrows 184 

River 42,63 

Tufa 180 

, Chemical analyses of 203 

, Conditions favoring the deposition of 210-222 

, Dendritic 201-208 

deposited about nuclei 210 

deposited ft'om sublaonstral springs 00 

deposits. Erosion of 272 

distinguished from tuff. 13 

.Lithoid 190,208 

now formiog in Pyramid Lake 206 

WalkerLake 70 

, Sucooesion of deposits of 204-207 

, Thinolitio 192,208 

towers. Structure of 209 

Tuff distinguished from tufk 13 

Tyndall, Prof. John; on glacial climate 265 

ITnalaaka, Volcanic dust of 147 

Valleys of the Lahontan basin 86 

VV>lcanic dust 146 

Wadsworth, Nevada, Sections near 132-183 

Walker, Joseph, Explorations of 15 

Lake 69,188 

, Amount of salts in 225-227 

, Analyses of water of 70 

VaUey, Structure of 27 

,Tu£ain 198 

River 45-47,70.226 

Cafion, Exposures of Quaternary strat* 

in 138-143 

, Solids carried in solution in 176 

Warren, Lieut G. K 16 

Wasatch Mountains, Ancient glaciers of 266 

, Fault in 276 

Waters of inland seas 181 

, Analyses of {tee Analyses). 

Webster, A. L.; aid of vii,20,35 

Wheeler, Capt. G. M., explorations of 17 

White terrace in Pyramid Lake Valley 151-153 

Whitney, Prof. J. D. ; on geology of California 16 

; on glacial climate 265 

W innemucca Lake 66, 63-66 

, Sand dunes near 154 

Woodward, R. W., Analysis by 68 

Wright, George M., Aid of vii,20