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Full text of "Geology of the San Diego metropolitan area, California"

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California. Division of Mines 
and Geology, Bulletin. 




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Physical 
ScLLib. 



TIM 
24 
OB 
A3 
no. 200 






OLOGY OF THE $, 
.METROPOLITAN AREA 
CALIFORNIA 



Del Mar, La JoUa, Point Loma, 

La Mesa, Poway, and SWV4 Escondido 

7V2 minute quadrangles 







THE LIBRARY 

OF 

THE UNIVERSITY 

OF CALIFORNIA 

DAVIS 



o GEOLOGY OF THE 

SAN DIEGO METROPOLITAN AREA, CALIFORNIA 

Prepared in cooperation witli the City of San Diego 



SECTION A 



WESTERN SAN DIEGO METROPOLITAN AREA 
Del Mar, La Jolla, and Point Loma 7V2 minute quadrangles 
by Michael P. Kennedy 



SECTION B 

EASTERN SAN DIEGO METROPOLITAN AREA 

La Mesa, Poway, and SWV4 Escondido 7V2 minute quadrangles 
by Michael P. Kennedy and Gary L. Peterson 




BULLETIN 200 
1975 



P 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 
1416 9TH STREET, ROOM 1341 
SACRAMENTO, CA 95814 



UCD LIBRARY 



(1) 




STATE OF CALIFORNIA 

EDMUND G. BROWN JR., GOVERNOR 



THE RESOURCES AGENCY 

CLAIRE T. DEDRICK, SECRETARY FOR RESOURCES 



DEPARTMENT OF CONSERVATION 

LEWIS A. MORAN, DIRECTOR 



DIVISION OF MINES AND GEOLOGY 
THOMAS E. GAY JR., ACTING STATE GEOLOGIST 



\f n f 



III « 




(^ » 




CONTENTS 



SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA 

ABSTRACT 9 

INTRODUCTION 11 

GEOLOGIC SETTING 13 

PRE-EOCENE DEPOSITS 14 

Santiago Peak Volcanlcs 14 

Gabbro of the Southern California Bathollth 14 

Rosario Group 15 

Lusardi Formation 15 

Point Loma Formation 15 

Cabrillo Formation 15 

EOCENE DEPOSITS 15 

La Jolla Group 15 

Mount Soledad Formation 16 

Delmar Formation 16 

Torrey Sandstone 16 

Ardath Shale 18 

Scripps Formation 18 

Friars Formation 18 

Poway Group 19 

Stadium Conglomerate 19 

Mission Valley Formation 19 

Pomerado Conglomerate 19 

FACIES RELATIONSHIPS OF THE EOCENE ROCKS 20 

EOCENE BIOSTRATIGRAPHY 20 

POST-EOCENE DEPOSITS 29 

IVIiocene 29 

Andesite Dike 29 

Pliocene and Pleistocene 29 

San Diego Formation 29 

Lindavista Formation 29 

Bay Point Formation 29 

Pleistocene and Holocene Surficial Deposits 30 

Stream-Terrace Deposits 30 

Landslide Deposits 30 

Alluvium and Slope Wash 35 

Beach Deposits 35 

Artificially Compacted Fill 35 

STRUCTURE AND SEISMIC HISTORY 35 

REFERENCES CITED 38 



SECTION B - EASTERN SAN DIEGO METROPOUTAN AREA 

ABSTRACT 43 

INTRODUCTION 45 

PRE-EOCENE DEPOSITS 45 

Basement Complex 45 

Santiago Peak Volcanics 45 

Plutonic Rocks of the Southern California Bathoiith 47 

Rosario Group 47 

Lusardi Formation 47 

EOCENE DEPOSITS 47 

La Jolla Group 47 

Friars Formation 48 

Poway Group 48 

Stadium Conglomerate 48 

Mission Valley Formation 49 

Pomerado Conglomerate 49 



(3) 



POST-EOCENE DEPOSITS 49 

Pliocene and Pleistocene Rocks 49 

San Diego Formation 49 

Llndavista Formation 50 

Pleistocene and Holocene Surflclal Deposits 50 

Stream- Terrace Deposits 50 

Landslide Deposits 50 

Alluvium and Slope Wash 51 

STRUCTURE AND SEISMIC HISTORY 51 

MINERAL RESOURCES 53 

REFERENCES CITED 56 



(4) 



ILLUSTRATIONS 



SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA 

Plate 1A. Geology of the Del Mar quadrangle In pocket 

Plate 2A. Geology of the La Jolla quadrangle In pocket 

Plate 3A. Geology of the Point Loma quadrangle In pocket 

Photo 1. The San Diego coastal area and adjacent Peninsular Ranges province 
showing boundaries of the Del Mar, La Jolla, and Point Loma quad- 
rangles 11 

Photo 2. Unconformity between the Eocene and Upper Cretaceous rocks located 

300 meters north of Tourmaline Street in Pacific Beach, looking northeast 16 

Photo 3. Small slump that has occurred within the Ardath Shale as a result of slope 

undercutting and incompetent rock, looking southeast 30 

Photo 4, Torrey Pines State Park landslide, looking east 30 

Photo 5. Landslides that have occurred as a result of oversteepened slopes associ- 
ated with an erosional scarp, looking southeast along the Mount Soledad 
fault 31 

Photo 6. Ancient landslide deposits underlain by rocks of the Upper Cretaceous 

Rosario Group on Point Peninsula, looking west 31 

Photo 7. Fort Rosecrans landslide on Point Loma Peninsula, looking west 31 

Photo 8. Sunset Cliffs located on the northern part of the Point Loma Peninsula, 

looking east 35 

Figure 1, Index map 12 

Figure 2. Columnar section of the San Diego continental margin 13 

Figure 3, Diagrammatic sketch of the basement complex and superjacent strata. . 14 

Figure 4. Block diagrams of the interrelationship between Eocene fades in the San 

Diego coastal area 17 

Figure 5. Model of transgressive and regressive deposition 21 

Figure 6. Relationship of biostratigraphy to lithostratigraphy 23 

Figure 7. Index map of fossil mollusk localities 24 

Figure 8. Index map of fossil calcareous nannoplankton localities 25 

Figure 9. Index map of fossil mammal localities 26 

Table 1 . Clay mineral analyses 32 



SECTION B- EASTERN SAN DIEGO METROPOLITAN AREA 

Plate IB. Geology of the SW 1/4 Escondido quadrangle In pocket 

Plate 2B. Geology of the Poway quadrangle In pocket 

Plate 38. Geology of the La Mesa quadrangle In pocket 

Figure 1 , Location map 46 

Figure 2. Columnar section of the San Diego continental margin 47 

Figure 3. Schematic diagram of lithostratigraphic variations in the Poway Group 

and modern erosion surface 48 

Table 1 . Atterberg limits and particle size distribution 52 

Table 2. Mines, quarries, and pits in the La Mesa, Poway, and SW 1/4 Escondido 

quadrangles 54 



(5) 



<f 



SECTION A 

Del Mar, La Jolla, 

and Point Loma 

quadrangles 



(# 



ABSTRACT 



The Del Mar, La Jolla, and Point Loma quadrangles are underlain by sedimentary rocks of 
Late Cretaceous, Eocene, Pliocene, Pleistocene, and Holocene age that rest with angular un- 
conformity on a Mesozoic metamorphic and plutonic rock basement complex. The Tertiary and 
Quaternary sedimentary succession was deposited unconformably on the Upper Cretaceous strata 
In a northwest-trending basin herein referred to as the San Diego embayment. The most ahundant 
rocksj3i_tlie-San^Diego embayment a^re gently folded and faulted Eocene marine, lagoonal and non- 
marine rocks that form a northwest-trending, eastward-thinning section. These strata were laid 
down upon the older rocks during a period of regional tectonic downwarping. 

The jH:g-F"ne. ne rock s of the area from oldest to youngest belong to the Upper Jurassic San- 
tiago Peak Volcanics. mid-Cretaceous southern California batholiih. and the Upper Cretaceous 
Rosario Group. The Santiago Peak Volcanics are mildly metamorphosed and occur in the sub- 
surface throughout most of the southern California continental margin but are exposed in only a 

-few places within this area. The rocks consist of interlayered meta-andesite, meta-quartz latite, 
meta-shale, tuff, slate, and quartzite. A meager marine molluscan fauna from the meta-shale in- 
dicates a Late Jurassic (Portlandian) age. The Santiago Peak Volcanics are intruded by rocks of 
the southern California batholith. The batholithic rocks that crop out in the mapped area are mostly 
gabbros. These rocks are locally deeply weathered and difficult to distinguish from overlying non- 
marine Eocene strata that have been largely derived from detritus of plutonic origin. Deformation, 
uplift, and unroofing of the batholith occurred prior to the deposition of the Upper Cretaceous 
clastic marine and nonmarine strata of the Rosario Group. The basal formation of the Rosario 
Group is the Lusardi Formation, a nonmarine boulder fanglomerate that was deposited along the 
western margin of the tectonic highlands upon the weathered surface of the plutonic and metamor- 
phic rock. Clasts in the Lusardi Formation are composed of locally derived basement rocks. Good 
exposures of the Lusardi Formation occur approximately 16 kilometers (km) north of Del Mar and 6 
km east of Carlsbad where the conglomerate is overlain by the middle part of the Rosario Group, 
marine sandstone and siltstone of the Point Loma Formation. The Point Loma Formation is Cam- 
panian and Maestrichtian in age and underlies most of the Point Loma Peninsula and the hills 
southeast of La Jolla. It is conformably overlain by the uppermost part of the Rosario Group, marine 
sandstone and conglomerate of the Maestrichtian Cabrillo Formation. 

Nine partially intertonguing middle and upper Eocene formations composed of siltstone, sand- 
stoneT and conglomerate were deposited during two major transgressive-regressive cycles upon an 
_erosional surface of mild relief following uplift and erosion of the Upper Cretaceous strata. The suc- 
cession is in excess of 700 meters (m) thick and grades from nonmarine fan and dune deposits on 

~\Ue east through lagoonal and nearshore beach and beach-bar deposits to marine continental shelf 
deposits on the west near the present-day coastline. The age and environmental interpretation of 
the rocks is based on the mapped distribution of the lithofacies and by presence of fossil 
calcareous nannoplankton and foraminifers in the continental shelf succession, mollusks in the 
nearshore rocks, and vertebrate land animals in the nonmarine sequence. Flame structures and 
current ripple marks in the continental shelf deposits, cross bedding in the nearshore deposits, and 
cobble imbrications and paleo-stream gradients in the deltaic, lagoonal, and fluviatile deposits 
combined with their petrologic content indicate that the sediments were derived from local source 
areas to the east. 

The nonmarine facies of the Eocene formations are typically well indurated and cemented. The 
lagoonal facies are soft, friable, and poorly cemented. The nearshore facies are well indurated, well 
sorted, and locally concretionary. The marine deposits are typically fine grained, well indurated, and 
well cemented. 

Rocks of the Pliocene San Diego Formation, where preserved, rest unconformably upon the 
Eocene strata. The San Diego Formation Is in turn overlain by the Lindavista Formation, a com- 
bin^atTorPoT nearshore marine, beach, and nonmarine strata composed mostly of sandstone and 
cOrrglomerate. The Lindavista Formation was deposited on a broad wave cut terrace that extends 

~acr5ss the entire width of the area. The late Pleistocene Bay Point Formation and Holocene sur- 
ficial deposits complete the stratigraphic record. 



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Tectonic deformation within the area can be divided into two episodes: (1) pre- mid-Cretaceous, 
and (2) late Tertiary and Quaternary. The Santiago Peak Volcanics were chaotically deformed and 
partly overturned during the first episode. The less deformed rocks that have been faulted and gen- 
tly folded by the later episode include those of Upper Cretaceous and later age. Sediments ap- 
proximately 100,000 years in age have been vertically offset in excess of 20 m by youthful faults that 
transect the area. The most prominent of these include the Rose Canyon. Mount Soledad. Old 
Town, and Point Loma faults. Speculation has been made in recent literature that the Rose Canyon 
fault is related to the active Newport-lnglewood structural zone on the north and the San Miguel 
fault in northern Baja California on the south. Forty-four earthquakes of Richter magnitudes bet- 
ween 2.5 and 3.7 (M 2.5 and M 3.7) and having epicentral localities within the greater San Diego 
area have been recorded by the California Institute of Technology Seismological Laboratory since 
1950. It has been shown that the area has had a strain release of between 1 and 16 equivalent 
magnitude 3 earthquakes/400 km? for the 29-year period between 1934 and 1963. 

Seismically triggered landslides have occurred in the sea cliffs at Point Loma, La Jolla, and 
Torrey Pines. Most of the mapped landslides, however, are gravity slides attributable to soft in- 
competent material, ground water penetration, and oversteepened slopes. 

Sand and gravel deposits useable for concrete, bituminous, and ceramic aggregate underlie a 
large part of the area. Clay deposits useable for ceramics, fire clay, and expansible clay are also 
abundant but have not been exploited. The clay deposits are widespread and closely associated 
with expansive soils and surficial landsliding. 



(10) 




Photo 1. The San Diego coastal area and adjacent Peninsular Range Province showing boundaries of the Del Mar, La Jclla, and 
Point Loma quadrangles. 

GEOLOGY OF THE WESTERN SAN DIEGO METROPOLITAN 

AREA, CALIFORNIA 

Del Mar, La Jolla, and Point Loma quadrangles 

by Michael P. Kennedy"! 



INTRODUCTION 

In 1965 the California Division of Mines and 
Geology in cooperation with the City of San Diego 
began a comprehensive geologic investigation aimed 
at a better understanding of the geologic hazards 
that exist within the greater San Diego metropolitan 
area (Kennedy, 1967, 1969). This report is one 
product of that investigation and is complemented 
by a similar report on the La Mesa, Poway, and 
SWi/-* Escondido quadrangles (Kennedy and Peter- 
son, 1975). Together the Del Mar, La Jolla, and 
Point Loma quadrangles are approximately 350 
square kilometers (km^) in extent and constitute the 
western part of the greater San Diego metropolitan 
area (figure I and photo 1 ). 

The western San Diego metropolitan area is un- 
derlain by valuable sand, gravel, and clay resources 
deemed feasibly extractable in today's market for 



'Geologist, Californij 



1 of Mines and Geology 



use in the north county, Del Mar, La Jolla, Miramar, 
Lindavista and Point Loma areas. The are a is un- - 
derlain primarily by sedimentary rocITiTiowever, oc- 
casional outcrops of plutonic and metamorphic 
rocks do occur. Very small surficial landslides 
(mostly unmapped due to scale of map) associated 
with expansible clay deposits in the northern and 
eastern parts of the area are abundant. These land-_ 
slides are closely associated with the outcrops of 
Friars and Dclmar Formations. The rock units map- 
ped and discussed herein are shown in diagram- 
matic relationship in figure 2. 

Previous investigations that have been 
especially useful in this study include a ground 
water investigation by A.J. Ellis (1919), a 
stratigraphic and paleontologic thesis of the La Jolla 
quadrangle by M.A. Hanna (1926), studies of the 
Pliocene deposits of San Diego by L.G. Hertlein and 
U.S. Grant IV (I 939, 1944), a monograph on the 
mineral resources of San Diego County by F.H. 



(11) 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



^ y<> LAKE HODGES 

^/h ^■^AR'i !|3?T^^S.W. 1/4 ESCONDIDO QUADRANGLE 
...'Tr "\ LZk^ p.,„„,.„ (PiQtelB 




WOODSON MOUNTAIN 

POWAY 

QUADRANGLE 
-^ (Plate 2B) 

/ 

QUADRANGLE 
(Plate 3B) 



Figure 1. Index map stiowlng the location of the Del Mar, La Jolla. and Point Loma quadrangles. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



13 



C» 



COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN 




Qbp I '^''P- S°y Point Formation 

Qin ■•••• I Qln, Lindovisto Formation 

Tsd, Son Diego Formation 



Tp, Pomerodo Conglomerate 
Tmv, Mission Valley Formation 
Tst, Slodium Conglomerate 

Tf, Friars Formation 

Tsc, Scripps Formotion 
Ta, Ardoth Stiale 
Tt, Torrey Sandstone 
Td, Delmar Formation 
Tms, Mount Soledod 

Formation 
Kcss, Cabrillo Formation 

(sandstone part) 
Kccg, Cabrillo Formation 
(conglomerate part) 
Kp, Point Loma Formation 
Kl, Lusardi Formation 
Jsp, Santiago Peak Volcan 



Kg, Granitic rocks of the 
southern California 
bathollth 



Figure 2 Columnar section of the San Diego continental 
margin. 



Weber (1963), and the San Diego-El Centre 
geologic map sheet by R.G. Strand (1962). 

The author would like to extend special thanks 
to D.M. Morton and G.W. Moore of the United 
States Geological Survey for encouragement, help in 
the field, and many valuable discussions pertinent to 
this study. Acknowledgment is due also to M.O. 
Woodburne and M.A. Murphy of the University of 
California Riverside and Professor A.O. Woodford 
of Pomona College for long interest in this study 
and enthusiastic help in the field and laboratory; to 
D. Bukry, D.J. Golz, C.R. Givens, J. P. Kern, ED. 
Milow, W.J. Zinsmeister, and the late E.C. Allison 
for assistance in the paleontologic aspects; A.K. 
Baird for help in petrographic aspects; P.K. Morton, 
C.H. Gray, Jr., G.B. Cleveland, B.W. Troxel, F.H. 
Weber, Jr., Y.H. Smitter, R.G. Strand, G.L. Peter- 
son, and J.I. Ziony for many interesting discussions 
in the field and for reviewing the maps and 
manuscript. 



GEOLOGIC SETTING 

Pre-Eocene rocks in the southern Peninsular 
Ranges of California are subdivided into four major 
units. From oldest to youngest they include the Bed- 
ford Canyon Formation, Santiago Peak Volcanics, 
southern California batholith, and the Rosario 
Group. Together these units form the basement 



complex upon which the younger sedimentary suc- 
cession rests. See figure 2 and cross sections 
A-A' (plate lA), B-B', C-C (plate 2A), and D-D" 
(plate 3A). 

The Santiago Peak Volcanics (Black Mountain 
Volcanics of Hanna, 1926) rest with angular un- 
conformity on the Bedford Canyon Formation where 
the latter has been preserved. The Bedford Canyon 
Formation is not known to exist at the surface in 
this area. In the Santa Ana Mountains to the north, 
the Santiago Peak Volcanics have an exposed length 
of 1 30 km (Larsen, I 948), and to the south they ex- 
tend from the international boundary to near the 
center of Baja California (Allison, 1964). They oc- 
cur in the subsurface throughout most of the 
southern California continental margin (Hertlein 
and Grant, 1944; Gray et ai, 1971). 

The Santiago Peak Volcanics have undergone 
mild metamorphism and have been intruded by 
rocks of the southern California batholith. The 
plutonic rocks of the batholith that crop out in the 
mapped area are gabbros, which have a steeply in- 
clined contact with the older metamorphic rock. 

The southern California batholith forms the 
backbone of the Peninsular Ranges of southern 
California and Baja California and is nearly 1,500 
km in length extending from the Transverse Ranges 
on the north to the southern part of the Baja Califor- 
nia peninsula on the south. The batholithic rocks 
within the study area were named and described by 
Larsen (1948). 

Deposition of Upper Cretaceous clastic marine 
and nonmarine strata followed the emplacement, 
uplift, unroofing, and deformation of the southern 
California batholith (figure 3). The basal formation 
of the clastic succession is the Lusardi Formation, a 
nonmarine boulder fanglomerate that forms the base 
of the Rosario Group. The Lusardi Formation was 
laid down along the western margin of the tectonic 
highlands and upon a deeply weathered surface of 
the plutonic and metamorphic rock (Peterson and 
Nordstrom, 1970). The clasts of the Lusardi For- 
mation are composed essentially of these two rock 
types, suggesting a local source area (Nordstrom, 
1970). The Point Loma Formation is the in- 
termediate formation of the Rosario Group. It un- 
derlies most of the Point Loma Peninsula and the 
hills southeast of La Jolla and is conformably 
overlain by marine sandstone and conglomerate of 
the Cabrillo Formation. The Cabrillo Formation is 
the uppermost formation of the Rosario Group and 
is also exposed at Point Loma and La Jolla. 

The pre-Eocene basement terrain is locally 
decomposed to depths of 50 meters. In most areas 
where Eocene rock rests directly on the basement 
rock, the early Tertiary surface (sub-La Jolla un- 
conformity, figure 3) is marked by residual clay 
deposits of montmorillonite that grade downward to 
fresh basement rock and upward into the Eocene 
sedimentary rock. The decomposed granitic rock 
and clay were primary sources of sediment for the 
Eocene depositional basin and give rise to the 
granitic appearance of the arkosic sandstone of 
these sedimentary facies. 



14 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



l^^-^l Rocks of Eocene and later age 

L'^\y-\^ Rocks of the Rosario Group 

I^S^xl Rocks of the southern California batholith 

IW;V/| Rocks of the Santiago Peak Volcanics 



Sub-La Jolla 
Present day unconformity 
topography 



Sub-Rosario 
unconformity 



Intrusive contact between 
the Santiago Peak Volcanics 
and the southern California 
batholith 




Figure 3. Diagrammatic sketch 
of the basement complex and 
superjacent strata. 



PRE-EOCENE DEPOSITS 



Santiago Peak Volcanics 

The Santiago Peak Volcanics comprise an 
elongate belt of mildly metamorphosed volcanic, 
volcaniclaslic, and sedimentary rocks that crop out 
from the southern edge of the Los Angeles basin 
southward into Mexico. They were originally named 
"Black Mountain Volcanics" (Hanna, 1926, p. 199- 
204) for exposures in the northeast part of the area. 
Larsen (1948) substituted the name — Santiago Peak 
Volcanics — as the name "Black Mountain" was pre- 
empted. 

The volcanic rocks range in composition from 
basalt to rhyolite but are predominantly dacite and 
andesite. The succession is typified by a wide 
variety of breccia, agglomerate, volcanic 
conglomerate, and tine-grained tuff and tuff breccia. 
Highly silicified rock — probably tuff and a variety of 
dark, dense, tine-grained hornfels — occur locally. In 
the Del Mar quadrangle, fossil-bearing marine 
sedimentary rocks are interbedded with the volcanic 
and volcaniclastic rocks. Included with the Santiago 
Peak Volcanics are a number of small mildly 
metamorphosed gabbroic to granodioritic plutons 
which arc considered to have been feeders for the 
volcanics rather than parts of the southern Califor- 
nia batholith. 

The Santiago Peak Volcanics, which form 
elevated peaks immediately east of the area at Black 
Mountain, are hard and extremely resistant to 
weathering and erosion. Most of the volcanic rocks 
arc dark greenish gray where fresh and weather 
grayish red to dark reddish brown. The soil 
developed on the Santiago Peak Volcanics is the 
color of the weathered rock and s upports the growth 
of dense chaparral. 



Age estimates for the Santiago Peak Volcanics 
have ranged from Late Triassic (Hanna. 1926) to 
mid-Cretaceous (Milow and Ennis, 1961 ). Fife et al. 
(1967) reported latest Jurassic (Portlandian) fossils 
from a marine clastic part of the succession near 
Del Mar, and to date this constitutes the most 
reliable age for these rocks in the San Diego area. 



Gabbro of the 
Southern California Batholith 

Larsen (1948) named the batholithic rocks in 
the San Diego coastal area the Woodson Mountain 
Granodioriie, the Bonsall Tonalite, and the San 
Marcos Gabbro. Though most of the plutonic rocks 
in proximity to San Diego are quartz diorite and 
granodiorite, only gabbro crops out within this area. 
The gabbro varies considerably in texture and com- 
position but generally is coarse grained and dark 
gray. The chief mineral constituents are calcic feld- 
spar and pyroxene with minor amounts of quartz 
and biotite. 

Potassium-argon dates (Evernden and Kistler, 
1970) from a gabbro located 20 km northeast of Del 
Mar near San Marcos, and a quartz diorite located 
10 km southeast of Escondido are, respectively, 101 
and 105 million years. A lead-alpha date on zircon 
from quartz diorite in the Woodson Mountain area, 
20 km southeast of Escondido, is 105 ± 10 million 
years (Bushee ct al. 1963). 

Throughout most of its exposure, the gabbro is 
weathered and difficult to distinguish from overlying 
sedimentary formations, which are largely com- 
posed of weathered plutonic basement rock. Careful 
examination for relict features, such as small quartz 
veins, is necessary to distinguish the weathered rock 
from the overlying sedimentary strata. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



15 



Rosario Group 

The Upper Cretaceous Rosario Group is com- 
posed of clastic sedimentary rocks of marine and 
nonmarine origin assigned to the Lusardi, Point 
Loma, and Cabrilio Formations. 

Lusardi Formation 

The basal formation of the Rosario Group, the 
Lusardi Formation, was named by Nordstrom 
(1970) for exposures of boulder conglomerate near 
the confluence of Lusardi Creek and the San 
Dieguito River, 2 km north of the area in the Rancho 
Santa Fe quadrangle. 

These rocks consist of cobble and boulder 
conglomerate, with occasional thin lenses of 
medium-grained sandstone. Some of the clasts are 
10 m in diameter. The Lusardi Formation at the ex- 
posures within the northeast quarter of the Del Mar 
quadrarigle, and within theType'area to the north, 
has a maximum thickness of 125 meters. At the 
Holderness No. 1 well, 1 7 km southeast of the tip of 
the Point Loma Peninsula, rocks considered to 
belong to the Lusardi Formation are 82 m thick, 
whereas at the Point Loma No. 1 well, 10 km north 
of Point Loma, these rocks are 295-376 m thick 
(Hertlein and Grant, 1944, p. 38). The Lusardi For- 
mation at its type area is unconformably overlain by 
Eocene rocks, but 16 km to the north near Carlsbad, 
it is overlain conformably by siltstone and sand- 
stone of the Point Loma Formation (Kennedy and 
Moore, 1971b). 

The Lusardi Formation is considered to b e Late 
Cretaceous in age because it contains quartz diorite 
bouIdeHlleroded from the mid-Cretaceous southern 
California, batholith, which has a minimum age of 
105± 10 million years (Bushee et al., 1963), and it 
is overlain by the Point Loma Formation which con- 
tains Upper Cretaceous (Campanian) Foraminifera 
(Sliter, 1968). 

The Lusardi Formation is lithologically 
equivalent to the Trabuco Formation of the Santa 
Ana Mountains on the north (Nordstrom, 1970), to 
an unnamed fanglomerate near the base of the 
Williams Formation, also in the Santa Ana Moun- 
tains (Morton, 1972, p. 39), and to the Redondo 
Formation of Flynn (I 970) in northern Baja Califor- 
nia. 



Point Loma Formation 

The Point Loma Formation, the intermediate 
part of the Rosario Group, crops out along the sea 
cliffs on the west side of the Point L.oma Pemns4ila, 
and in the La Jolla sea cliffs from Bird Rock to La 
JoUa Shores Beach (plates 2A, 3 A). At its type locality 
at the tip of Point Loma, it has an exposed thickness 
of 83 meters. The^■ocks there are interbedded fine- 
grained dusky-yellow sandstone and olive -gray clay 
shale that occur in graded beds about 30 cen- 
timeters (cm) thick. 

Scuba-diving observations- 1860 m offshore 
from the type locality show that ledgy pavement-like 
sandstone, similar to that in the lower half of the ex- 
posed section, continues to a depth of at least 37 m 



(Turner et al., 1 968, p. 8). With a shoreline dip of 6° 
E., it is postulated that 190 m of section may be ad- 
ded below low-tide level to the observed thickness 
of the formation. This submarine information, com- 
bined with interpolation from well logs, suggests 
that the total thickness of the Point Loma Formation 
at its type locality is about 300 m (section D-D'). 

Fossil Foraminifera and calcareous nan- 
noplankton indicate a Late Cretaceous age for the 
Point Loma Formation (filter, 1968; Bukry and 
Kennedy, 1969). Foraminifera from near the base of 
the formation at Carlsbad are middle to upper Cam- 
panian in age, whereas those from the uppermost 
beds are lower Maestrichtian in age (Sliter, 1968). 

The exposed part of the Point Loma Formation 
correlates with the Williams Formation and the up- 
per part of the Ladd Formation in the Santa Ana 
Mountains (Popenoe et at., 1960) and with the mid- 
dle part of Seal's (1924) Formacion Rosario in nor- 
thern Baja California. 

Cabrilio Formation 

The Cabrilio Formation, the uppermost unit of 
the Rosario Group, is exposed on the Point Loma 
Peninsula from the southern tip north to Sunset 
Cliffs. At Pacific Beach in the sea cliffs, it is ex- 
posed from 300 m south of False Point to Bird Rock 
on the north and at La Jolla in an S-shaped belt 
around the noses of the Pacific Beach syncline and 
Mount Soledad anticline. In the sea cliff at its type 
section 250 m east of the new Point Loma 
lighthouse, it consists of massive medium-grained 
sandstone and cross-bedded cobble conglomerate 
containing fresh plutonic and metavolcanic clasts 
but lacking red porphyritic rhyolite-tuff cobbles 
characteristic of nearby Eocene rocks. 

Throughout the mapped area, the Cabrilio For- 
mation conformably overlies the Point Loma For- 
mation. The formation is 8 1 m thick at its type 
locality, where it is uncontorrnaSTy overlain by 
Pleistocene deposits. Along the sea cliff at False 
Point, it has a thickness of 170 meters. 

A clam from the east flank of Mount Soledad 
within the lower 5 m of the Cabrilio Formation has 
been identified as "Pharella" alta (Gabb) and 
assigned to the Maestrichtian (L. Saul, written com- 
munication, 1969). The Cabrilio Formation 
correlates with the upper part of the Formacion 
Rosario of Beal (1924) in northern Baja California 
and possibly with the upper part of the Williams 
Formation in the Santa Ana Mountains. 



EOCENE DEPOSITS 
La Jolla Group 

The La Jolla Group (La Jolla Formation of 
Hanna, 1926) ranges from moderately deep-water, 
fine-grained siltstone, to sandy beach and lagoonal 
facies, and coarse-grained continental sandstone 
and conglomerate. Deep water fine-grained facies 
predominate to the southwest, whereas the lagoonal 



16 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



and continental facies are more abundant to the nor- 
theast. These units include six partly intertonguing 
and partially time equivalent formations, which from 
oldest to youngest, are the Mount Soledad For- 
mation. Delmar Formation, Torrey Sandstone, Ar- 
dath Shale. Scripps Formation, and Friars For- 
mation (figure 4). 

Mount Soledad Formation 

Southwest of the Rose Canyon fault, which in 
Rose Canyon displaces rocks on its southwest side 
(figure 4 ; plate 2A; section B-B' ). an Eocene marine 
cobhic conglomerate and sandstone unit, designated 
the Mount Soledad Conglomerate (part of the Rose 
Canyon Shale Member of Hanna, 1926), rests un- 
conformably on Upper Cretaceous rocks of the 
Cabrillo Formation. This formation crops out 
around the Mount Soledad anticline in La Jolla and 
northern Pacific Beach and south of Mission Bay on 
the southwest Hank of the Pacific Beach syncline 
(plates 2A, 3A). Block diagrams 3, 5, and 6 (figure4) 
show the stratigraphic relationship of the Mount 
Soledad Formation and the overlying and partly in- 
tertonguing Ardath Shale, Delmar Formation, and 
Torrey Sandstone. At its type locality on Mount 
Soledad, the formation is 69 m thick and consists of 
cobble conglomerate with minor beds of sandstone. 
The conglomerate content of the formation is 
variable to the southeast where it is locally com- 
posed entirely of medium-grained sandstone. The 
conglomerate commonly overlies similar Upper 
Cretaceous conglomerate of the Cabrillo Formation. 
The presence of distinctive red porphyritic, soda 
rhyolite-tuff clasts in the Mount Soledad Formation 
differentiates it from the Cabrillo Formation. This 
difference is easily seen at a sea-cliff exposure 300 
m northwest of the end of Tourmaline Street in 
Pacific Beach where the two conglomerates are in 
contact (photo 2). The sandstone is moderately well 
sorted, subangular to subrounded, poorly indurated, 
and well bedded. It consists of quartz (75-80 per- 
cent), potassium feldspar (20-25 percent). 




'■■.yiii^^-i^^-'i.-.^-i-^'^;. 



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Photo 2. Uncontormity between the Eocene and Upper 
Cretaceous rocks located 300 meters north of Tourmaline 
Street in Pacific Beach, looking northeast. The Eocene rocks 
contain soda rhyolite-tuff clasts not found in the Upper 
Cretaceous conglomerates 



plagioclasc (1-2 percent), biotite (1-2 percent), and 
a trace of epidote, pyroxene, and hematite. 

The Ardath Shale, conformably overlying the 
Mount Soledad Formation, contains fossils which 
are lower middle Eocene in age (Bukry and Ken- 
nedy, 1969). The Mount Soledad Formation 
correlates with the basal part of the Santiago For- 
mation in the Santa Ana Mountains (Kennedy and 
Moore, 1971a). 

Delmar Formation 

The Delmar Formation (Delmar Sand Member 
of Hanna, 1926) is exposed from the northern edge 
of the area mapped for 9 km south to Soledad Valley 
where it is overlain by younger rocks(plate 1 A).The 
stratigraphic relationship of the Delmar Formation 
with the Mount Soledad Formation, Torrey Sand- 
stone, and Ardath Shale is shown in figure 4. 

Most of the Delmar Formation is dusky 
yellowish-green sandy claystone interbedded with 
medium-gray coarse-grained sandstone. Several 
resistant beds composed of Ostrea idriaensis Gabb 
and other brackish-water mollusks indicate a 
lagoonal origin. The sandstone is typically com- 
posed of quartz (80-85 percent), potassium feldspar 
(10-15 percent), plagioclase (1-2 percent), biotite 
(2-3 percent), and a trace of hematite, topaz, 
glauconite, and pyroxene. The claystone is com- 
posed of montmorillonite and kaolinite. 

The base of the formation is not exposed but is 
presumed to rest unconformably on Upper 
Cretaceous or older rocks (section A-A' ) or con- 
formably on the Mount Soledad Formation as do 
correlative formations to the north and south (sec- 
tion B-B' ). In its type section near the town of Del 
Mar and throughout the area, it is overlain 
gradationally by the Torrey Sandstone, with which it 
is also partly equivalent (figure 4). In the subsurface 
15 km north near Carlsbad, the Delmar Formation 
grades into the Santiago Formation, and its boun- 
dary with the Santiago Formation occurs directly 
below the northernmost depositional limit of the 
overlying Torrey Sandstone (Kennedy and Moore, 
1971a). 

The Delmar Formation is considered to be mid- 
dle Eocene in age because it is correlative in part 
with the Mount Soledad Formation on the south, the 
Santiago Formation on the north, and contains a rich 
Domcngine molluscan assemblage. 

Torrey Sandstone 

The Torrey Sandstone (Torrey Sand Member of 
Hanna, 1926) crops out continuously from the nor- 
thern boundary of the area 12 km south to Torrey 
Pines Golf Course and inland about 10 km (plates 1 A, 
2A). It has a maximum thickness of 60m and is com- 
posed of arkosic sandstone which is white to light 
brown, medium to coarse grained, subangular, and 
moderately well indurated. It is massive and broadly 
cross-bedded. The sandstone consists of quartz (85- 
90 percent), orthoclase (5-10 percent), plagioclase 
(less than 1 percent), biotite (1-5 percent), and a 
trace of hematite, epidote, zircon, tourmaline, 
pyroxene, and amphibole. At the type section at 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



17 




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CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



Torrey Pines grade on Highway 101, the contact 
with the underlying Deimar Formation consists of 
an alternating gradation between white sandstone 
beds above the dusky yellow-green t'ossiliferous 
claystone beds below. Approximately 13 km to the 
north, the Torrey Sandstone grades into and is 
overlain by the Santiago Formation. In Soledad 
Valley the lower part grades into and is overlain by 
the Ardath Shale and the upper part by the Scripps 
Formation (Kennedy and Moore, 1971a). The 
distribution and stratigraphic relationship of the 
Torrey Sandstone with respect to its related facies is 
shown in figure 4. 

The Torrey Sandstone is believed to have been 
deposited along a submerging coast on an arcuate 
barrier beach that enclosed and then later tran- 
sgressed over Deimar lagoonal sediments. Its 
deposition was arrested when submergence slowed 
and the shoreline retreated. Although the Torrey 
Sandstone contains only a few poorly preserved 
fossils and fossil casts, its middle Eocene age is fir- 
mly established by its interfingering relationship 
with the well-dated Ardath Shale. 

Ardath Shale 

The Ardath Shale (part of the Rose Canyon 
Shale Member of Hanna, 1926) crops out along the 
sea cliffs from Bathtub Rock in Torrey Pines State 
Park, south to the pier at Scripps Institution of 
Oceanography, where it is overlain by Pleistocene 
deposits (plates 1 A, 2A). From Rose Canyon it can be 
traced south to the northeast corner of Mission Bay, 
where it is overlain by younger rocks. In the nor- 
thwest corner of the area, it thins below the Scripps 
Formation as it grades into the Torrey Sandstone 
below. The stratigraphic relationship between the 
Ardath Shale and formations with which it in- 
terfingers is illustrated in figure 4. The Ardath Shale 
is predominantly weakly fissile, olive-gray shale. 
Concretionary beds containing molluscan fossils are 
common. Expansible claystone locally comprises as 
much as 25 percent of the unit and landslides are 
commonly associated with those areas. Sieve 
analyses indicate that the particle size distribution 
is 81 percent silt, 16 percent clay, and 3 percent 
sand. The clay is mostly kaolinite but mont- 
morillonite is also present. The sand consists of 
quartz (70-75 percent), potassium feldspar (15-20 
percent), biotite (5-10 percent), plagioclase (less 
than I percent), and a trace of zircon, tourmaline, 
pyroxene, and amphibole. 

The base of the Ardath Shale is not exposed at 
its type section in Rose Canyon (Kennedy and 
Moore, 1971a), but underlying outcrops at the type 
locality of the Mount Soledad Formation, 1 km to 
the west, reveal the contact on the Mount Soledad 
Formation to be conformable. The Ardath Shale is 
estimated to be 70 m thick at its type locality. It 
grades alternatingly and conformably into the 
overlying Scripps Formation. 

Abundant fossils, including mollusks and 
calcareous nannoplankton, permit an assignment of 
the Ardath Shale to the lower middle Eocene (Bukry 
and Kennedy, 1969). The unit correlates with the 



basal part of the Torrey Sandstone and with the mid- 
dle part of the Santiago Formation. 

Scripps Formation 

The Scripps Formation (part of the Rose 
Canyon Shale Member of Hanna, 1926) underlies 
much of the area from east of Del Mar on the north 
to the mouth of Mission Valley on the south (plates 
I A-3A). Along the coast, it extends from the middle 
of Torrey Pines Park to Scripps Institution of 
Oceanography. The type section of the Scripps For- 
mation is 1 km north of Scripps Pier, on the north 
side of the mouth of Blacks Canyon (Kennedy and 
Moore, 1971a). Here it consists of 56 m of pale 
yellowish-brown, medium-grained sandstone and 
occasional cobble-conglomerate interbeds. The 
sandstone is composed of subangular grains of 
quartz (75-80 percent), potassium feldspar (15-20 
percent), biotite (2-5 percent), plagioclase (less than 
1 percent), and a trace of epidote, pyroxene, tour- 
maline, sphene, and apatite. Both the basal contact 
with the Ardath Shale and the upper contact w ith the 
Friars Formation are conformable. Figure 4 
illustrates the stratigraphic relationship between the 
Scripps Formation and related facies. Several 
tongues belonging to the Scripps Formation occur in 
the section. The largest of these is mapped in the 
vicinity of Sorrento Valley (plate lA). 

Fossils are present but are less common in the 
Scripps Formation than in the underlying Ardath 
Shale. Because of its close conformity and partial in- 
tcrgradation with the Ardath Shale, the Scripps For- 
mation is considered to be middle Eocene. To the 
north near Encinitas it correlates with the upper part 
of the Torrey Sandstone and, farther to the north in 
the Santa Ana Mountains, with the middle part of 
the Santiago Formation. 

Friars Formation 

The middle and late Eocene Friars Formation 
(part of the Rose Canyon Shale Member of Hanna. 
1926) is the uppermost unit of the La Jolla Group. 
The rocks are nonmarine and lagoonal sandstone 
and claystone named for exposures along the north 
side of Mission Valley near Friars Road in the La 
Jolla quadrangle (Kennedy and Moore. 1971a). The 
sandstone is composed of quartz (75-80 percent), 
potassium feldspar (10-15 percent), biotite (5-10 
percent), plagioclase (less than 1 percent), and a 
trace of amphibole. pyroxene, hematite, and tour- 
maline. The claystone is composed of mont- 
morillonite and kaolinite. Friars Formation is 
predominantly a nonmarine and nearshore marine 
facies which reaches a maximum thickness of 50 m 
between Mission Valley and Carmel Valley. The 
sandstone is typically massive, yellowish gray, 
medium grained, and poorly indurated with 
subangular to subrounded grains. Caliche-rich sand- 
stone beds are locally interlayered with dark 
greenish-gray sandy claystone. Cobble conglomerate 
lenses and tongues of Huviatile origin are charac- 
teristic of the easternmost exposures. The Friars 
Formation rests unconformably on rocks of the 
basement complex and conformably on the Scripps 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



19 



Formation. It is in turn overlain by other sedimen- 
tary deposits of Eocene, Pleistocene, and Holocene 
age. The Friars and Delmar Formations are 
lithologicaiiy identical in their central and nor- 
theastern exposures, and they have been un- 
differentiated in these areas on the geologic map. 
The stratigraphic relationship between the 
Friars Formation and related facies is diagram- 
matically illustrated in figure 4. 



Poway Group 

The Poway Group (Poway Conglomerate of 
Hanna, 1926) includes three partly intertonguing 
and partially time equivalent formations, the 
Stadium Conglomerate, the Mission Valley For- 
mation, and the Pomerado Conglomerate. These 
rocks are primarily nonmarine in their easternmost 
exposures and nearshore marine and lagoonal in 
their westernmost exposures. 

Stadium Conglomerate 

The type section of the Stadium Conglomerate 
lies near the boundary between the La Jolla and La 
Mesa quadrangles along the northern wall of 
Mission Valley near San Diego Stadium (Kennedy 
and Moore, 1971a). At the type section the for- 
mation consists of a massive cobble conglomerate 
with a dark yellowish-brown coarse-grained sand- 
stone matrix. The conglomerate contains dispersed 
lenses of fossiliferous crossbedded sandstone. The 
fossils include calcareous nannoplankton of late? 
Eocene age. 

The Stadium Conglomerate is moderately well 
sorted with an average clast size in the cobble range. 
Clasts having diameters as large as .05 m do occur 
but are rare. The sandstone matrix constitutes less 
than 20 percent of the unit, but in local stratigraphic 
sections individual sandstone beds and lenses con- 
stitute 50 percent of the unit. 

The highly distinctive "Poway" clasts that occur 
only within Cenozoic deposits of southern Califor- 
nia and that typify the Stadium Conglomerate con- 
sist predominantly (up to 85 percent) of slightly 
metamorphosed rhyolitic to dacitic volcanic and 
volcaniclastic rocks and up to 20 percent quartzite. 
The source area for these clasts is controversial, 
and potential sources from the Mojave Desert to 
Sonora, Mexico, have been proposed (DeLisle etal., 
1965; Merriam, 1968; Woodford et al.. 1968; 
Minch, 1972). Based on direction of pinching and 
cobble imbrication, the clasts within the Stadium 
Conglomerate were deposited within the San Diego 
embayment by a westward-flowing river system. 
Based on clast size the conglomerates were 
probably derived from a now eroded source within 
150 km of their present position (Kennedy, 1973a). 

The Stadium Conglomerate is conformably un- 
derlain by the Friars Formation and is conformably 
overlain by the Mission Valley Formation. The 
stratigraphic relationship between the Stadium 
Conglomerate and genetically related Eocene 
conglomerate to the east is shown in figure 4. 



Mission Valley Formation 

The Mission Valley Formation, a predominan- 
tly marine sandstone unit, lies conformably upon the 
Stadium Conglomerate and is in turn conformably 
overlain by the Pomerado Conglomerate. It has a 
maximum thickness of 60 m and was named for ex- 
posures along the south wall of Mission Valley on 
the west side of State Highway 163 (Kennedy and 
Moore, 1971a). The sandstone is characteristically 
soft and friable, light olive gray, fine to medium 
grained, and composed mostly of quartz and 
potassium feldspar. The grains are subangular to 
subrounded and locally range in size from coarse to 
very fine sand. Plagioclase and biotite are also 
present but generally constitute less than 2 percent 
each. Cobble conglomerate tongues within the 
Mission Valley Formation, similar to Stadium 
Conglomerate, comprise up to 30 percent of sec- 
tions measured in the easternmost exposures of the 
area but less than 1 percent of sections measured 
along the westernmost outcrops. 

Because of the friable nature of the Mission 
Valley Formation, it lacks the bold topographic ex- 
pression displayed by the Stadium Conglomerate. 
Interbeds and tongues of claystone of brackish 
water origin locally compose 20 percent of the sec- 
tion. The clay is primarily montmorillonile but 
kaolinite is also present. The Mission Valley For- 
mation thins from the west to the east (figure 4) and 
pinches out in the eastern part of the Poway and La 
Mesa quadrangles. The rocks are often fossiliferous 
and contain a molluscan fauna in the western and 
central exposures and a land-mammal fauna in the 
eastern exposures. One molluscan assemblage, 
collected from the uppermost beds of the formation 
in a road cut 200 m due east of the Miramar Reser- 
voir filtration plant (elevation 238 m) at Lat. 32° 
54.8' N.; Long. 117° 05.7" W., is reported by C.R. 
Givens (written communication, 1970) to be charac- 
teristic of the upper Eocene (Tejon Stage) and 
correlative with the upper Eocene of Europe. 

Pomerado Conglomerate 

The Pomerado Conglomerate, the uppermost 
ft)rmation of the Poway Group, has a maximum 
thickness of 55 meters. It was named for exposures 
located at the divide between Carroll Canyon and 
Poway Valley along Pomerado Road east of the area 
in the Poway quadrangle (Peterson and Kennedy, 
1974). The Pomerado Conglomerate is late Eocene 
in age and is a massive cobble conglomerate 
lithologicaiiy identical to the Stadium 
Conglomerate. The contact between the Mission 
Valley Formation and Pomerado Conglomerate is 
conformable and gradational. The Pomerado 
Conglomerate is characterized by occasional thin 
beds, lenses, and tongues of light-brown medium- 
grained sandstone. One of the largest of these, 
which crops out east of the area near Miramar 
Reservoir in the Poway quadrangle, is designated 
the Miramar Sandstone Member (Peterson and Ken- 
nedy, 1974). Lithologicaiiy the Miramar Sandstone 
Member is identical to the Mission Valley For- 
mation but is stratigraphically higher and wholly 



20 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



contained within the Pomerado Conglomerate. It has 
a maximum thickness of 10 m in its type area and is 
considered to be late Eocene in age based on its 
superpositional relationship with the Pomerado 
Conglomerate and Mission Valley Formations. 



FACIES RELATIONSHIPS OF 
THE EOCENE ROCKS 



The Eocene rocks of the San Diego embayment 
were laid down on a narrow continental shelf and 
adjacent margin that extended northwest and 
southeast for more than 50 kilometers. Subsidence 
of the basin and repeated change in sediment tlux 
resulted in alternating advances and retreats of the 
shoreline. The advances are recorded by the 
deposition of time-lransgressive rock units and the 
retreats by their time-regressive counterparts (Ken- 
nedy, 1971; 1973). 

Nonmarine lagoonal and nearshore marine 
facies were deposited on the east and marine con- 
tinental shelf facies on the west side of the San 
Diego embayment. There are two lithostratigraphic 
groups divided into nine intertonguing formations 
that together are approximately 700 m thick. The 
formational names are those of Kennedy and Moore 
(1971a) and Peterson and Kennedy (1974). 
y- The two groups are the La Jolla and Poway. The 
/^ La Jolla Group is slratigraphically lower and lies 
/ predominantly west of the Poway Group. Deltaic 
conglomerate and sandstone, lagoonal sandstone 
/ and claystone, beach sandstone, and marine shale 
/ constitute the La Jolla Group. Deltaic conglomerate 
\ and sandstone, lagoonal sandstone, and littoral 
sandstone and siltstone comprise the Poway Group. 
/ Figure 4 illustrates the interrelationships of the 
rocks and the contact between the groups. 

Deposition occurred continuously in the San 
' Diego embayment for a period of nearly 10 million 
years during which time the regional tectonic down- 
warping of the basin took place. The subsidence is 
marked in the stratigraphic record by two prominent 
marine transgressions and two intervening 
/ ^egressions. 

There are two somewhat conflicting hypotheses 
used to explain the development of cyclic sedimen- 
tation of this type (Sears et al.. 1941). The cyclic 
stratigraphic succession that forms by either of the 
two is an intertonguing sequence of strata having 
time regressive and transgressive parts (i.e., marine, 
littoral, beach, nonmarine) that grade laterally and 
vertically with respect to each other. 

One hypothesis or model, which has been rejec- 
ted for the development of the San Diego em- 
bayment, involves alternating upward and downward 
movement of the marine basin and adjacent con- 
tinental land mass to create the necessary change in 
sea level. The erosion of previously deposited 
materials by waves, during times when uplift oc- 
curred faster than sedimentation, would have 



removed parts of the cyclic facies. The cycles in the 
San Diego embayment are gradational, complete, 
and considered to have originated under different 
conditions. (^ 

Another model, and the one suggested for the 
development of the Eocene facies here, is based 
upon continuous subsidence of the sedimentary 
basin with changes occurring in both the rate of sub- 
sidence and rate of sedimentation. Regressive 
deposits are formed by the slowing of subsidence 
and/or an increase in sedimentation which creates 
the outward building of the shoreline and 
shallowing by infilling of the basin. During periods 
of more rapid subsidence and/or the slowing of 
sedimentation rate, the basin deepens and tran- 
sgressive deposits are laid down. 

Figure 5 is a diagrammatic illustration of the 
second model. Beginning at the top of figure 5 with 
diagram A, subsidence is occurring at a rapid rate 
with respect to sediment influx. This shows the 
initial development of the lagoon, beach, and near- 
shore deposits. Diagrams B and C illustrate later 
time but with continued conditions as represented 
by A. Note that these units are time-transgres'sive 
and that sea level has advanced over the old land 
surface. Beginning with diagram D either a slowing 
in the rate of subsidence has occurred or the 
sedimentation rate has increased or both. As a 
result of this change, the first regressive deposits 
are formed and the shoreline retreats. 

A period of rapid subsidence and high sediment- 
ation marks the beginning of the first transgression, 
recorded by the deposition of the Delmar For- 
mation, Torrey Sandstone, and Ardath Shale. These 
sediments transgressed eastwardly over and beyond 
the Mount Soledad Formation into pre-Eocene 
basement rock (section B-B'). The Ardath Shale 
rests conformably upon the Mount Soledad For- 
mation at the type section of the Mount Soledad 
Formation located 600 m east of Easter Cross in La 
Jolla. The Torrey Sandstone rests gradationally 
upon the Mount Soledad Formation at the base of 
Indian Trail in the sea cliffs 3300 m north of 
Scripps pier and at the intersection of Carmel Valley 
and Soledad Valley (plate lA). The conglomerate 
shown within the lower Delmar Formation is con- 
sidered to represent the transitional facies between 
the Delmar and Mount Soledad Formations. 

As shown in figure 4 and plates 1 A-3A ,the tran- 
sgressive nature of these stratigraphic units is in- 
dicated by their superpositional and lateral relation- 
ship. The lagoonal deposits are predominantly low 
in the section and lie to the east and northeast of the 
beach-bar and marine deposits. The beach and 
beach-bar deposits grade laterally eastward and 
downward into lagoonal deposits and westward and 
upward into marine deposits. Marine deposits are 
high in the section and lie to the west of the beach 
and lagoonal deposits. 

A slowing in subsidence and/or an increase in 
sedimentation to a degree that allowed infilling of 
the embayment at a greater rate than subsidence 
marks the beginning of a retreating shoreline and 
the development of regressive deposition. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



21 








1 


F 




Basement rock 


M 


E^^ 


^ 


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i:^^ 



4 KILOMETERS' 



Fluviotile- 
nonmarine deposits 



Lagoonal Beach and neorshore Deep marine 

deposits marme deposits deposits 



300-1 
200- 



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METERS' 



Figure 5. Model of transgressive and regressive deposition. (Modified from Sears et at.. 1941) 



22 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



As shallowing occurred the lagoonal. beach, 
and marine deposits migrated westward creating a 
reversal in their superpositional relationship (figure 
4), Again the lagoonal rocks lie predominantly on 
the cast and marine rocks predominantly on the 
west, but the regressive lagoonal rocks comprise the 
upper part of the stratigraphic sequence and the 
marine rocks the lower part. 

The regressive lagoonal equivalent of the tran- 
sgressive Delm.'r Formation is the Friars Formation 
and that of the beach-bar Torrey Sandstone is the 
Scripps Formation. The Ardath Shale also has a 
trangressive and regressive phase; however, these 
have not been separated, as they constitute a con- 
tinuous section that is lithologically homogeneous. 

Interbeds, tongues, and lenses of cobble 
conglomerate composed of exotic tuffaceous clasts, 
mostly of rhyolitic composition, and the primary 
sediment of a significant westwardly or nor- 
thwestwardly flowing river system are abundant in 
this part of the section. The direction of transport is 
indicated primarily by cobble imbrication and 
paleostream channel mapping (Minch. 1972). In the 
central and eastern part of the embayment, thick 
deposits of these clasts form the Stadium and 
Pomerado Conglomerates. 

Renewed subsidence and/or a slowing of 
deposition marked a second transgressive cycle and 
rocks of nearshore marine and nonmarine origin 
were laid down. The transgressive nature of the 
strata can be detected by the superpositional and 
gradational relationship between and within the 
Mission Valley Formation and the Stadium 
Conglomerate. The Mission Valley Formation is the 
continuum and regressive equivalent of the Scripps 
Formation (figure 4). 

A final regressive conglomerate unit, the 
Pomerado Conglomerate (figure 4), has been preser- 
ved high in the stratigraphic succession. One short 
period transgression marked by the Miramar tongue 
near the Miramar Reservoir in the Poway 
quadrangle is the uppermost marine sandstone of 
the column. 



of the Tertiary mammal chronology can be directly 
compared with invertebrate chronologies (figure 6). 
Four major fossil groups have been collected 
from the Eocene rocks of the San Diego embayment. 
These include I) mammals, 2) mollusks, 3) 
calcareous nannoplankton, and 4) Foraminifera 
(figures 7-9). 

1) Mammalian fossils were collected from the Ar- 
dath Shale, Friars Formation. Stadium 
Conglomerate, and Mission Valley Formation. The 
collection has been studied (Golz. 1971, 1973) and 
found to be correlative In its stratlgraphically up- 
permost part with the North American Uinta C 
Mammal Age and in Its lowest part with Bridgerian 
Mammal Age. 

2) Molluscan fossils were collected from Mount 
Soledad Formation. Delmar Formation, Torrey Sand- 
stone. Ardath Shale. Scripps Formation. Friars For- 
mation, and Mission Valley Formation, The fossils 
have been correlated, using West Coast (Califor- 
nia) Molluscan Stages, with the Tejon Stage in the 
stratlgraphically uppermost part of the section, the 
"Transition Stage" in the intermediate part, and the 
Domengine Stage in the lower part (Hanna. 1926; 
Moore, 1968; C. R. Givens, written communication. 
1973). 

3) Calcareous nannoplankton have been collected 
from the Ardath Shale. Scripps Formation, Stadium 
Conglomerate, and Mission Valley Formation. The 
flora in the stratlgraphically lowest part of the sec- 
tion IS indicative of the middle Eocene. Lutetian 
Stage of Europe (Bukry and Kennedy. 1969). The 
flora from the uppermost beds collected is sparse 
and is questionably correlative with the lower part 
of the upper Eocene (D. Bukry. written com- 
munication, 1971). 

4) Foraminifera have been collected from the Ar- 
dath Shale. Scripps Formation, Friars Formation, 
and Stadium Conglomerate. The fauna from the 
stratlgraphically uppermost part of the section has 
been reported by Mallory (1959) to be correlative 
with his Narizian Stage (late Eocene age) and that 
from the lower part of the section with his Ulatlsian 
Stage (middle Eocene age). Stelneck and Gibson 
(1971) have studied Foraminifera from both the Ar- 
dath Shale and Stadium Conglomerate and report a 
middle Eocene and late middle Eocene age respec- 
tively. 



EOCENE BIOSTRATIGRAPHY 

The Eocene lithostratigraphic succession 
discussed in the preceding pages contains fossil 
organisms representative of deep water marine, lit- 
toral marine, lagoonal, and nonmarine fluviatile en- 
vironments. These fossils together indicate that the 
boundary between the middle and late Eocene lies 
lies near the boundary between the La Jolla and 
Poway Groups in the central exposed part of the San 
Diego embayment and that the middle and late 
Eocene boundary falls within the Uintan Mammal 
Age (Golz and Kennedy, 1971). This is later, 
relative to the base of the Uintan, than originally 
proposed (Wood et al.. 1941). The Eocene suc- 
cession of the San Diego embayment is presently the 
only place known in North America where this part 



The discussion that follows establishes the 
fossil composition of each of the nine 
lithostratigraphic units within the Eocene San Diego 
embayment and relates the West Coast (California) 
molluscan stages to the North American Mammal 
Ages and these two chronologies to the Eocene of 
Europe by way of correlations based on planktonic 
calcareous nannoplankton zones. 

A relatively rich molluscan assemblage has 
been collected from the middle part of the Mount 
Soledad Formation at localities I and 2 (figure 7; 
(plates 2A, 3A). These localities combined are repre- 
sented by M I in figure 6. The assemblage from these 
localities includes TurriiclUi iivasana iippliniw Hanna, 
Ficopsis coopcriiina Stewart, and Tejonia lajollacnsis 
(Stewart), all of which are restricted to the middle 
Eocene Domengine Stage of California (Givens, 
1974). 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



23 



GEOLOGIC 
COLUMN 


STAGE OR AGE 


STRATIGRAPHIC SEQUENCE, FACIES RELATIONSHIP, 
AND COMPOSITE FOSSIL LOCALITIES 


ABSOLUTE AGE 

(RADIOMETRIC) 

IN MILLIONS 

OF YEARS 


I 
o 

Q- 
UJ 


z 
< en 

UJ UJ 
O- o 

o< 

IT t- 
3« 
Ul 


3 = 


<2< 

U. UJ 

tins 

UJ< cc 


NORTH 

AMERICAN 

MAMMAL 

AGES 


FORAMINIFERA LOCALITIES F 1-2 
MOLLUSK LOCALITIES ■ M 1-6 
NANNOPLANKTON LOCALITIES N 1-3 
VERTEBRATE LOCALITIES V 1-4 


42 — 

43 — 

44 — 

45 — 
45 — 

47 — 

48 — 

49 — 

50 — 


UJ 

z 

LJ 
<_> 

o 

LlI 


LlI 

< 
_l 


Z 
< 

Z 

o 

»- 
a: 

< 


z 
o 

UJ 

»- 


z 
< 

E 
< 

z 


o 
< 

Z 
3 


^""--^ CONGLOMERATE 
MISSION ^~""^\ 

VALLEY V4 ^^>- 

FORMATION Ni, MG,,,^-"-^^ 

^^.^^""""^ STADIUM CONGLOMERATE 


a. 
o 

>\ 

o 
a. 

a. 

! 


z 
o 
l- 
<n 
z 
< 

1- 


< 

Z 


^...^^ ^^^"^Ms^^^^^^-E^i!!!^ 

^^^■^^SCRIPPS^^^^ ~~~ ^ — -. 
^^^FORMA-^^^PRIARS 

^\„^^^T10N ^^^^ORMATION 

ARDATH SHALE ^----s^^M4 ^"^v,^^ 

FI.NI, M3,VI J^^ -^^v^, 

^-^^TORREY ^„.-<T^ DELMAR 
^^.^--^ANDSTONE^^,^-'-^ "^^ FORMATION 


UJ 

_J 

Q 
Q 

2 


z 
< 

1- 

LlI 

t- 


z 
< 

to 

(- 
< 

3 


UJ 

z 

o 

z 

UJ 

2 
o 

Q 


< 

< 

1- 

z 

3 


Z 
< 

a: 

UJ 

o 

cr 
m 


Ml ^_____..~---''^ 
MOUNT SOLEDAD FORMATION___^^ 

^^zo^^^^^^^ ' (Pre-Eocene rocks) 


a: 

< 

UJ 


z 

< 

UJ 
(T 

a. 

>- 


1 

< 
O 


z 
< 

H 

z 

UJ 
0. 


i 
o 



Figure 6. Relationship of biostratigraphy to llthostratigraphy. 

The upper contact between the Mount Soledad 
Formation in its type section near La Jolla with the 
overlying Ardath Shale is conformable. The age of 
calcareous nannoplankton in the Ardath Shale at 
localities 9 and 1 1, less than 25 m above this con- 
tact, are middle Eocene in age (Bukry and Kennedy, 
1969). The age assigned to the middle and upper 
parts of the Mount Soledad Formation is middle 
Eocene. 

The Mount Soledad Formation interfingers with 
the Delmar Formation to the north where a rich 
molluscan fauna has been collected from rocks at 
localities 3, 4, and 5 (figure 7; plate 1 A). These 
localities combined are represented by M2 in figure 
6. 

Horizons composed of nearly pure fossil shell 
material, mostly derived from brackish-water 
oysters, primarily Ostrea idriaensis Gabb, are abun- 
dant in the Delmar Formation. Tejonia lajollaensis 



(Stewart), restricted to the Domengine Stage of 
California (Givens, 1974), has been collected at 
localities 3 and 4. 

Because the Delmar Formation is also 
chronologically correlative with parts of the Ardath 
Shale (figure 4), the Delmar Formation is assigned a 
middle Eocene age. Based on a similar age, 
stratigraphic position, lithology, and environment of 
deposition — the Delmar is considered to correlate 
with the lower part of the Santiago Formation in the 
Santa Ana Mountains to the north. 

A sparse molluscan fauna was collected 
stratigraphicaily above the Delmar Formation from 
the Torrey Sandstone. The fauna consists of casts of 
Ostrea idriaensis Gabb and unidentifiable fragments 
of other pelecypods. A middle Eocene age is again 
assigned to the Torrey Sandstone on the basis of its 
interfingered relationship with the Delmar For- 
mation and Ardath Shale. 



24 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 




^ 



Figure 7. Index map of fossil mollusk localities. (See plates 1A-3A and plate 2B (Kennedy and Peterson. 1975) for detailed locations.] 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



25 




Figure 8. Index map of fossil calcareous nannoplankton localities. (See plates 1A, 2A and plate 2B, 3B (Kennedy and Peterson, 1975) 
for detailed locations.) 



26 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 




^LACM 65190 
UCMP V687I 

vUCMP V6893 



Figure 9. Index map of fossil mammal localities. (See plates 1A. 2A and plate 3B (Kennedy and Peterson, 1975) for detailed locations.) 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



27 



Fossil mollusks, calcareous nannoplankton, 
mammals, and Foraminifera have been collected 
from the Ardath Shale. The molluscan fauna was 
collected from localities 6 through 16 (figure 7; 
plates lA,2A).The localities combined are indicated 
by M3 in figure 6. The calcareous nannoplankton 
flora was collected from localities 1 through 1 1 
(figure 8 ; plates 1 A, 2A). These localities combined are 
indicated by Nl in figure 6. Fossil mammals have 
been collected from Los Angeles County Museum 
localities LACM 6673, LACM (CIT) 456, and 
LACM 1401 and from the University of California, 
Berkeley, locality UCMP V6884 (figure 9; plates 1 A, 
2A). These localities are combined in figure 6 as 
VI. Foraminifera have been collected from the 
Ardath Shale at a locality 1.5 km north of its type 
section in Rose Canyon (Steineck and Gibson, 1 971 ). 
This locality is indicated by Fl in figure 6. 

The molluscan assemblage collected includes 
Turritella uvasana applinae Hanna, f(copii.9 cooperiana 
Stewart, and Tejonia lajollaensis (Stewart), all of 
which are restricted to the Domengine Stage of 
California (Givens, 1974). Calcareous nan- 
noplankton from localities 6 through 9 occur at the 
same stratigraphic interval as mollusks from 
localities 10 and 11. Nannoplankton locality 9 
(figure 8;plate 2A), locality L 1 3 of Bukry and Ken- 
nedy (1969), yields fossils indicative of an early 
middle Eocene age (Discoaster sublodoensis zone). 
These include Coccolithus eopelagicus (Bram\ene and 
Riedel), Coccolithus pelagicus (Wallich), Helicopon- 
tospaera seminulum lophota (Bramlette and Sullivan), 
Discoaster distinctus Martini, and Discoaster bar- 
hadiensis Tan. Calcareous nannoplankton, also of 
early middle Eocene age {Discoaster sublodoensis 
zone), were collected from locality 1 1 (figure 8; 
plate 2A) in Rose Canyon from the type section of 
Hanna's (1926) Rose Canyon Shale Member. 
Steineck and Gibson (1971, p. 477) collected from 
this same locality and reported that the "occurrence 
of Subhotina patagonica Todd in both the Rose 
Canyon Shale and Cozy Dell Formation suggests 
time-equivalence of the two units (early middle 
Eocene in age)." 

The fossil mammals collected from the Ardath 
Shale have been reported by Golz (1973) to be of 
Uinta A or Bridgerian Age. However, since these 
land animals were transported to a marine 
depositionai environment, it is possible that they are 
older than the early middle Eocene rocks in which 
they lie. 

The Ardath Shale is conformably and 
gradationally overlain by richly fossiliferous rocks 
of the Scripps Formation. Fossil mollusks were 
collected within the stratigraphically lower and in- 
termediate part of the Scripps Formation from 
localities 17 through 23 (figure 7; plates 1 A, 2A) and 
are indicated together as M4 in figure 6. Mollusks 
were also collected from the upper part of the 
Scripps Formation near its contact with the Friars 
Formation at localities 24 and 25 (figure 7; plate 2A) 
and are indicated together as M5 in figure 6. 

A molluscan assemblage from a conglomerate 
at the base of the Scripps Formation 400 m north of 



its type section at locality I 7 (figure 7; plate 1 A) in- 
cludes Turritella andersoni lawsoni Dickerson, 
Turritella uvasana applinae Hanna, Tejonia lajollaensis 
(Stewart), and Ficopsis cooperiana Stewart. These 
fossils together indicate a Domengine Age (Givens, 
1974). An assemblage from locality 25 (figure 7; 
plate 2A) 20 m below the contact between the Scripps 
Formation and the overlying Friars Formation about 
400 m west of the type section of the Friars includes 
Nekewis io (Gabb) and Ectinochilus conalifer 
supraplicatus (Gabb). The upper part of the Scripps 
Formation based on the co-occurrence of these 
species is considered to belong to the "Transition 
Stage" and to be middle or late Eocene in age (C. R. 
Givens, written communication, 1973). 

The Scripps Formation is in part laterally 
equivalent to and in part conformably overlain by 
rocks of the Friars Formation. Mollusks were 
collected within the Friars Formation from near the 
gradational boundary with the underlying Scripps 
Formation at localities 26 and 27 (figure 7; plate 2A). 
These localities, combined because of their close 
stratigraphic proximity to locality 24 and 25, also 
are indicated by M5 in figure 6. The mammal fauna 
was collected from seven localities in the Mission 
Valley-Mission Gorge region. These include the 
University of California, Riverside, localities UCR 
RV 7046, RV 67112, RV 7047, RV 7049, RV 
7050, RV 68151, and RV 68152; University of 
California, Berkeley, localities UCMP V6872, V 
6873, and V6888; and Los Angeles County Museum 
localities LACM (CIT) 250 and 314 (figure 9; 
Kennedy and Peterson, 1975, plate 38 ). These 
localities together are indicated by V2 in figure 6. 

The molluscan fauna collected includes Nekewis 
io (Gabb) and Ectinochilus canalifer supraplicatus 
(Gabb). These species together suggest that the 
lower part of the Friars Formation belongs to the 
"Transition Stage" and is middle and late Eocene in 
age (Givens, 1 974). 

The mammalian fauna collected from the Friars 
Formation has been studied by Golz (1973). He 
reports that the stage of evolution of the artiodactyl 
fauna from the Friars Formation in the upper 
Tecolote Creek and Mission Valley-Mission Gorge 
area is indicative of Uinta B Age. 

Fossil calcareous nannoplankton, mammals, 
and planktonic Foraminifera have been collected 
from the Stadium Conglomerate. The nannoplankton 
were collected from a siltstone interbed at locality 
14 (figure 8;plate 3B, Kennedy and Peterson, 1 975) 
near the intersection of Murphy Canyon and 
Mission Valley. This locality is indicated as N2 in 
figure 6. The mammalian fauna was collected from 
Los Angeles County Museum locality LACM 1723 
and from University of California, Berkeley, locality 
UCMP V6840(figure9; plate3B, Kennedy and Peter- 
son, 1975). Together these localities are indicated 
as V3 in figure 6. The Foraminifera were collected 
from nannoplankton locality 14 by Steineck and 
Gibson (1971). This locality is indicated as F2 in 
figure 6. 

The nannofossils collected include 
Reticulofenestra umbilica (Levin) and Discoaster 



28 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



tlistinctus Martini. Because Reticulofenestra umbilica 
ranges trom the upper middle Eocene to lower 
Oligocene, the age of these samples based on nan- 
not'ossils is questionable. 

The mammalian fauna, which occurs 
siratigraphically higher and to the east of the marine 
fauna and flora,,has been correlated with the Uinta B 
or low Uinta C (Golz, 1973). 

Foraminifera from the Murphy Canyon locality 
include Cloborotaloides stiieri Bolli and Trun- 
coroialoides coUacteus Finlay (Steineck and Gibson, 
1971, p. 478). Though Steineck and Gibson state 
that this "co-occurrence suggests equivalence with 
upper middle Eocene strata", Jenkins (1965, figure 
2) considers that the occurrence of these two 
species indicates a restricted upper Eocene age. The 
foraminiferal assemblage collected from the Stadium 
Conglomerate lies near the boundary between the 
middle and upper Eocene based upon the coccolith 
assemblage with which it is interbedded. 

The Stadium Conglomerate is conformably 
overlain by richly fossiliferous strata of the Mission 
Valley Formation. The fossils include mollusks, 
calcareous nannoplankton, and mammals. The 
mollusks were collected from localities 28 through 
33 (figure 7;plate2A; and plate 2B , Kennedy and 
Peterson, 1975). These localities combined are in- 
dicated by M6 in figure 6. The fossil nannoplankton 
were collected from locality 15 (figure 8; plate 2B, 
Kennedy and Peterson, 1975). This locality is 
shown by N3 in figure 6. The fossil mammals have 
been collected from University of California, River- 
side, locality UCR RV 7048, University of Califor- 
nia, Berkeley, locality UCMP V6871 and Los 
Angeles County Museum locality LACM 65190 
(figure 9; plate 3B, Kennedy and Peterson, 1975). 
Together these localities are indicated as V4 in 
figure 6. 

The molluscan fauna collected from localities 
28 through 32 include Tellina tehachapii Anderson 
and Hanna, Matroccillisia undersoni Dickerson, and 
Crassdtellii uvusuna s. s. Gabb. These species when 
considered together are characteristic of the upper 
Eocene Tejon Stage of California (Givens, 1974). 
Mollusks collected from locality 33 which is ap- 
proximately 25 m stratigraphically higher in the sec- 
lion than locality 28 include Tiirritella uvasana 
siiri^eanti (Anderson and Hanna) which Givens 
(1973) considers restricted to the upper part of the 
Tejon Stage. 

The calcareous nannoplankton flora collected 
from locality 15 is sparse but includes several 
distinctive species including Reticulofenesiru iim- 
hilica (Levin) and Discoaswr distinctus Martini, which 
together suggest either a late middle Eocene or early 
Eocene age. 

The artiodactyl fauna collected from the 
Mission Valley Formation has been reported by 
Golz (1973) to belong to a stage of evolution 
correlative with the Uinta C. 

The Mission Valley Formation is conformably 
overlain by rocks of the Pomerado Conglomerate 
and no fossils have been found in these rocks. A late 



Eocene age has been assigned to the Pomerado 
Conglomerate at its type locality on the basis of its 
superpositional and gradational relationship with 
the underlying fossiliferous Mission Valley For- 
mation at its type locality. 

The biostratigraphic relationship between fossil 
mollusks, calcareous nannoplankton, Foraminifera, 
and mammals with respect to the lithostratigraphy 
of the Eocene San Diego embayment is illustrated in 
figure 6. As discussed in the preceding pages, each 
of the fossil localities shown in figure 6 is a com- 
posite of many field localities that occur at or very 
near the same stratigraphic horizon. These com- 
posite localities have been plotted with respect to 
their relative vertical and horizontal stratigraphic 
position within the lithostratigraphic regime. The 
boundaries and postulated interrelationships of the 
West Coast (California) Marine Stages. European 
Stages, Epochs, Series, and absolute (radiometric) 
time scale in millions of years are also shown. 

Composite mollusk locality M5 and composite 
mammal locality V2 lie within a few meters of the 
same stratigraphic level and are considered to be 
correlative in age. The molluscan fauna belongs to 
the "Transition Stage" and the mammalian fauna to 
the Uinta B Mammal Age of North America. 
Similarly, composite mollusk locality M6 and mam- 
mal locality V4 lie at the same stratigraphic interval. 
These are Tejon and Uinta C in age respectively. 
Givens (1974) has correlated the Tejon Stage of the 
southern California Ventura Basin with the upper 
Eocene of Europe, on the basis of species also 
reported here from composite locality M6. The 
calcareous nannoplankton from composite locality 
N3 which lies at the same stratigraphic interval as 
locality M6, are also suggestive of a late Eocene age. 

Calcareous nannoplankton from composite 
fossil locality Nl within the middle part of the Ar- 
dath Shale have been correlated with the Discoasier 
siiblodoensis zone (Bukry and Kennedy, 1969). The 
flora of this zone has previously been reported from 
the Canoas Siltstone Member of the Kreyenhagen 
Formation on Garza Creek near Oil City, California; 
from the middle Lutetian strata at Gibret, France; 
and from the Lutetian strata of the Paris basin in 
France (Bouche, 1962). 

The fossil molluscan assemblage collected from 
composite locality M5 is indicative of the "Tran- 
sition Stage". Givens (1974) has shown that the 
"Transition Stage" of southern California, as 
originally defined by Clark and Vokes (1936), 
overlaps the middle-upper Eocene boundary as 
established in the same strata by planktonic 
correlations with type Eocene strata in Europe. 

Composite locality V2 also lies at the same 
stratigraphic interval at locality M5 and is therefore 
considered to likewise lie near the middle upper 
Eocene boundary. The fossils from composite 
localities F2 and N2 are stratigraphically higher 
than those from localities M5 and V2 and are con- 
sidered to he from rocks that are at least late middle 
Eocene age. The fossils from composite localities 
M3, VI , and Fl lie at the same stratigraphic interval 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



29 



as those from Nl and are, therefore, also middle 
Eocene in age. 

In conclusion, composite localities N3, M6, and 
V4 lie within the Mission Valley Formation and are 
late Eocene in age. Composite localities Nl, M3, 
Fl , and VI lie within the Ardath Shale and are mid- 
dle Eocene in age. The boundary between the mid- 
dle and late Eocene lies intermediate between these 
two units within parts of the Scripps Formation, 
Friars Formation, and Stadium Conglomerate. 



POST-EOCENE DEPOSITS 
Miocene 

Andesite Dike 

An andesite dike is located approximately 600 m 
north of the Scripps Institution of Oceanography 
pier(plate 2A).The rock is black, fine grained, and 
has flow structures and columnar joints. The dike 
strikes approximately N. 45° E., but its intersection 
with Eocene rock in the sea cliff cannot be seen. The 
dike has been observed by scuba diving to extend 
from the beach directly beneath the U.S. Fishery 
Oceanography Center for a distance of ap- 
proximately 400 m to the southwest (W. Reetz, per- 
sonal communication, 1971). A whole-rock 
potassium-argon analysis of this rock, which shows 
some evidence of wall-rock assimilation, gave an age 
of 10.9±1.1 million years (J.W. Hawkins, personal 
communication, 1970). 



Pliocene and Pleistocene 

Pliocene and Pleistocene rocks include marine 
sandstone and conglomerate of the upper Pliocene 
San Diego Formation, marine and nonmarine sand- 
stone of the lower Pleistocene Lindavista For- 
mation, and lagoonal and nonmarine sandstone of 
the upper Pleistocene Bay Point Formation. 

San Diego Fornnation 

The San Diego Formation (Dall, 1898) is mid- 
dle or late Pliocene in age (Hertlein and Grant, 
1 944; Cleveland, 1 960). It crops out from the lower 
south-facing slopes of Mount Soledad at Pacific 
Beach south to near San Diego Civic Center and 
along the north-facing slopes of Mission Valley 
from near Old Town to the eastern boundary of the 
area. These exposures, attaining a maximum 
thickness of 30 m, are composed of yellowish- 
brown, fine- to medium-grained, poorly indurated 
sandstone. Cobble conglomerate, thin beds of ben- 
tonite, marl, and brown mudstone further charac- 
terize the section. The thickness of the San Diego 
Formation increases markedly to the south, where it 
has been reported to attain a maximum thickness of 
400 m (Hertlein and Grant, 1939). The lower 200 m 
of this section correlates to the south with the 



Miocene-Pliocene Rosarito Beach Formation in 
northern Baja California. The cobble conglomerate 
beds are composed primarily of Poway-type clasts, 
but some beds contain up to 50 percent clasts of 
granitic and meiavolcanic rocks derived from the 
local basement complex. The bentonite is light 
brown, waxy to earthy, expansible, and very soft. 
The San Diego Formation rests unconformably 
on the older pre-Pliocene rocks and is overlain by 
the Lindavista Formation. It is separated from the 
overlying Lindavista Formation in some places by 
an unconformity, but in other places the contact is 
gradational. 

Lindavista Formation 

The Lindavista Formation was named by Hanna 
(1926) for exposures at the Lindavista railroad 
siding in the La Jolla quadrangle (Lat 32° 53' N.; 
Long 1 1 7° 1 r W.). The formation consists of near- 
shore marine and nonmarine sediments deposited 
on a 10 kilometer-wide wave-cut platform (Lin- 
davista Terrace of Hanna, 1926) following the 
deposition of the middle or late Pliocene San Diego 
Formation (Hertlein and Grant, 1944) and prior to 
the deposition of the fossiliferous late Pleistocene 
(Sangamon) Bay Point Formation (Kern, 1971). A 
molluscan fauna from the Lindavista Formation, in- 
cluding the extinct species Pecten bellus. not known 
from the late Pleistocene, suggests an early 
Pleistocene or late Pliocene age for these rocks (G. 
Kennedy, 1973). The Lindavista Formation is 
predominantly composed of moderate reddish- 
brown interbedded sandstone and conglomerate. 
Ferruginous cement, mainly hematite, gives the Lin- 
davista Formation its characteristic color and a 
resistant nature. 

Both the coarse-grained and fine-grained rocks 
of the Lindavista Formation have been largely 
derived from the older sedimentary rocks within the 
San Diego embayment. Where iron staining, so com- 
mon to the Lindavista Formation, extends down- 
ward into the underlying Eocene rocks, the two 
become difficult to differentiate. 



Bay Point Fornnation 

The Bay Point Formation (Hertlein and Grant, 
1939) is widespread and well exposed in the area 
adjacent to the present-day coastline. It is composed 
mostly of marine and nonmarine, poorly con- 
solidated, fine- and medium-grained, pale brown, 
fossiliferous sandstone. 

The fossils found occur between and 30 m 
above mean high tide and include mollusks, 
Foraminifera, and ostracods. These together in- 
dicate a brackish water estuarine depositional en- 
vironment and a late Pleistocene (Sangamon) age 
(Kern, 1971). 

The marine part of the Bay Point Formation in- 
terfingers with unfossiliferous sandstone that lies 
generally more than 30 m but less than 60 m above 
sea level. This part of the Bay Point Formation is 
considered to be nonmarine slope wash; however, it 
has not been differentiated on the geologic map. 



30 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



Pleistocene and Holocene 
Surficial Deposits 

The Pleistocene and Holocene surficial 
deposits are detrital materials which include 
stream-terrace, landslide, alluvium, slope wash, and 
beach deposits and artificially compacted fill. 

Stream-Terrace Deposits 

Stream-terrace deposits occur very locally as 
thin veneer along the larger drainage courses. The 
deposits include unconsolidated sand and gravel 
derived from older sedimentary, igneous, and 
metamorphic rocks. 

I Landslide Deposits 

The study area is underlain in large part by in- 
competent sedimentary rocks which have been 
broadly dissected by shallow westward-flowing 
stream channels. Most of the landslides in the map 
area are rotational slumps and have occurred along 
valley walls where rocks of the Delmar, Friars, and 
Mission Valley Formations crop out. 

Slope stability with respect to potential land- 
sliding is dependent on several factors: (1) the 
strength of the rock material, (2) the slope angle, (3) 
the degree to which planar surfaces, such as bed- 
ding, joint, and fault planes, are dipping out of the 
slope, (4) the susceptibility of the slope-forming 
materials to saturation by water, which is related to 
the water source, permeability, porosity, and con- 
ditions of drainage. 

The landslides are gravity slides resulting from 
basal erosion of oversieepened slopes, ground water 
saturation, surface-water erosion, and poorly con- 
solidated rock. Sliding has generally occurred along 
a multiple slip surface associated with expansible 
clay The slides have consistently maintained in- 
ternal homogeneity, and rotation of the slide mass is 
normally less than five degrees. Subsurface 
examination of these slides was beyond the scope of 
this study. 

Most of the stream channels that dissect the 
soft sedimentary cover are strongly asymmetrical 
with their steep side exposed to the north. The 
north-facing slopes commonly stand 10 to 15 
degrees steeper than the south-facing ones, which 
seldom reach angles greater than 30 degrees. Over- 
steepening of the stream channels is controlled in 
part by the presence of resistant impermeable rock 
layers exposed along the upper slopes as erosional 
ledges and platforms. The ledges protect the softer 
incompetent material below from direct rainfall but 
not from stream erosion. Landslides occur beneath 
the resistant conglomerate within incompetent rock 
as a result of undercutting by adjacent streams. 

Several man-induced slides investigated during 
this study were found to occur beneath resistant 
conglomerate layers and within soft sandstone and 
claystone of the Delmar, Friars, and Mission Valley 
Formations just as in most of the natural slides. 
Stability filling (compacted till placed over a ben- 
ched cut slope) may be one means by which this type 



of failure can be avoided. Landslide incidence in the 
area is greatly increased during periods of high an- 
nual rainfall; good subdrainage may be another 
means of control. During periods of high 
precipitation, the saturation of bedrock may result 
in the lowering of the internal strength of perhaps 
already weak rock. Removal of slope-supporting 
material might then increase landslide potential. 

The landslide deposits of the area can be sub- 
divided into tlve major groups based on lithology 
and genesis. These are (1 )rotational slump deposits 
associated with the shallow stream channels un- 
derlain by sedimentary rocks of Eocene age (photo 
3);(2)rotational slump deposits associated with the 
sea cliffs underlain by sedimentary rocks of Eocene 
age north of the Rose Canyon fault zone (photo 4); 
(3) rotational slump deposits associated with 
sedimentary rocks of Upper Cretaceous and Eocene 
age within the Rose Canyon fault zone (photo 5);(4) 
rotational slump deposits associated with sedimen- 
tary rocks of Upper Cretaceous age on the east- 
facing slopes of the Point Loma Peninsula (photos 6 




Photo 3. A small slump that has occurred within the Ardath 
Shale as a result of slope undercutting and incompetent rocks, 
looking southeast. 



**'Z'A 




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-"^i:- 



m 



Photo 4. Torrey Pines State Park landslide, looking east. The 
landslide is located 2400 meters south ol Soledad Valley in the 
sea cliffs. The slide mass is composed of incompetent rocks 
that are of Eocene age and belong to the Delmar Formation, 
Torrey Sandstone, and Ardath Shale. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



31 



and 7); (5) rockfall deposits associated with 
sedimentary rocks of Upper Cretaceous and 
Pleistocene age in the sea cliffs between the Rose 
Canyon fault zone and the tip of Point Loma Penin- 
sula (photo 8; Kennedy, 1973b). 

Eighteen clay samples were collected from for- 
mations that have high landslide incidence. These 
samples were analyzed for their particle size 
distribution, clay mineral content, and Atterberg 
limits. 

Table 1 presents the results of the Atterberg 
tests and the quantity of the individual size fractions 
from the particle size distribution tests. 

For engineering purposes the clay fraction is 
defined as less than 0.002 millimeter (mm), the silt 
fraction from 0.002 to 0.074 mm, and the sand frac- 
tion from 0.074 to 2.0 millimeters. The liquid limit 
(LL) is defined as the minimum moisture content at 
which the material behaves as a liquid using this 
lest. The plastic limit (PL) is defined as the 
minimum moisture content at which the sample 
behaves plastically using this specified test 
procedure. The plasticity index (PI) is the numerical 
difference between the liquid limit and the plastic 
limit. The plasticity index is then the range of 
moisture content over which the sample behaves 
plastically. There exists a direct relationship bet- 
ween the liquid limit and "compression index," and 
between the liquid limit and the "coefficient of con- 
solidation" (Terzaghi and Peck, 1968), whereas an 
inverse relationship exists between the plasticity in- 
dex and "shear resistance." 



TRACE OF THE MOUNT SOLEDAD FAULT 



LANDSLIDE 
" DEPOSITS 




The stated median particle size was taken from 
ihe 50 percent cumulative level of particle size 
distribution graphs. The arithmetic mean of the 
median particle sizes among all the samples is 0.016 
mm (16 microns), which is in the lower portion of 
the silt range. 

Associations between plasticity index, particle 
size, and the percentage of clay-sized particles are 
readily observed from the data of table 1. The 
medium-plasticity samples (PI = 10 to 20) have an 
average median particle size of 47 microns. High- 
plasticity samples (PI = 20 to 40) have an average 
median particle size of 14 microns. The very-high- 
plasticity samples (PI > 40) have a mean particle 
size of 6 microns. 

Most landslides have occurred in rocks that 
have a plasticity index greater than 20. Surficial 
slumping of slopes underlain by rocks of the Delmar 
and Friars Formations and Ardath Shale is most 
abundant where the plasticity index is greater than 
35. Expansion cracks are especially well developed 
and up to 50 centimeters (cm) deep and 5-10 cm 
wide in much of the area underlain by the Delmar 
and Friars Formations where the plastic index is 
greater than 40. 




Photo 6. Ancient landslide deposits underlain by rocks of the 
Upper Cretaceous Rosarlo Group on Point Loma Peninsula, 
looking west. 



FORT ROSECRANS LANDSLIDES 




Photo 5. Landslides that have occurred as a result of 
oversteepened slopes associated with an erosional 
scarp, looking southeast along the Mount Soledad fault. 



Photo 7. Fort Rosecrans landslide on Point Loma Peninsula, 
looking west. This slide mass Is presently moving toward the 
east at a rate of approximately 10 centimeters per year. 



32 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 






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GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



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300 m south of locality C-7 in road cut on west 
side of Black Mountain Road, 1 m above road 
level; lat. 32° 56' 50" N., long. 117° 07' 43" W.; 
Delmar and Friars Formations undifferen- 
tiated; fairly broad 15 a with very diffused 25- 
35 A line. 

215 m south of locality C-8 in road cut on west 
side of Black Mountain Road at road level; 
lat. 32° 56' 42" N., long. 117° 07' 42" W.; Del- 
mar and Friars Formations undifferentiated; 
low intensity, broad 15° a plus high back- 
ground 2O-40a. 

ISO m east of intersection between Coast High- 
way 101 and Carmel Valley Road on north side 
of road cut, 2 m above road level; lat. 32° 56' 
23" N., long. 117° 15' 32" W.; Delmar Forma- 
tion; extremely low, broad 12.5a line; mostly 
x-ray amorphous (allophane). 

120 m east of sea-cliff-stairway in northern part 
of Torrey Pines State Park on south side of 
road leading from stairway to park headquar- 
ters, 2 m above road level in high north facing 
cut; lat. 32° 55' 34" N., long. 117° 15' 25" W.; 
Delmar Formation; no line detected; x-ray 
amorphous (allophane). 

900 m south of Carmel Valley Road on Sorrento 
Valley Road in west facing road cut, 2 m above 
road level; lat. 32° 55' 16" N., long. 117° 14' 
17" W.; Delmar Formation; essentially x-ray 
amorphous (allophane). 

First road cut for Interstate Highway 5 north of 
Penasquitos Valley, 1 m above highway level 
and 15 m north of the southern end of the cut; 
lat. 32° 54' 30" N., long. 117° 13' 28" W.; 
Ardath Shale. 

35 m north of intersection between Genesee Ave- 
nue and Interstate Highway 5 in road cut 
above onramp for freeway, 1 m above road 
level; lat. 32° S3' 13" N., long. 117° 13' 33" W.; 
Ardath Shale. 




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34 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 







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1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



35 




Photo 8. Sunset Cliffs located on tfie northern part of the Point Loma Peninsula, looking east. The arcuate coastline develop- 
ment here is the result of rockfall landsliding. 



Alluvium and Slope Wash 

Alluvium consists primarily of poorly con- 
solidated stream deposits of silt, sand, and cobble- 
sized particles derived from bedrock sources that lie 
within or near the area. These deposits intertongue 
with Holocene slope wash that commonly mantles 
the lower valley slopes throughout coastal San 
Diego County. Alluvium and slope wash are mostly 
undifferentiated on the geologic maps. 

Slope wash deposits are poorly cc.isolidated 
surficial materials derived chiefly from nearby soil 
and decomposed bedrock sources. The slope wash 
is deposited along the flanks of the lower valley 
slopes by the actions of gravity and surface water. 
Thick deposits of slope wash are especially common 
on the Delmar Formation, Ardath Shale, Scripps 
Formation, and Friars Formation where deep soil 
horizons have developed. Expansive clay materials 
deposited as slope wash yield the hummocky 
topography developed on rocks of lagoonal and non- 
marine origin. 

Beach Deposits 

The beach deposits are composed of un- 
consolidated sand and silt. They mantle those parts 
of the present day sea coast where erosional con- 
ditions are slow. They are derived from many sour- 
ces as a result of longshore drift and alluvial 
discharge from the major stream courses. 



Artificially Compacted Fill 

Artificial fill consists of artificially compacted 
earth materials derived from many sources. Only 
large areas underlain by artificial fill have been 
delineated on the geologic maps. 



STRUCTURE 
AND SEISMIC HISTORY 

r-- 

I Faults in the San Diego coasial area lie within a 

regional northwest-striking right-lateral fault system 
j that includes the active Mission Creek, San An- 
I dreas, San Jacinto, and Elsinore fault zones to the 
east and the Agua Blanca, San Clemente, and Ram- 
part fault zones to the west. Within the study area 
the faults comprise two prominent sets. One set 
strikes parallel to the regional grain, whereas the 
other set strikes northeast. Faults belonging to both 
of these sets have displaced rocks of the late 
Pleistocene Bay Point Formation which has, on the 
basis of a rich nearshore molluscan fauna, been 
assigned an age of approximately 100,000 years 
(Kern, 1971). 

The most prominent faults within the northwest 
striking set belong to the Rose Canyon fault zone. 



36 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



These faults juxtapose nearly flat-lying Eocene, 
Pliocene, and Pleistocene rocks with steeply tilted 
Upper Cretaceous and Eocene rocks. The Rose 
Canyon fault has been considered a southern ex- 
tension of the Nevvport-Inglewood fault zone 
(Corey, 1954; Emery, 1960; King, 1969; Moore, 
1972) and a northern extension of both the Los 
Buenos and the San Miguel faults (Wiegand, 1970; 
Moore and Kennedy, 1970; Moore, 1972). If the 
Rose Canyon-Los Buenos fault zone is continuous, 
it has an onshore length of 65 km and extends from 
La Jolla on the north to near El Rosarila in northern 
Baja California on the south. If the Rose Canyon 
fault zone is continuous with the San Miguel fault, 
the onshore length of this segment is over 250 km 
and extends from La Jolla on the north to near San 
Miguel in northern Baja California on the south. 
The mapped northern offshore extension of the 
Rose Canyon fault zone extends from La Jolla to 
within 45 km of the southern onshore termination of 
the Newport-Inglewood fault zone (Moore, 1972). 
Point Loma and Mount Soledad are fault blocks that 
were uplifted along the Rose Canyon fault zone in 
part after the deposition of the Lindavista For- 
mation. At least 135 m of vertical separation can be 
measured in the vicinity of Mount Soledad and La 
Jolla (plate 2A). The direction of the vertical 
movement at La Jolla is west side up, whereas at 
Mission Bay it is west side down (sections B-B', C- 
C). At least 1 00 m of separation has been shown on 
the Rose Canyon fault zone in the Mission Bay area 
with the west side down (Peterson, 1970). Possibly 
the Mount Soledad block rotated along an axis nor- 
mal to the strike of the fault zone thereby elevating 
Mount Soledad along the northwest side of the zone 
and sinking Mission Bay along the southwest side. 
This tilted block model is supported by the fact that 
a 30 m high wave-cut platform upon which the Lin- 
davista Formation originally was deposited, on the 
south-facing slopes of Mount Soledad, is inclined to 
the south and extends nearly continuously from an 
elevation of over 250 m at the north to near sea level 
at the south. 

Steep folds associated with the nor- 
theasternmost part of the Mount Soledad block (sec- 
tion B-B') are considered to be in part the result of 
compression developed by strike-slip movement. 
The rotation of Mount Soledad was questionably 
caused by flexure associated with the change in 
strike of the Rose Canyon and Mount Soledad faults 
between LaJollaCove and Rose Canyon (plate 2A). 
The Tertiary and younger rocks that lie immediately 
west of the fault zone are not deformed and they 
make a strike-slip model and compressional folding 
logical. It has been suggested that the Rose Canyon 
fault is part of a regional right-lateral strike-slip 
fault system. The distribution of the San Diego For- 
mation along the Rose Canyon fault zone between 
Pacific Beach and Tecolote Canyon(plate 2A) is in- 
terpreted as resulting from 4 km of right-lateral 
strike-slip motion on the Rose Canyon fault. 
Horizontal slickensides measured on the Rose 
Canyon fault at La Jolla and Mount Soledad further 
suggest strike-slip faulting. 



In the northern coastal part of the area at 
Torrey Pines State Park and in the southern part of 
the area at Point Loma, the structural grain of the 
area is nearly perpendicular to the Rose Canyon 
fault zone. The average strike of the grain is 30 to 
40 degrees east of north. The separation along most 
of the faults is vertical and ranges from 1 cm to 100 
m. 

Several northeast striking faults displace 
Pleistocene and younger(?) deposits. The Carmel 
Valley fault south of Del Mar (plate lA) has ap- 
proximately 2 m of vertical separation, involving the 
Lindavista Formation at lat 32° 55' 10" N.; long 
117° 14' 50" W. Along this same fault at lat 32° 55' 
20" N.; long 117° 14' 50" W., the late Pleistocene 
Bay Point Formation has been tilted approximately 
10 degrees. It is speculated, however, that at least 
part of this dip is initial and related to its 
deposition. A small fault on the east side of the 
Point Loma Peninsula, located at lat 32° 40' 40" N.; 
long 1 17° 14' 15" W., also displaces rocks of the 
Bay Point Formation. The separation on this fault is 
dip-slip and on the order of 3 meters. The Bay Point 
Formation is also faulted by a small northeast 
striking fault that intersects the Point Loma fault at 
an oblique angle(plate3A).The vertical separation of 
the Bay Point Formation related to this fault and the 
Point Loma fault together is in excess of 30 meters. 

The possibility of Holocene fault activity in the 
area is not ruled out, though no direct field evidence 
supports this fact. Holocene faulting is indirectly 
postulated by the fact that historic seismicity might 
be related to faulting on the Rose Canyon fault zone 
in the San Diego Bay area and by subbottom 
acoustic profiles that show probable Holocene 
sediments offset on the sea floor at a point ap- 
proximately 25 km north of La Jolla along the trace 
of the Rose Canyon fault (Moore. 1972). 

Forty-four earthquakes of Richter magnitude 
2.5 to 3.7 (M 2.5-3.7) have been recorded within the 
greater San Diego area by the California Institute of 
Technology Seismological Laboratory since 1950. 
Three of these which occurred in the vicinity of San 
Diego BayonJune21 and22andJuly 14, 1964, had 
epicenter localities within a few kilometers of San 
Diego and magnitudes of 3.7, 3.6, and 3.5, respec- 
tively. 

In addition to earthquakes originating in the San 
Diego area, ground shaking has been felt there 
initiated by earthquakes that have had epicenters up 
to 100 km away. Several of these earthquakes have 
caused damage in San Diego and are worthy of men- 
tion. 

The 1933 Long Beach earthquake (M 6.6) 
caused minor damage throughout northwestern San 
Diego County and was felt sharply as far south as 
San Diego. The epicenter is shown by the California 
Institute of Technology Seismological Laboratory to 
have been south of Long Beach along the inferred 
trace of the Newport-Inglewood fault zone. 

On November 4, 1949. and on February 9, 
1956, earthquakes felt sharply in San Diego oc- 
curred on the Valecitos-San Miguel fault in northern 
Baja California. The 1949 earthquake (M 5.7) had 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



37 



an epicentral distance of approximately 75 km 
southeast of the San Diego Civic Center. The 
epicenter of the 1956 earthquake (M 6.8) was ap- 
proximately 1 75 km south of San Diego. Three af- 
tershocks of this earthquake, with magnitudes 
greater than 6, occurred in 1956 on February 9, 14, 
and 15. Ground rupture of 20 km was associated 
with this earthquake in the vicinity of the epicenter 
(Shor and Roberts, 1958). 

Several earthquakes (M > 5) have been recor- 
ded on the Agua Blanca fault in northern Baja 
California during the past 30 years with epicentral 
distances within 125 km of San Diego. Holocene 
fault scarps in the area between Ensenada and Santo 
Tomas suggest surface rupture has occurred in at 
least the past few thousand years. 

During the past 35 years, earthquakes located 
in the Imperial Valley and Salton Trough area were 
felt in western San Diego County. Three of 



these — the 1940 Imperial Valley earthquake (M 
7.1), the 1951 Superstition Hills earthquake (M 
5.6), and the 1968 Borrego Mountain earthquake (M 
6.5) — caused minor damage to structures in the San 
Diego coastal area and initiated landsliding of sea 
cliff property at Point Loma, La Jolla, and Torrey 
Pines State Park (Kennedy, 1973). 

The February 9, 1971, San Fernando earth- 
quake (M 6.4) was felt sharply throughout the 
southern California coastal area. The intensity of 
the earthquake at San Diego was V (Scott, 1971 ) on 
the Modified Mercalli scale. Minor damage was 
reported as far south as the Mexican border, and 
two small landslides occurred at Sunset Cliffs as a 
direct result of the initial shock. 

Allen et al. (1965) show a strain release ofO.25 
to 4 (M 3) earthquakes/100 km2 for the 29-year 
period between 1934 and 1963 for the San Diego 
area. 



38 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



REFERENCES CITED 



Allen. C.R.. et al., 1965, Relationship between selsmlclty and 
geologic structure In the southern Calitornia region: 
Seismologlcal Soc of America Bull., v. 55, no. 4, p. 753-797. 

Allison. E.C.. 1964. Geology o( areas bordering Gulf of Califor- 
nia: American Assoc. Petroleum Geologists f^em 3, p. 3- 
29. 

Beal. CM.. 1924, Informe sobre la exploracion geologica de la 
Baja California: Boletin Petroleo. v. 17, p. 417-473. 

Berggren, W.A., 1969, Rates of evolution in some Cenozoic 
planktonic Foraminifera: Micropaleo, v. 15, no. 3. 

Bouche, P.M., 1962. Nannofossiles calcaires du Lutetien du 
bassin de Paris: Rev. f\^icropaleontologie, v 5. p. 75-103. 

Bukry. David, and Kennedy. MP.. 1969, Cretaceous and Eocene 
coccoliths at San Diego. California, in Short contributions to 
California geology California Division of Mines and Geology 
Special Report 100, p. 33-43. 

Bushee, J., Holden, J., Geyer, B., and Gastil, G., 1963, Lead- 
alpha dates for some basement rocks of southwestern 
California: Geol. Soc. America Bull., v. 74. p. 803-806. 

Clark. B.L.. and Vokes, HE.. 1936, Summary of marine Eocene 
sequence of western North America: Geol. Soc. America 
Bull.. V. 47. p. 851-876, 2 pIs., 3 figs. 

Cleveland. G.B.. 1960. Geology of the Otay clay deposit, San 
Diego County, California: California Div. Mines Spec. Rept. 
64, p. 16. 

Corey, W.H., 1954. Tertiary basins of southern California, in 
Geol. of southern California: California Div. Mines Bull. 170, 
chpt. 3, p. 73-83. 



Dall, W.H., 1898, 18th Ann. Rept. 
correlation table opp. p. 334. 



U.S. Geol. Survey, pt. 2. 



DeLisle, M., Morgan. J, R., Heldenbrand, J., and Gastil, G., 1965, 
Lead-alpha ages and possible sources of metavolcanic 
rock clasts in the Poway Conglomerate, southwest Califor- 
nia: Geol. Soc. America Bull., v. 76, p. 1069-1074. 

Ellis. A.J.. 1919, Geology, western part of San Diego County, 
California: U.S. Geol. Survey Water-Supply Paper 446, p. 50- 
76. 

Emery. K.O.. 1960, The sea off southern California, a modern 
habitat of petroleum; New York, London, John Wiley, 366 p., 

map. 

Evernden, J,F.. and Kistler. R.W.. 1970, Chronology of em- 
placement of Mesozoic batholithic complexes in California 
and western Nevada: U.S. Geol. Survey Prof. Paper 623. 42 
P 

Fife, D.L., Minch, J. A., and Crampton. P.J., 1967, Late Jurassic 
Age of the Santiago Peak Volcanics, California: Geol. Soc. 
America Bull., v. 78, p. 299-304. 

Flynn, C.J . 1970. Post-batholithic geology of the La Gloria- 
Press Rodriguez area, Baja California, Mexico: Geol. Soc. 
America Bull., v. 81, p. 1789-1806. 

Givens, C.R., 1974, Eocene Molluscan biostratigraphy of the 
Pine Mountain area, Ventura County, California: University 
of California, Dept. Geol. Sci. Bull., v. 109. 107 p. 

Golz, D.J., 1971, SelenodonI Artiodactyls from the Eocene of 
southern California: Geol Soc. America Abstracts with 
Program, v. 6, p. 125. 

Golz, D.J., 1973, The Eocene Artiodactyla of southern Califor- 
nia: Unpublished Ph.D. dissertation. University of Califor- 
nia, Riverside 



Golz, D.J., and Kennedy, MP. 1971, Comparison of Mammalian 
and Invertebrate Chronologies in the Eocene of southern 
California: Geol. Soc. America Abstracts with Program, v 
6. p. 125. 

Gray, C.H., Jr . Kennedy, MP., and Morton, P K., 1971, Petroleum 
potential of southern coastal and mountain area, Califor- 
nia: American Assoc Petroleum Geologists, Mem. 15, p. 
372-383. 

Hanna. M.A., 1926, Geology of the La Jolla quadrangle, Califor- 
nia: University of California, Dept. Geol. Sci. Bull., v. 16, p. 
187-246. 

Hertlein, L.G., and Grant. U.S.. IV, 1939. Geology and oil 
possibilities of southwestern San Diego County: California 
Jour Mines and Geol., v. 35, p. 57-78. 

Hertlein, L.G., and Grant, U.S., IV, 1944, The geology and 
paleontology of the marine Pliocene of San Diego, Califor- 
nia, pt. 1, Geology: San Diego Soc. Nat History Mem., v 2, 
p. 1-72. 

Jenkins, D.G , 1965. Planktonic Foraminiferal Zones and New 
Taxa from the Danian to lower Miocene of New Zealand: 
New Zealand Jour. Geol. Geophys., v. 8, p. 1088-1126. 

Kennedy, G.L., 1973, Early Pleistocene Invertebrate Faunule 
from the Lindavista Formation, San Diego, California: San 
Diego Soc. Nat. History Transactions, v. 17, p. 119-128. 

Kennedy, M.P., 1967, Preliminary report, engineering geology of 
the city of San Diego, California: California Div. of Mines 
and Geology open tile, 21 p., 3 maps, scale 1:24,000. 

Kennedy. MP. 1969, Preliminary geologic maps of portions of 
San Diego city. California: California Division of Mines and 
Geology open file reports 69-1 (Del Mar sheet). 68-10 (Del 
Mar - La Jolla sheet), 69-13 (La Jolla - Point Loma sheet), 
69-14 (Point Loma sheet), scale 1:9,6000. 

Kennedy. MP.. 1971, Eocene shoreline fades in the San Diego 
coastal area, California: Geol, Soc. America Abstracts with 
Program, v. 6 p. 142. 

Kennedy, MP., 1973a, Stratigraphy of the San Diego em- 
bayment, California: Unpublished Ph.D. dissertation, 
University of California, Riverside. 

Kennedy, MP., 1973b, Sea cliff erosion at Sunset Cliffs, San 
Diego, California: California Div. Mines and Geology, 
California Geology, v. 26, p. 27-31. 

Kennedy, M.P., and Moore, G.W., 1971a, Stratigraphic relations 
of upper Cretaceous and Eocene formations, San Diego 
coastal area, California: American Assoc. Petroleum 
Geologists Bull., v. 55, p. 709-722. 

Kennedy. MP., and Moore, G.W.. 1971b. Stratigraphy and struc- 
ture of the area between Oceanside and San Diego, 
California: geologic road log, in Elders W.A.. ed., 1971, 
Geological excursions in southern California: Geol. Soc, 
America Cordilleran Section Meeting, Riverside, California, 
field trip guidebook. 

Kennedy, MP., and Peterson, G.L., 1975, Geology of the La 
Mesa, Poway. and SW 1/4 Escondido quadrangles, eastern 
San Diego metropolitan area, California: California Div. 
Mines and Geology Bull. 200B. 

Kern, J. P., 1971, Paleoenvironmental analysis of a late 
Pleistocene estuary in southern California: Journal Paleo.. 
V. 45, p. 810-823. 

King, P.B., 1969. The tectonics of North America: U.S. Geol. 
Survey Prof Paper 628, 94 p., map scale 1:5,000,000. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



39 



Larsen, E.S., 1948, Batholith and associated rocks of Corona, 
Elsinore, and San Luis Rey quadrangles, southern Califor- 
nia: Geol. Soc. America Mem. 29, 182 p. 

Mallory, V.S., 1959, Lower Tertiary biostratigrapfiy of the 
California coast ranges: American Assoc, Petrol. Geol., 
297 p. 

Merriam, R., 1968, Geologic reconnaissance of northwest 
Sonora: Stanford University Pub. Geol. Sci., v. 11, p. 287. 

Milow, E.D., and Ennis, D.B., 1961, Guide to geologic field trip of 
southwestern San Diego County: Geol. Soc. America, Cor- 
dilleran Sec, 57th Ann. Mtg., Guidebook, p. 23-43. 

Minch, J.A., 1967, Stratigraphy and structure of the Tijuana- 
Rosarito Beach area, northwestern Baja California, 
Mexico: Geol. Soc. America Bull., v. 78, p. 1155-1178. 

Minch, J. A., 1972, The late Mesozoic-early Tertiary framework of 
continental sedimentation, northern Peninsular Ranges, 
Baja California, Mexico: Unpublished Ph.D. dissertation. 
University of California, Riverside. 

Moore, E.J., 1968, Fossil mollusks of San Diego County: San 
Diego Soc. Nat. History Occasional Paper 15, 76 p. 

Moore, G. W., 1972, Offshore extension of the Rose Canyon 
fault, San Diego, California: U.S. Geol. Survey Prof. Paper 
800-C. p. C113-C116. 

Moore, G.W., and Kennedy, M.P., 1970, Coastal geology of the 
California — Baja California border area: American Assoc. 
Petroleum Geologists Guidebook, Pacific Sections, fall 
field trip p. 4-9. 

Morton, P.K., 1972, Geologic guidebook to the northern Penin- 
sularRanges, Orange and Riverside Counties, Califomia: 
Prepared jointly by National Assoc, of Geol. Teachers and 
South Coast Geological Soc, for N.A.G.T. far western sec- 
tion meeting, Chapman College, Orange, California. 

Nordstrom, C.W., 1970, Lusardi Formation— a post-batholithic 
Cretaceous conglomerate north of San Diego, Califomia: 
Geol. Soc. America Bull., v. 81, p. 601-605. 

Peterson, G.L., 1970, Quaterlnlary deformation of the San Diego 
area, southwestern Califomia: American Assoc. Petroleum 
Geologists Guidebook, Pacific Section, fall field trip, p. 
120-126. 

Peterson, G.L., and Kennedy, M.P., 1974, Lithostratigraphic 
variations in the Poway Group near San Diego, Califomia: 
San Diego Soc. Nat. History Transactions, v. 17, p. 251-258. 

Peterson, G.L., and Nordstrom, C.E., 1970, Sub-La Jolla un- 
conformity in the vicinity of San Diego, California: 
American Assoc. Petroleum Geologists Bull., v. 54, p. 256- 
274. 



Popenoe, W.P,. Imlay, R.W., and Murphy, M.A., 1960, Correlation 
of the Cretaceous formations of the Pacific coast (United 
States and northwestern Mexico): Geol. Soc America Bull., 
V. 71, p. 1491-1540. 

Scott, N.H., 1971, Preliminary report on felt area and intensity, 
In The San Fernando, California, earthquake of February 9, 
1971: U.S. Geol. Survey Prof. Paper 733, p. 153-154. 

Sears, J.D., Hunt, C.B , and Hendricks, T.A., 1941, Tran- 
sgressive and regressive Cretaceous deposits in southern 
San Juan Basin, New Mexico: U.S. Geol. Survey Prof. Paper 
193-F, p. 100-121. 

Shor, G.G., and Roberts, E., 1958. San Miguel, Baja California 
Norte, earthquakes of February. 1956: a field report: 
Seismological Society of America Bull., v. 48, p. 101-116. 

Slitter, W.V., 1968, Upper Cretaceous Foraminifera from 
southern California and northwestern Baja California, 
Mexico: The University of Kansas Pubs.. Art. 7, Ser. no. 49, 
p. 141. 

Steineck, P.L., and Gibson, J.M., 1971, Age and correlation of 
the Eocene Ulatisian and Narizian stages, California: 
Geol. Soc. America Bull., v. 82, p. 477-480. 

Strand, R.G., 1961. Geologic map of California — San Diego-El 
Centre sheet: California Div. Mines and Geology. 

Terzaghi, K., and Peck, R.B., 1967, Soil mechanics in 
engineering practice: Wiley and Son, New York, 729 p. 

Turner, H.C., Ebert, E.E., and Given, R.R., 1968, The Marine en- 
vironment offshore from Point Loma. San Diego County: 
California Department of Fish and Game. Fish Bull. 140. 

Weber, F.H., Jr., 1963, Geology and mineral resources of San 
Diego County, Califomia: California Div. Mines and 
Geology County Rept. 3, 309 p. 

Wiegand, J.W., 1970, Evidence of a San Diego Bay-Tijuana 
fault: Assoc, of Engineering Geologists Bull., v. 7, p. 107- 
121. 



Wood, H.E., Chaney, R.W., Clark, J., Colbert. E.H.. Jepsen, G.L.. 
Reeside, J.B.. Jr., and Stock, C., 1941, Nomenclature and 
correlation of the North American Continental Tertiary: 
Geol. Soc. America Bull., v. 52, p. 1-48. 

Woodford, A.O., Welday, E.E., and Merriam, R., 1968. Siliceous 
tuff clasts in the upper Paleogene of southern California: 
Geol. Soc. America Bull., v. 79, p. 1461-1486. 



SECTION B 

La Mesa, Poway, 

and SlVi/4 Escondido 

quadrangles 



ABSTRACT 



The La Mesa, Poway, and SWV4 Escondido 7.5-minute quadrangles cover approximately 380 square 
kilometers (km?) within the eastern and northeastern San Diego metropolitan area. The geology of the 
area consists of two principal rock units: 1) an igneous and metamorphic basement complex and 2) a 
superjacent sedimentary succession of strata. 

The basement complex is composed of the Upper Jurassic Santiago Peak Volcanics, a structurally 
complex, mildly metamorphosed unit composed of andesitic volcanic and volcaniclastic rocks and mid- 
Cretaceous rocks of the southern California batholith. Metamorphism of the Santiago Peak Volcanics, 
emplacement of the batholithic rocks, uplift, and carving of an erosion surface with relief in excess of 500 
meters (m) was completed by Late Cretaceous time. 

The post-batholithic superjacent sedimentary succession was deposited on this high relief erosion 
surface. Mapped stratal units include the Upper Cretaceous Lusardi Formation; the Eocene Friars For- 
mation, Stadium Conglomerate, Mission Valley Formation, and Pomerado Conglomerate; the Pliocene 
San Diego Formation; the Pleistocene Lindavista Formation; and Holocene landslide, alluvial, slope 
wash and stream-terrace deposits. 

The most abundant rocks of the sedimentary succession are middle and upper Eocene fossiliferous 
strata of marine, lagoonal, and nonmarine origin related to two major transgressive and regressive 
depositional episodes. The Lindavista Formation caps the older rocks throughout much of the area and 
was deposited during a marine regressional event following a marine planation. Later uplift of these 
deposits is indicated by the presence of fossiliferous marine strata that now lie at an elevation of 165 m. 
above sea level. 

Seismically the area is quiet; however, it lies within a part of southern California considered to be a 
region of tectonic activity. Forty-four earthquakes of Richter magnitude between 2.5 and 3.7 (M 2.5 to M 
3.7) have been recorded by the California Institute of Technology Seismological Laberatory since 1950 
that have had epicentral localities within the greater San Diego metropolitan area. 

No known Holocene faults exist in the area. However, the Pleistocene Lindavista Formation has been 
faulted in several places. One of these faults lies within the Mission Valley River drainage, south of Mis- 
sion Gorge, where the Lindavista Formation has been offset at least 20 meters. A fault near Collwood 
Boulevard and Montezuma Road in the southern part of the area also cuts rocks of the Lindavista Forma- 
tion and is considered to be a northern branch of the La Nacion fault. 

Sand and gravel deposits useable for concrete, bituminous, and ceramic aggregate underlie a large 
part of the area. Clay deposits useable for ceramics, fire clay, and possibly lightweight aggregate are 
also abundant but have not been exploited. These widespread clay deposits are expansible, and closely 
associated with landslides, especially in those areas directly underlain by the Friars Formation. 

The landslides mapped are rotational slumps that have occurred as the result of incompetent rock, 
saturation, expansible clay, and oversteepened valley slopes. Surficial landslides are associated with 
slopes steeper than 25 degrees that are underlain by rocks of the Friars and Mission Valley Formations 
throughout the area. 



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# 



GEOLOGY OF THE EASTERN SAN DIEGO METROPOLITAN 
AREA, CALIFORNIA 

La Mesa, Poway, and SWV4 Escondido quadrangles 

by Michael P. Kennedy^ and Gary L. Peterson2 



INTRODUCTION 

In 1965 the California Division of Mines and 
Geology, in cooperation with the City of San Diego, 
began a comprehensive geologic investigation of the 
greater San Diego metropolitan area. This report 
deals with the geology of the eastern half of that in- 
vestigation, A similar report has been written on the 
western half and includes the geology of the Del 
Mar, La Jolla, and Point Loma quadrangles (Ken- 
nedy, 1975). 

The La Mesa, Poway, and SW 1/4 Escondido 
quadrangles comprise more than 25 percent of the 
greater San Diego metropolitan area (figure 1 ). This 
area is underlain by San Diego's richest sand, 
gravel, and crushed stone resources, deemed 
feasibly extractable in today's market for use in the 
Mission Valley, Mira Mesa, Poway, and Escondido 
suburbs. These resources and others, including rich 
clay deposits, are being rapidly covered by urban 
development. The clay deposits, which are locally 
expansible, in turn constitute a serious geologic 
hazard to development. 

The geologic mapping and detailed descriptions 
of the rock units are intended to be used as aids in 
planning for land use and future development. The 
stratigraphic relationship between the rock units un- 
derlying the study area and those that underlie the 
area to the west (discussed by Kennedy, 1975) are 
shown in figure 2. 

Previous geologic investigations that have been 
especially useful in this study include a ground 
water investigation by A.J. Ellis (1919), a 
stratigraphic and paleontologic study of the La Jolla 
quadrangle by M.A. Hanna (1926), two papers on 
geology and paleontology of the San Diego area by 
L.G. Hertlein and U.S. Grant IV (1939, 1944), and a 
monograph on the mineral resources of San Diego 
County by F.H. Weber, Jr. (1963). 

The authors would like to extend special thanks 
to D.M. Morton and G.W. Moore of the United 
States Geological Survey for their suggestions and 
contributions pertinent to the results of this study. 
Acknowledgment is due also to M.O. Woodburne, 
P.K. Morton, G.B. Cleveland, F.H. Weber, Jr., C.H. 
Gray, Jr., M.A. Murphy, J. P. Kern, R.G. Strand, and 
Y.H. Smitter for their enthusiastic help, interesting 
discussions, and review of the maps and manuscript. 



PRE-EOCENE DEPOSITS 
Basement Complex 

The basement complex consists of two principal 
rock units: (1) the Upper Jurassic Santiago Peak 
Volcanics, a succession of deformed and metamor- 

■Geologist. Cahlornia Division ol Mines ana Geology 
-San Diego State University 



phosed volcanic, volcaniclastic, and sedimentary 
rocks; and (2) mid-Cretaceous plutonic rocks of the 
southern California batholith, which intrude the 
Santiago Peak Volcanics. 

Santiago Peak Volcanics 

The Santiago Peak Volcanics comprise an 
elongate belt of mildly metamorphosed volcanic, 
volcaniclastic, and sedimentary rocks that crop out 
from the southern edge of the Los Angeles basin 
southward into Mexico (Gray et al., 1971). These 
rocks were mapped in the San Diego area by Hanna 
(1926, p. 199-204) as "Black Mountain Volcanics," 
but that name was pre-empted, and Larsen (1948) 
suggested the substitute--Santiago Peak Volcanics. 

The volcanic rocks range in composition from 
basalt to rhyolite but are predominantly dacite and 
andesite. The succession is typified by a wide 
variety of breccia, agglomerate, volcanic 
conglomerate, and fine-grained tuff-breccia. Highly 
silicified rock (probably tufO and a variety of dark, 
dense, fine-grained hornfels occur locally. To the 
west, some local, thin, fossil-bearing marine 
sedimentary rocks are interbedded with the volcanic 
and volcaniclastic rocks. Included with the Santiago 
Peak Volcanics are a number of small plutons of 
mildly metamorphosed gabbro. These are herein in- 
cluded with the Santiago Peak Volcanics because 
they are metamorphosed and were probably feeders 
for the volcanic rocks rather than parts of the 
batholith. 

The Santiago Peak Volcanics are hard and ex- 
tremely resistant to erosion and form topographic 
highs. Most of the volcanic rocks are dark greenish 
gray where fresh but weather grayish red to dark 
reddish brown. The soil developed on the Santiago 
Peak Volcanics is the color of the weathered rock 
and supports the growth of dense chaparral. 

Within a narrow 2-kilometer-long belt, ap- 
proximately I km northwest of Rancho Bernardo in 
the Escondidoquadrangle(plate IB), a succession of 
low-grade metamorphic slate and quartzite crops 
out. These rocks were considered by Larsen (1948) 
to belong to the Bedford Canyon Formation. Within 
the northeastern part of the Poway quadrangle, a 
similar succession was included by Hanna within 
his "Black Mountain Volcanics." In this study the 
rocks at both of these exposures have been included 
in the Santiago Peak Volcanics. Although they differ 
somewhat from more characteristic Santiago Peak 
Volcanics, the difference is not deemed enough to 
correlate them with the Bedford Canyon Formation. 

Age estimates for the Santiago Peak Volcanics 
have ranged from Late Triassic (Hanna, 1926) to 
mid-Cretaceous (Milow and Ennis, 1961). However 
Fife et al. ( 1 967) showed them to be latest Jurassic 
(Portlandian) based on fossils from sedimentary in- 
terbeds. 



(45) 



46 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 




Figure 1. Index map showing the location of the La Mesa. Poway, and SW 1/4 Escondido 7.5-minute quadrangles. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



47 



COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN 



Qbp I '^''P- ^"^ Point Formation 

OIn, LIndovista Formation 



Tsd, San Diego Formation 

Tp, Pomerado Conglomerate 
Tmv, Mission Valley Formation 
Tst, Stadium Conglomerate 

Tf, Friars Formation 

Tsc, Scripps Formation 
To, Ardatti Stiale 
Tt, Torrey Sandstone 
Td, Delmor Formation 
Tms, Mount Soledad 

Formation 
Kcss, Cobrillo Formation 

(sandstone port) 
Kccg, Cabrillo Formation 
(conglomerate port) 
Kp, Point Loma Formation 
Kl, Lusardi Formation 
Jsp, Santiago Peak Volcan 




Kg, Granitic rocks of ttie 
souttiern California 
batliollth 



Figure 2. Columnar section of the San Diego continental 
margin. 

Plutonic Rocks of the 
Southern California Batholith 

Plutonic rocks of the southern California 
batholith in the area are quartz diorite and gabbro. 
The quartz diorite is typically coarse grained, light 
gray and contains large phenocrysts of plagioclase 
and potassium feldspar. Hornblende and biotite are 
present in small amounts. The gabbro varies con- 
siderably in texture and composition but is mostly 
medium to coarse grained and medium to dark gray. 
The chief minerals are calcic feldspar and pyroxene, 
and the accessory minerals include trace amounts of 
quartz and biotite. 

Potassium-argon dates of a gabbro near San 
Marcos and a quartz diorite 10 km southeast of 
Escondido are respectively 101 and 105 million 
years (Evernden and Kistler, 1970). A lead-alpha 
date on zircon from quartz diorite in the Woodson 
Mountain area, 20 km southeast of Escondido, is 
105 ± 10 million years (Bushee et aL. 1963). 

Throughout most of the area, the granitic rocks 
are deeply weathered. Spheroidal boulders, formed 
as a result of the weathering, range in size from 0.5 
meter to 10 meters. The batholithic rocks where 
weathered are locally very difficult to distinguish 
from the overlying Eocene Friars Formation, which 
is largely composed of debris derived from the 
weathered plutonic basement rock. Careful 
examination for relict primary features in the 
plutonic rocks or sedimentary structures in the 
overlying rocks is necessary to distinguish the 
weathered basement rock from the sedimentary 
strata. 



Rosario Group 

The Rosario Group consists of marine and non- 
marine clastic rocks that, oldest to youngest, in- 
clude the Lusardi Formation, the Point Loma For- 
mation, and the Cabrillo Formation. Only rocks of 
the Lusardi Formation crop out in the La Mesa- 
Poway-Escondido area. 

Lusardi Formation 

The Lusardi Formation, in its type area near 
Rancho Santa Fe, is a very poorly sorted, deeply 
weathered boulder conglomerate (Nordstrom, 
1970). The few exposures of the Lusardi Formation 
that occur in the mapped area are in a narrow belt 
that extends northeastward from the city of Poway 
(plate 2B). These deposits fill a former stream chan- 
nel, but the present topography is reversed, with the 
conglomerate now capping a long narrow ridge. The 
modern drainage is deeply incised into the granitic 
rocks on either side of the ridge. 

The Lusardi Formation at this locality consists 
of poorly sorted, angular to well-rounded clasts that 
range in size from granules to boulders; some of the 
boulders exceed 3 m in diameter. The matrix is a 
medium- to fine-grained quartz and feldspar-rich 
sandstone that comprises about 50 percent of the 
unit. 

The largest and most abundant clasts include 
coarse-grained diorite, quartz diorite, and medium- 
grained granodiorite. These rock types, together 
with minor amounts of aplite and vein quartz, con- 
stitute about 60 percent of the clasts in the Lusardi 
Formation. Other clasts include a variety of fine- to 
very fine-grained, greenish-gray, and dark-gray 
metamorphosed tuff. Some of the most distinctive 
and abundant of these clasts have finely crenulated 
flow banding on weathered surfaces and are very 
fine grained, dark, and structureless on fresh sur- 
faces. Less distinctive but abundant clasts are fine- 
grained black hornfels and volcanic rocks. 

Most of the rock types found in the Lusardi 
Formation-are common to the coarse fraction of the 
Rosario Group as a whole and are considered to be 
derived largely from local plutonic and metamorphic 
rocks (Peterson, 1971). 

The Lusardi Formation rests unconformably on 
granitic rocks of the southern California batholith 
and is in turn overlain by the Eocene Stadium 
Conglomerate. The character and distribution of the 
deposits suggest that the clasts of the Lusardi For- 
mation originated east of the area mapped and 
flowed through a long, narrow, fairly steep-walled 
river channel in the vicinity of Poway. The Lusardi 
Formation lies buried below the San Diego coastal 
area from the vicinity of Carlsbad south to the 
Mexican Border (Kennedy and Moore, 1971). 



EOCENE DEPOSITS 
La Jolla Group 

The La Jolla Group (Eocene) is composed of 
intertongued marine, lagoonal, and nonmarine silt- 



48 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



stone, sandstone, and conglomerate. These rocks, 
though partially age equivalent, are from oldest to 
youngest the Mount Solcdad Formation, Del Mar 
Formation, Torrey Sandstone, Ardaih Shale, Scripps 
Formation, and Friars Formation (Kennedy and 
Moore, 1971). Only the Friars Formation crops out 
in the La Mesa-Poway-Escondido area. 

Friars Formation 

The Friars Formation is a nonmarine and 
lagoonal sandstone named for exposures along the 
north side of Mission Valley near Friars Road in the 
La Jolla quadrangle (Kennedy and Moore, I 971 ). A 
molluscan fauna collected from the type section in- 
cludes Nekewis to (Gabb) and Ectinochilus canalifcr 
supraplicarus (Gabb). These species together are in- 
dicative of the west coast Californian molluscan 
"Transition stage" and a late middle Eocene age 
(Givens, 1974). 

Most of the area is underlain by the nonmarine 
facies, which reaches a maximum thickness of 150 
m and consists of sandstone with interbeds of 
claystone. The sandstone is massive, yellowish gray, 
medium grained, poorly indurated, and caliche-rich. 
The claystone is dark greenish gray, well indurated, 
and expansible. Fluviatile cobble conglomerate len- 
ses and tongues that thicken markedly to the east are 
especially characteristic of the exposures along the 
eastern margin of the area. 

Throughout the mapped area, the Friars For- 
mation rests unconformably on the basement com- 
plex and is overlain by sedimentary deposits of 
Eocene, Pleistocene, and Holocene age. 

Landslides are common in the clay-rich part of 
the formation. The clay is predominantly mont- 
morillonite, but kaolinite is also present. Sixteen 
clay samples were collected and physical charac- 
teristics were analyzed. The results are presented 
on table 1 and are discussed below under Landslide 
Deposits. 



Poway Group 

The Poway Conglomerate of Ellis (1919) is one 
of the most widespread and distinctive rock units in 
southern California. It crops out primarily in the 
eastern part of the San Diego area and is the 
dominant formation in the Poway and La Mesa 
quadrangles (plates 2B,3B). The rock is mostly non- 
marine sandstone and coarse cobble conglomerate 
composed largely of clasts that have been described 
in detail by Bellemin and Merriam (1958), DeLisle 
et al. (1965), Woodford et al. (1968), and Peterson 
(1970a). 

In a recent revision of the Eocene stratigraphic 
nomenclature of the San Diego area (Kennedy and 
Moore, 1971), the Poway Conglomerate was raised 
to the Poway Group and three formations were 
recognized within it: a lower conglomerate 
designated the Stadium Conglomerate, an in- 
termediate sandstone designated the Mission Valley 
Formation, and an unnamed upper conglomerate 
formation. This upper conglomerate unit has been 



subsequently designated the Pomerado 
Conglomerate (Peterson and Kennedy, 1974). 

The arrangement of the three formations in the 
Poway Group is schematically illustrated in figure 3. 
The Mission Valley Formation interlongues with the 
underlying Stadium Conglomerate. Where the 
Mission Valley Formation pinches out and the 
Pomerado Conglomerate overlies the Stadium 
Conglomerate in the eastern part of the area, the two 
units cannot be distinguished. On the geologic map, 
where this situation exists, a dashed contact line in- 
dicates the approximate location of the boundary 
between these formations. 




.? °7i\° °l'° o°o° 



Figure 3. Schematic diagram o( lithostratigraphic variations 
in the Poway Group and modern erosion surface. 

Stadium Conglomerate 

The type section of the Stadium Conglomerate 
lies within the SW 1/4 La Mesa quadrangle and is 
approximately 1 km west of Murphy Canyon Road 
along the northern wall of Mission Valley near San 
Diego Stadium (Kennedy and Moore, 1971). At the 
type section it consists of a cobble conglomerate 
with a dark yellowish-brown coarse-grained sand- 
stone matrix. The massive conglomerate contains 
dispersed lenses of fossiliferous crossbedded sand- 
stone. The fossils include calcareous 
nannoplankton, mollusks. and Foraminifera. The 
nannoplankton include Reticulofenestra umbilica 
(Levin) and Discoaster distinctus Martini. These 
species when considered with the entire flora collec- 
ted indicate a middle or late Eocene age (Kennedy, 
1973). 

The Stadium Conglomerate is moderately well 
sorted with clasts of cobble size predominating. 
Boulders as large as 0.5 m in diameter do occur but 
are extremely rare. Fine-grained rocks within the 
Stadium Conglomerate generally constitute less than 
20 percent of the unit, but locally sandstone beds 
and lenses may comprise as much as 50 percent of 
the unit. 

The highly distinctive "Poway" clasts consist 
predominantly (up to 80 percent) of mildly 
metamorphosed rhyolitic to dacitic volcanic and 
volcaniclastic rocks and up to 10 percent quartzite. 
This suite of clasts first appears in the Eocene for- 
mations of the San Diego area and is typical of 
stratal units such as the Stadium Conglomerate and 
Pomerado Conglomerate. The clasts also are abun- 
dant and characteristic in later stratal units such as 
the Pliocene San Diego Formation, the Pleistocene 
Lindavista Formation, and the various Quaternary 
surficial deposits. 

The volcanic and pyroclastic clasts of the 
Poway suite are distinctively different from the local 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



49 



Santiago Peak Volcanics and no local quartzite out- 
crops, which compare to the quartzite clasts in the 
Eocene conglomerate, are known. The provenance 
of the "Poway" clasts has provoked considerable 
controversy, and widely differing source areas 
ranging from the Mojave Desert to Sonora, Mexico, 
have been proposed (DeLisle et al.. 1965; Merriam, 
1968; Woodford et al.. 1968; Minch, 1972). The 
direction of stratigraphic thinning, cobble im- 
brications, and cross-bedding within the Stadium 
Conglomerate imply that the clasts were transported 
into their present position from an easterly direc- 
tion. 

The Stadium Conglomerate conformably 
overlies the Friars Formation and is conformably 
overlain by the Mission Valley Formation. 

Mission Valley Formation 

The Mission Valley Formation is composed of 
marine, lagoonal, and nonmarine sandstone that lies 
conformably upon the Stadium Conglomerate and is 
conformably overlain by the Pomerado 
Conglomerate. The Mission Valley Formation has a 
maximum thickness of 60 m and was named for ex- 
posures along the south wall of Mission Valley on 
the west side of State Highway 163 in the adjacent 
La Jolla quadrangle (Kennedy and Moore, 1971). 
The sandstone is characteristically soft and friable, 
light olive gray, and fine to medium grained. It is 
locally interstratified with carbonate cemented beds. 
Cobble conglomerate tongues within the Mission 
Valley Formation, which are identical to the 
Stadium Conglomerate in lithology, comprise up to 
30 percent of sections measured in the easternmost 
exposures but less than 15 percent of sections 
measured in the western part of the area. 

Due to the friable nature of the Mission Valley 
Formation, it lacks the bold topographic expression 
of the resistant conglomerate formations that lie 
stratigraphically above and below. Thin deposits of 
conglomeratic slope wash commonly mask the 
Mission Valley Formation in the eastern part of the 
area, where it is overlain by the Pomerado 
Conglomerate. The slopes developed in this area are 
relatively steep on the Pomerado Conglomerate, 
shallow on the Mission Valley Formation, and steep 
on the Stadium Conglomerate. An understanding of 
these topographic relationships helps to determine 
the distribution of the Mission Valley Formation in 
areas where it is covered by surficial deposits. 

The Mission Valley Formation thins from west 
to east (figure 3), pinching out in the eastern part of 
the Poway and La Mesa quadrangles(plates 2B, 3B). 
The rock contains an upper Eocene molluscan 
fauna. An assemblage collected from the uppermost 
beds of the Mission Valley Formation in a road cut 
200 m due east of the Miramar Reservoir filtration 
plant (elevation 238 m) at Lat 32° 54.8' N.; Long 
1 17° 05.7' W. includes Tellina tehachapii Anderson 
and Hanna, MacrocaUista Anderson! Dickerson, 
Crassatella uvasana s.s. Gabb, and Turritella uvasana 
sargeanti (Anderson and Hanna). These species 
when considered together are indicative of the upper 
Eocene age (Tejon Stage) and correlative with the 
upper Eocene of Europe (Givens, 1974). 



Pomerado Conglomerate 

The Pomerado Conglomerate is the uppermost 
formation of the Poway Group and has a maximum 
thickness of 55 meters. It was named for exposures 
located at the divide between Carroll Canyon and 
Poway Valley along Pomerado Road (Peterson and 
Kennedy, 1974). The Pomerado Conglomerate is a 
massive cobble conglomerate, lithologically iden- 
tical to the Stadium Conglomerate. The contact bet- 
ween the Mission Valley Formation and Pomerado 
Conglomerate is conformable and gradational. East 
of the pinch-out of the Mission Valley Formation, 
where the Pomerado Conglomerate rests directly on 
the Stadium Conglomerate, the contact is based on 
an eastern projection of the feather edge of the 
Mission Valley Formation along an assumed 
horizontal surface. 

Both the Stadium Conglomerate and Pomerado 
Conglomerate are characterized by occasional thin 
beds, lenses, and tongues of light brown medium- 
grained sandstone. Most of these are not large 
enough to map. Locally they constitute up to about 
20 percent of the formation. 

A 10 m thick sandstone lens, designated the 
Miramar Sandstone Member of the Pomerado 
Conglomerate (Peterson and Kennedy, 1974), crops 
out in the vicinity of Miramar Reservoir. 
Lithologically, the Miramar Sandstone Member is 
nearly identical to the Mission Valley Formation but 
is stratigraphically higher and wholly contained 
within the Pomerado Conglomerate. Its outcropping 
characteristics and topographic expression are also 
very similar to those of the Mission Valley For- 
mation. 

The Pomerado Conglomerate and associated 
Miramar Sandstone Member have not yielded 
fossils; but, on the basis of its stratigraphic 
relationship with the underlying fossiliferous 
Mission Valley Formation (figure 3) , it is assigned 
to the upper Eocene. 

POST-EOCENE DEPOSITS 
Pliocene and Pleistocene Rocks 

The Pliocene and Pleistocene rocks include 
marine sandstone and conglomerate of the Pliocene 
San Diego Formation, marine and nonmarine sand- 
stone of the late Pliocene or early Pleistocene Lin- 
davista Formation, and lagoonal and nonmarine 
sandstone of the late Pleistocene Bay Point For- 
mation. The Bay Point Formation is not present in 
the La Mesa-Poway-Escondido quadrangles. 

San Diego Formation 

The San Diego Formation (Dall, 1898), middle 
or late Pliocene in age, crops out along the upper 
part of the north facing slopes of Mission Valley. 
These exposures, which attain a maximum thickness 
of 30 m, are typically yellowish-brown, fine- to 
medium-grained, poorly indurated sandstone. Cob- 
ble conglomerate beds, bentonite, marl, and brown 
mudstone further characterize the section. The San 
Diego Formation increases to the south, where it 



50 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



has a maximum thickness of about 400 m (Hertlein 
and Grant, 1939). The lower 200 m of this section 
correlates with the Miocene-Pliocene Rosarito 
Beach Formation in northern Baja California. The 
cobble-conglomerate stringers are composed 
primarily of "Poway-type" clasts ; but, in some beds, 
clasts of granitic and metavolcanic rocks, derived 
from the local basement, comprise up to 50 percent 
of the total. The bentonite is light brown, waxy to 
earthy, expansible, and soft. 

The San Diego Formation rests unconformably 
on rocks of the Poway Group and is overlain by the 
Lindavista Formation, Locally it is separated from 
the Lindavista Formation by an unconformity, but 
elsewhere the bedding of the two units is parallel 
and appears gradational. 

Lindavista Formation 

The Lindavista Formation was named by Hanna 
(1926) for exposures at the Lindavista railroad 
siding 4 km west of the mapped area within the La 
Jolla 7.5 minute quadrangle. The formation consists 
of nearshore marine, beach, and nonmarine 
sediments deposited on a 10 km wide wave-cut plat- 
form (Lindavista Terrace of Hanna, 1926) during a 
period of time that post-dates the San Diego For- 
mation of middle or late Pliocene age and pre-dates 
the fossiliferous late Pleistocene (Sangamon Stage) 
Bay Point Formation. A fossil molluscan fauna 
found in the Lindavista Formation near Lat. 32° 
48.5' N.; Long. 1 17° 6.25' W., includes the extinct 
species Pecten bellus. Because this species is not 
known from the late Pleistocene, the Lindavista For- 
mation at this locality is considered to be early 
Pleistocene in age (G. Kennedy, 1973). 

The Lindavista Formation in the mapped area is 
reddish-brown sandstone and conglomerate. 
Ferruginous cement, mainly hematite, gives the Lin- 
davista Formation its characteristic color and a 
resistant, ledgy nature. 

Both the coarse and fine-grained rocks of the 
Lindavista Formation have been largely derived 
from Eocene formations of the area, particularly the 
Poway Group. Iron-staining is common to the Lin- 
davista Formation, and, where it extends downward 
into the underlying Eocene rocks, the two become 
difficult to differentiate. A particularly difficult area 
for separating the Lindavista Formation from ex- 
tensively stained Stadium Conglomerate lies east 
and southeast of Miramar Naval Air Station in the 
vicinity of Camp Elliott. The upper surface of the 
Lindavista Formation is commonly characterized by 
"mima mounds" or "Prairie Mounds," small mound- 
like hills up to about 10 m in diameter and 1 m high 
which are useful in differentiating this unit from the 
rocks of the Poway Group. 



Pleistocene and Holocene 
Surficial Deposits 

The Pleistocene and Holocene surficial 
deposits include stream-terrace, landslide, 
alluvium, and slope wash deposits. 



St re a nn -Terrace Deposits 

Stream-terrace deposits have been preserved in 
only a few places in the mapped area. These include 
a poorly consolidated, conglomeratic sand deposit 
near the confluence of Sycamore Canyon and the San 
Diego River channel, approximately 2 km west of 
Santee, and a coarse-grained sand deposit at the 
mouth of Mission Gorge near Mission Valley. Also 
unmapped conglomeratic stream-terrace deposits 
are found in several road cuts excavated for the old 
Mission Gorge highway, approximately 0.5 km nor- 
theast of the gaging station shown on plate 3B. 

Landslide Deposits 

The area is underlain in large part by in- 
competent sedimentary rocks which have been 
broadly dissected by shallow weslward-tTowing 
streams. Most of the landslides in the map area are 
rotational slumps and have occurred along valley 
walls where rocks of the Friars and Mission Valley 
Formations occur. The sliding, commonly 
associated with soft, expansible clay beds within 
these units, is the result of the combined factors of 
incompetent rock, ground water, steep slope angle, 
and basal undercutting of slopes by streams. 

Most of the stream channels that dissect the 
soft sedimentary cover are strongly asymmetrical 
with their steep side exposed to the north. These 
slopes are commonly I to 15 degrees steeper than 
those facing south which seldom reach angles 
greater than 30 degrees. The over-steepening is con- 
trolled in part by the presence of resistant im- 
permeable rock layers (Pomerado and Stadium 
Conglomerate) exposed along the upper slopes as 
erosional ledges and platforms. The ledges protect 
the softer incompetent material directly beneath 
them (Friars and Mission Valley Formations) from 
erosion. Westward-thinning conglomerate tongues 
of the Pomerado and Stadium Conglomerates crop 
out along the upper valley slopes over a large part of 
the area that lies between Rancho Bernardo and 
Fortuna Mountain(plates 2B, 3B). Landslides occur 
beneath these beds in the soft sandstone and 
claystone of the Friars and Mission Valley For- 
mations. 

Several man-induced slides in the Rancho Ber- 
nardo area were studied, and all were found to occur 
beneath resistant conglomerate layers within the 
soft sandstone and claystone. Stability filling (com- 
pacted fill placed over a benched cut slope) may be 
one means by which this type of failure can be 
avoided. Because landslide incidence is greatly in- 
creased during periods of high rainfall, as a result of 
lowered internal rock strength, subdrainage may be 
another means of slope control. 

Slopes steeper than 30 degrees underlain by 
clay-rich facies of the Friars Formation in the Ran- 
cho Bernardo, Poway Valley, and Mission Gorge 
areas are mantled with surficial landslide debris 
that coalesces with slope wash and alluvium in the 
valley bottoms. Sixteen samples of claystone were 
collected from these areas (plates 1 B-3B) and analyz- 
ed for their physical properties. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



51 



The results of Atterberg tests and the quantity 
of individual size fractions from particle size 
distribution tests of these samples are shown in 
table 1. 

For engineering purposes the clay fraction is 
defined as less than 0.002 millimeter (mm), the silt 
fraction from 0.002 to 0.074 mm, and sand from 
0.074 to 2.0 millimeters. The liquid limit (LL) is 
defined as the minimum moisture content at which 
the material behaves as liquid using this test. The 
plastic limit (LP) is defined as the minimum 
moisture content at which the sample behaves 
plastically using this specified test procedure. The 
plasticity index (IP) is the numerical difference bet- 
ween the liquid limit and the plastic limit. The 
plasticity index is then the range of moisture content 
over which the sample behaves plastically. There 
exists a direct relationship between the liquid limit 
and "compression index," and between the liquid 
limit and the "coefficient of consolidation," whereas 
an inverse relationship exists between the plasticity 
index and "shearing resistance" (lerzaghi and Peck, 
1967). 

The stated median particle size was taken from 
the 50 percent cumulative level of particle size 
distribution graphs. The arithmetic mean of the 
median particle sizes among all the samples is 0.016 
mm (16 microns), which is in the lower portion of 
the silt range. 

Associations between plasticity index, particle 
size, and the percentage of clay-size particles are 
readily observed from the data of table 1. The 
medium-plasticity samples (IP=il0 to 20) have an 
average median particle size of 47 microns. High- 
plasticity samples (IP = 20 to 40) have an average 
median particle size of 14 microns. The very-high- 
plasticity samples (IP > 40) have a mean particle 
size of 6 microns. A direct relationship between 
higher plasticity and landslide incidence can be seen 
by comparing this data with field observations in 
that both the surficial and bedrock landslides in the 
areas sampled are more abundant with an increase 
in the plasticity index. Nearly all of the landslides 
mapped have occurred in rocks with a plasticity in- 
dex greater than 20. 

Alluvium and Slope Wash 

Alluvium in the area consists primarily of 
poorly consolidated stream deposits of silt, sand, 
and cobble-sized particles derived from bedrock 
sources that lie within and to the east of the study 
area. The alluvium is intertongued with Holocene 
slope wash that generally mantles the lower valley 
slopes throughout the area. For this reason, 
alluvium and slope wash have not been dif- 
ferentiated in most areas. 

The slope wash deposits consist primarily of 
poorly consolidated surficial materials derived from 
nearby soil and decomposed bedrock sources. This 
reworked debris is deposited along the flanks of the 
lower valley slopes by the action of gravity and sur- 
face water. Thick deposits of slope wash are com- 
monly associated with thick soil horizons developed 
on the Friars and Mission Valley Formations. Ex- 



pansive clay horizons weathered from bedrock sour- 
ces and deposited as slope wash yield the hum- 
mocky topography that is common to much of this 
area. 



STRUCTURE 
AND SEISMIC HISTORY 

The oldest rocks in the study area, the upper 
Jurassic Santiago Peak Volcanics are massive, com- 
plexly deformed, and their structure within the mapped 
area is not readily decipherable. They have undergone 
low-grade metamorphism and have been intruded by 
rocks of the mid-Cretaceous southern California 
batholith. 

Regional uplift followed deformation, 
metamorphism, and batholithic intrusion near the close 
of the Mesozoic Era, and deep-seated batholithic rocks 
were extensively exposed. An erosion surface having in 
excess of 500 m relief was developed on these rocks, 
setting the stage for deposition of sedimentary rocks in 
the Late Cretaceous and Tertiary periods (Peterson 
and Nordstrom, 1970). 

The basement rocks have acted as a rigid platform 
from Late Cretaceous time to the present and the post- 
batholithic sedimentary rocks deposited upon them are 
only slightly deformed and mostly flat-laying (section 
A-A', B-B'). Mapping of the rock units over a broad 
area has demonstrated that inclinations locally associ- 
ated with Tertiary and Quaternary faulting are rarely 
greater than 2 degrees. 

Evidence for Late Cenozoic uplift and faulting 
within the mapped area is abundant (Moore and Ken- 
nedy, 1970; Peterson, 1970b; Moore, 1972; Ziony and 
Buchanan, 1972). Uplift of the Lindavista terrace is 
evident in that the early Pleistocene shoreline associ- 
ated with the present landward extension of the Lin- 
davista Formation lies at an altitude of nearly 1 65 m in 
the western part of the Poway and La Mesa quad- 
rangles. 

The Poway terrace, which is extensively developed 
in the eastern part of the Poway and La Mesa quad- 
rangles, lies at an altitude of about 275 to 325 meters. 
Hanna ( 1 926) and others consider the Poway terrace to 
be the result of Pleistocene marine planation like that 
of the Lindavista terrace. Possibly this planar surface is 
a stripped structural surface developed on the resistant 
upper surface of the Pomerado Conglomerate. 

Pleistocene or younger faults in the study area oc- 
cur in the vicinity of Collwood Boulevard and Mon- 
tezuma Road, Murphy Canyon, and Mission Gorge. A 
post-Lindavista fault is inferred to coincide with at 
least the southern part of Murphy Canyon and the 
southern part of Mission Gorge because the Lindavista 
Formation lies topographically higher on the west side 
of these canyons. 

Holocene seismic activity along several faults that 
lie within 10 km of the area is supported by (1) the 
historic seismicity believed to be associated with the 
Rose Canyon fault zone in the San Diego Bay area and 
(2) subbottom acoustic profiles showing Holocene sedi- 
ments offset on the sea floor at a location 25 km north 
of La Jolla within the Rose Canyon fault zone (Moore, 
1972). 



52 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 





Table 


?. Atterberg limits and 


particle 


size distribufion. 






Location 
{All San Bernardino 
Base and Meridian) 


Atterberg Limits 


Particle Size 




No. on 
map 


Liquid 
limit 


Plastic 
limit 


Plastic- 
ity index 


Sand 
(%) 


Silt 
(%) 


Clay 


Mineralogy* 


1 


Sec. 31, T. 13 S., R. 2 W., 13S0 m 
south of intersection of Black 
Mountain Road and Rancho 
Bernardo Road in small road cut 
on east side. 


55 


30 


25 


19 


69 


12 


Mostly montmorillonite, some mica, 
trace of kaolinite. 


2 


Sec. 22, T. 13 S., R. 2 W., road cut on 
southwest corner of intersection of 
Rancho Bernardo and West Ber- 
nardo Drive, 3 m above road level. 


52 


22 


30 


13 


83 


4 


Mostly montmorillonite, some mica, 
trace of kaolinite, and minor 
quartz. 


3 


Sec. 27, T. 13 S., R. 2 VV., Rancho 
Bernardo Industrial Center de- 
velopment. Cut beneath southeast 
corner of National Cash Register 
Co. building, 3 m below contact 
between the Stadium Conglomer- 
ate and P'riars Formation. 


79 


30 


49 


8 


60 


32 


Mostly montmorillonite, trace of 
kaolinite. 


4 


Sec. 27, T. 13 S., R. 2 \V., 40 m west 
of intersection of Center Drive and 
U.S. Highway 395 near Rancho 
Bernardo in small cut on south 
side at base of exposure. 


58 


27 


31 


3 


61 


36 


Mostly montmorillonite, trace of 
quartz. 


S 


Sec. 27, T. 13 S., R. 2 W., 275 m 
south of Lomica Drive in Rancho 
Bernardo on Center Drive in high 
road cut on east side at elevation 
180 m (approximately 1.5 m above 
street level). 


53 


22 


31 


8 


61 


31 


Mostly montmorillonite, trace of 
kaolinite and quartz. 


6 


10 m vertically above number 5. 


44 


19 


25 


21 


55 


24 


Mostly montmorillonite, trace of 
quartz. 


7 


22 m vertically above number 5. 


74 


29 


45 





60 


40 


Mostly montmorillonite, trace of 
quartz. 


8 


Sec. 17, T. 14 S., R. 2 W., 850 m 
north of Poway Road on east side 
of U.S. Highway 395 in road cut. 
Sample collected 3 m above road 
level at contact between green 
claystone of the Friars Formation 
and rocks of the Santiago Peak 
Volcanics. 


63 


25 


38 


14 


69 


17 


Mostly montmorillonite, minor 
quartz. 


9 


3 m vertically above number 8 at 
contact between Stadium Con- 
glomerate and Friars Formation. 


60 


20 


40 


4 


62 


34 


Mostly montmorillonite, minor 
quartz. 


10 


Sec. 14, T. 14 S., R. 2 W., 1125 m 
east of Pomerado Road on north 
side of Poway Road in road cut at 
base. 


47 


25 


22 


27 


56 


17 


Mostly montmorillonite, minor 
quartz, trace feldspar. 


11 


Sec. 26, T. 14 S., R. 2 W., 600 m 
south of intersection of Pomerado 
Road near Becler Canyon Road on 
Pomerado Road; 2 m beneath 
Stadium Conglomerate on west 
side of road. 


57 


21 


36 


4 


82 


14 


Mostly montmorillonite, trace of 
mica, trace of kaolinite, minor 
quartz and feldspar, trace of cal- 
cite. 


12 


Sec. 35, T. 15 S., R. 2 W., intersec- 
tion of Old Mission Gorge Road 
and New Mission Gorge Road at 
southeast corner 900 m east of 
number 13 and 1 m above road 
level. 


60 


10 


50 


15 


55 


30 


Mostly montmorillonite, trace of 
mica, minor kaolinite, trace of 
quartz and feldspar. 



:ontinued on page following. 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



53 





Table 


I. Atferberg limits and particle size disfribution 


continued). 




Location 
{All San Bernardino 
Base and Meridian) 


Atterberg Limits 


Particle Size 




No, on 
map 


Liquid 
limit 


Plastic 
limit 


Plastic- 
ity index 


Sand 
(%) 


Silt 
(%) 


Clay 

(%) 


Mineralogy* 


13 


Sec. 2, T. 16 S., R. 2 W., southeast 
side of Mission Gorge Road 900 m 
south of intersection of Old Mis- 
sion Gorge Road and 1140 m 
northeast of Conestoga Way. 
Locality is 1 m above road level. 


66 


IS 


41 


24 


47 


29 


Mostly montmorillonite, minor kao- 
linite, trace of quartz and feldspar. 


14 


Sec. 18, T. 18 S., R. 3 W., 400 m west 
of Murphy Canyon Road on Friars 
Road in high cut on north wall of 
Mission Valley, 3 m above base of 
cut and S m beneath Stadium Con- 
glomerate. 


52 


21 


31 


12 


63 


25 


Mostly montmorillonite, trace of 
mica, minor kaolinite, trace of 
quartz and feldspar. 


15 


Sec. 16, T. 18 S., R 3 W., 365 m 
northeast of intersection between 
Interstate Highway 8 and Waring 
Road; 2 m above base of cut on 
Frontage Road, 244 m east of 
Waring Road. 


59 


24 


35 


38 


46 


16 


Mostly montmorillonite, trace of 
mica, minor kaolinite, trace of 
quartz, feldspar and calcite. 


16 


Sec. 15, T. 18 S., R. 3 W., 550 m due 
west of the intersection between 
Interstate Highway 8 and College 
Avenue on south side of Mission 
Valley in road cut at San Diego 
State College, 3 m above road 
level. 


52 


20 


32 


5 


74 


21 


Mostly montmorillonite, minor mica 
and quartz, trace of feldspar and 
calcite. 



* Analyses made by Paul Anderson, California Division of Mines and Geology Laboratory. 



Forty-four earthquakes with magnitudes bet- 
ween 2.5 and 3.7 have been recorded within the 
greater San Diego metropolitan area since 1950. 
Three of these which occurred in 1964 on June 21, 
June 22, and July 14 had epicenters within the 
vicinity of San Diego Bay and magnitudes of 3.7, 
3.6, and 3.5 respectively. 

The San Diego area has experienced ground 
shaking produced by earthquakes with epicenters as 
distant as 100 kilometers. The 1933 Long Beach 
earthquake (M 6.6) caused minor damage in San 
Diego County and was felt sharply as far south as 
the Mexican border. 

On November 4, 1949, and February 9, 1956, 
earthquakes on the Vallecitos -San Miguel fault in 
northern Baja California were felt in San Diego. The 
1949 earthquake (M 5.7) had an epicentral distance 
of approximately 75 km southeast of San Diego. The 
epicenter of the 1956 earthquake (M 6.8) was ap- 
proximately 1 75 km south of San Diego and caused 
ground rupture for 20 km in the vicinity of the 
epicenter (Shor and Roberts, 1958). Three af- 
tershocks of this earthquake with magnitudes 
greater than 6 occurred on February 9, 14, and 15, 
1956. Several earthquakes (M > 5) on the Agua 
Blanca fault, also in northern Baja California, have 
been recorded during the past 30 years with epicen- 
tral distances within 1 25 km of the San Diego civic 
center. 

During the past 35 years at least ten of the 
strongest earthquakes that have occurred in the Im- 



perial Valley-Salton Trough have been felt in San 
Diego. Three of these, the 1940 Imperial Valley ear- 
thquake (M 7.1), the 1951 Superstition Hills earth- 
quake (M 5.6), and the 1968 Borrego Mountain 
earthquake (M 6.5) caused minor damage in western 
San Diego County. 

The February 9, 1971, San Fernando Valley 
earthquake (M 6.4) was felt sharply in San Diego. 
Minor damage occurred in the coastal area as far 
south as National City. Several small rockfalls oc- 
curred in roadcuts on Highway 395 between Poway 
and Miramar Roads. 



MINERAL RESOURCES 



Mineral resources in the Escondido, Poway, 
and La Mesa quadrangles(plates 1B-3B) include ex- 
tensive deposits of sand, gravel, and metavolcanic 
rock suitable for use as aggregate in highway 
asphalt, Portland cement, and ceramic products. 
Large reserves of decomposed granite, small ton- 
nages of pyrophyllite, and minor amounts of ar- 
senopyrile, gold, silver, and uranium are also 
present. 

Clay in the Friars Formation has not been com- 
mercially mined within the mapped area but 
represents a potential source of expansible clay, fire 



54 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 



BULL. 200 



clay, and lightweight aggregate. Table 1 summarizes 
the physical properties of 16 clay samples collected 
from the Friars Formation. 

The mineral resources and mineral industry of 
San Diego County are discussed in detail by Weber 



(1963). The mines, pits, and quarries in the area are 
listed in table 2. Mineral-resource inventories are 
made annually by the Natural Resources Division, 
San Diego County Department of Agriculture, and 
are available to the public through the agency. 



Table 2. Mines, quarries, and pifs in the La Mesa, Poway, and SE'A Escondido quadrangles. 



Mines, quarries, or pits* 


Location 
{All San Bernardino 
Base and Meridian) 


Geologic unit 


Mineral resource 


Remarks 


1. BIy Stone Co. Quarry. 


Sec. 10, T. 13 S., R 2 W. 


Plutonic rock of the 
southern California 
batholith. 


Dimension stone. 


Operated from 1921 to 
1924 for large unfrac- 
tured blocks of San 
Marcos Gabbro. 


2. Van Deventer quarry 
(Daley Corporation). 


Sec. 10(.?) T. 13 S., R- 
2 W. 


Plutonic rock of the 
southern California 
batholith. 


Dimension stone. 


Reported byTucker 
(1925) to be on the 
south shore of Lake 
Hodges but exact loca- 
tion is undetermined. 


3. Four-Gee deposit (Golem). 


Sec. 19, T. 13 S., R2 W. 


Santiago Peak Volcanics. 


Pyrophyllite. 


Discovered in 1952 and 
mined since 1953. 


4. Property now owned by 
Rancho Bernardo Inc. 


Sec. 27, T. 13 S., R 2 W. 


Plutonic rock of the 
southern California 
batholith. 


Decomposed granite. 


Inactive 1972; used for 
roadbed fill during ex- 
pansion of U.S. High- 
way 395. 


5. Black Mountain deposit; 
Oliver Wylie estate. 


Sec. 5, T. 14 S., R 2 W. 


Santiago Peak Volcanics. 


Arsenopyrite (Arsenic) 
minor amount of gold 
and silver. 


Operated in 1924 for arse- 
nic and gold. Total re- 
covery reported was 
700 pounds of material 
containing 31.4 per- 
cent arsenic plus a 
small amount of gold 
and silver. 


6. C. B. Grove (Pit No. 2). 


Sec. 10, T. 14 S., R 2 W. 


Plutonic rock of the 
southern California 
batholith. 


Decomposed granite. 


Inactive 1972; active in 
1957. 


7. Fletcher Quarries. 


Sec. 15, T. 14 S., R 2 W. 


Plutonic rock of the 
southern California 
batholith. 


Decomposed granite. 


Inactive 1972. 


8. Einer Brothers (Poway 
Pit). 


Sec. 14, T. 14 S., R 2 W. 


Plutonic rock of the 
southern California 
batholith. 


Decomposed granite. 


Inactive 1972. 


9. Candel and Johnson 
(Poway Operation). 


Sec. 21 & 22, T. 14 S., 
R2W. 


Stadium Conglomerate. 


Concrete sand and 
crushed gravel. 


Inactive 1972; active 
1958. 


10. Escondido Sand and 
Gravel Works. 


Sec. 26, T. 14 S., R 2 W. 


Alluvium derived 
mostly from rocks of 
the Poway Group. 


Concrete and bituminous 
aggregate. 


Inactive 1958. 


11. San Diego Consolidated 
Co., (Carrol Canyon 
Plant). 


Sec. 6, T. IS S., R 2 W. 


Stadium Conglomerate 
and Alluvium. 


Bituminous aggregate. 


Active 1972. 


12. Nelson and Sloan 
(Miramar Plant). 


Sec. 19, T. 15 S., R 2 W. 


Stadium Conglomerate 
and Alluvium. 


Concrete sand and 
crushed gravel. 


Began operation 1956, 
active 1972. 


13. Fenton, H. G., Material 
Co. 


Sec. 20, T. 15 S., R 1 W. 


Alluvium. 


Concrete and plaster 
sand, and crushed 
gravel. 


Inactive 1972. 


14. Fenton, H. G., Material 
Co. 


Sec. 25, T. IS S., R 2 \V. 
& Sec. 30, T. 15 S., R 
1 W. 


Alluvium. 


Concrete and plaster 
sand, and crushed 
gravel. 


Operation began in 1954 
in 200 acres; inactive 
1972. 


IS. Acme Truck Co. (Pit #1) 


Sec. 35, T. 15 S., R 2 W. 


Plutonic rocks of the 
southern California 
batholith. 


Decomposed granite. 


Inactive 1972. 



continued on page follov 



1975 



GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 



55 



Table 2. Mines, 


quarries, and pits in the 


La Mesa, Poway, and SE'/J Escondido quadrangi 


es (continued). 


Mints, quarries, or pits* 


Location 
(All San Bernardino 
Base and Meridian) 


Geologic unit 


Mineral resource 


Remarks 


16. Fletcher Quarries— Ed 
Fletcher Co. 


Sec. 35, T. 15 S., R 2 W. 


Santiago Peak Volcanics. 


Riprap. 


Used in construction of 
Mission Bay Park and 
jetty. 


17. Industrial Asphalt (Plant 
36). 


Sec. 35, T. 15 S., R 2 W. 


Santiago Peak Volcanics. 


Bituminous aggregate. 


Active 1972. 


18. Dennis, V. R., Canyon 
Rock Co. 


Sec. 3, T. 16 S., R 2 W. 


Santiago Peak Volcanics. 


Riprap, concrete aggre- 
gate, bituminous aggre- 
gate. 


Began operations 1929. 


19. Dennis, V. R., Canyon 
Rock Co. 


Sec. 3, T. 16 S., R 2 W. 


Alluvium. 


Ceramic and concrete 
sand. 


San Diego River bed 
sand operation. 


20. Daley Corp. 


Sees. 5 & 8, T. 16 S., R 
2 W. 


Friars Formation and 
Stadium Conglomerate. 


Crushed gravel, for con- 
crete and bituminous 
aggregate. 


Active 1972. 


21. Denton, American Sand 


Sec. 8, T. 16 S., R 2 W. 


Alluvium. 


Plaster sand. 


San Diego River bed; be- 


Inc. 








gan operations in 1951, 
active 1972. 


22. Nelson and Sloan, Mission 
Sand Co. 


Sec. 17, T. 16 S., R 2 W. 


Alluvium. 


Plaster sand. 


San Diego River bed; in- 
active 1972. 


23. Fenton, H. G., Material 
Co. (Mission Valley Plant). 


Sec. 18, T. 16 S., R 2 W. 


Poway Group and Al- 
luvium. 


Concrete sand and 
crushed gravel. 


Active 1972. 


24. Olswick Prospect. 


Sec. 32, T. 15 S., R 1 W. 


Stadium Conglomerate. 


Unidentified uranium 
minerals. 


Mineralized zone in 3m 
wide bulldozer pit 
in sandstone bed 
nearcontactwith 
underlying granitic 
basement rock. An un- 
published short report 
on the site was com- 
pleted by the Atomic 
Energy Commission in 
1955. 


25. Independent Stone Co. 


Sec. 30, T. 16 S., R 1 W. 


Santiago Peak Volcanics. 


Crushed stone. 


Inactive 1972. 



' Compiled in part from Weber, 1963. 



S6 



CALIFO!.. 



THIS BOOK IS DUE ON THE LAST DATE 
STAMPED ■ P'V 

. . >Li -J." ' ' >GY 



BULL. 200 



REFERENCES CITED 



Bellemin. G.J.. and Merriam, R., 1958. Petrology and origin of 
the Poway conglomerate, San Diego County. California; 
Geol. Soc. America Bull., v. 69. p. 199-220. 

Bukry, David, and Kennedy, MP., 1969. Cretaceous and Eocene 
coccoliths at San Diego. California, in Stiort contributions to 
California geology: California Division of f^ines and Geology 
Special Report lOO. p. 33-43. 

Bushee. J., Holden, J., Geyer, B., and Gastil, G., 1963. Lead- 
alpfia dates for some basement rocks of southwestern 
California Geol. Soc. America Bull., v. 74, p. 803-806. 

Dall, W.H., 1898, 18th Ann. Rept.; U.S. Geol. Survey, pt. 2, 
correlation table opp. p. 334. 

DeLisle, M.. Morgan, J.R., Heldenbrand. J., and Gastil. G., 1965, 
Lead-alpha ages and possible sources of metavolcanic 
rock clasts in the Poway conglomerate, southwest Califor- 
nia: Geol. Soc. America Bull., v. 76, p. 1069-1074. 

Ellis, A.J., 1919, Geology, western part of San Diego county, 
California: U.S. Geol. Survey Water-Supply Paper 446. p. 50- 
76. 



Kem, J. P.. 1971, Paleoenvironmental analysis of a late 
Pleistocene estuary in southern California: Journal of 
Paleo., V. 45, p. 810-823. 

Larsen, E.S., 1948, Bathollth and associated rocks of Corona, 
Elsinore. and San Luis Rey quadrangles, southern Califor- 
nia: Geol. Soc. America Mem. 29. 182 p 

Merriam, R., 1968, Geologic reconnaissance of northwest 
Sonora: Stanford University Pubs. Geol. Sci., v. 11, p. 287. 

Milow, E.D., and Ennis, D.B.. 1961. Guide to geologic field trip of 
southwestern San Diego County: Geol. Soc. America Cor- 
dilleran Sec. 57th Ann. Mtg., Guideljook, p. 23-43. 

Minoh, J. A., 1972, The late Mesozoic — early Tertiary framework 
cf continental sedimentation, northem peninsular ranges, 
Baja California, Mexico: Unpublished Ph.D. Dissertation, 
University of California, Riverside. 

Moore, G.W., 1972, Offshore extension of the Rose Canyon 
fault, San Diego, California: U.S. Geol. Survey Prof. Paper 
800-C. 



Evernden, J.F., and Kistler, R.W., 1970, Chronology of em- 
placement of Mesozoic batholithic complexes in California 
and western Nevada: U.S. Geol. Survey Prof. Paper 623, 42 
P 

Fife, D.L., Minch, J. A., and Crampton, P.J., 1967, Late Jurassic 
Age of the Santiago PeaV Volcanics. California: Geol. Soc. 
America Bull., v. 78, p. 299-304. 

Givens. C.R., 1974, Eocene molluscan biostratigraphy of the 
Pine Mountain area, Ventura County, California: University 
of California, Dept. of Geol. Sci. Bull., v. 109, 107 p. 

Gray, C.H., Jr.. Kennedy, MP., and Morton. P.K.. 1971. Petroleum 
potential of southern coastal and mountain area. Califor- 
nia: American Assoc. Petroleum Geologists, Mem. 15. p. 
372-383. 

Hanna, M.A., 1926, Geology of the La Jolla quadrangle. Califor- 
nia: University of California. Dept. Geol. Sci. Bull., v. 16, p. 
187-246. 

Henlein, L.G., and Grant. U.S., IV., 1939, Geology and oil 
possibilities of southwestern San Diego County: California 
Journal Mines and Geol., v. 35. p. 57-78, 

Heniein, L.G.. and Grant, U.S., IV, 1944, The geology and 
paleontology of the marine Pliocene of San Diego. Califor- 
nia, pt. 1. Geology: San Diego Soc. Nat. History Mem., v. 2, 
p. 1-72. 

Kennedy, G L.. 1973. Early Pleistocene invertebrate faunule 
from the Lindavista Formation, San Diego. California: San 
Diego Soc. of Nat History. Transactions, v. 17, p. 119-128. 

Kennedy, MP.. 1973. Stratigraphy of the San Diego embayment. 
California: Unpublished Ph D. dissertation. University of 
California, Riverside. 

Kennedy, M.P., 1975, Geology of the Del Mar. La Jolla and Point 
Loma quadrangles. San Diego metropolitan area, San 
Diego County, California: California Div. Mines and 
Geology Bull. 200A. 

Kennedy, M.P., and Moore. G W.. 1971. Stratigraphic relations of 
upper Cretaceous and Eocene Formations. San Diego 
coastal area, California: American Assoc. Petroleum 
Geologists Bull., v. 55, p. 709-722. 



Moore, G.W., and Kennedy, M.P., 1970, Coastal geology of the 
California-Baja California border area: American Assoc. 
Petroleum Geologists Guidebook, Pacific Section tall field 
trip, p. 4-9. 

Nordstrom, C.E., 1970. Lusardi Formation — a post-toatholithic 
Cretaceous conglomerate north of San Diego. California: 
Geol. Soc. America Bull., v. 81. p. 601-605 

Peterson, G.L.. 1970a, Distinctions between Cretaceous and 
Eocene conglomerates in the San Diego area, south- 
western California: American Assoc. Petroleum Geologists 
Guidebook. Pacific Section fall field trip. p. 90-98. 

Peterson. G.L., 1970b. Quaternary deformation of the San Diego 
area, southwestern California: American Assoc. Petroleum 
Geologists Guidetx)ok, Pacific Section fall field trip. p. 120- 
126. 

Peterson. G.L, 1971. Stratigraphy of the Poway area, south- 
western Califorpip- San Diego Soc. Nat. History Tran- 
sactions, V. 16, no. 

Peterson, G.L., and Kennedy. MP.. 1974, Lithostratigraphic 
variations in the Poway Group near San Diego, California: 
San Diego Soc. of Nat. History Transactions, v. 17, p. 251- 
258. 

Shor, G.G., Jr., and Roberts, E., 1958. San Miguel, Baja Califor- 
nia Norte, earthquakes of February, 1956; a field report; 
Seismological Society of America Bull., v. 48, p. 101-116. 

Terzaghi, K., and Peck, R.B., 1967, Soil mechanics In 
engineering practice: John Wiley and Son, New York, 729 p. 

Weber, F.H . Jr , 1963, Geology and mineral resources of San 
Diego County. California: California Div. Mines and 
Geology County Rept. 3, 309 p. 

Woodford. A.O., Welday. E.E.. and Merriam, R.. 1968. Siliceous 
tuff clasts in the upper Paleocene of southern California; 
Geol. Soc. America Bull . v. 79, p. 1461-1486. 

Ziony. J. I., and Buchanan. J.M.. 1972, Preliminary report on 
recency of faulting in the greater San Diego area, Califor- 
nia; U.S. Geol. Survey Open-File Rept., 16 p. 



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3 1175 00495 9238 



— fj. 



'-?- i-ltCtS 



STATE OF CALIFORNIA 

THE RESOURCES AGENCY 

DEPARTMENT OF CONSERVATION 



PREPARED IN 
THE CITY 




PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 



2H 
C3 




GEOLOGY OF THE DEL MAR QUADRANGLE 
SAN DIEGO COUNTY, CALIFORNIA 

by Michael P. Kennedy 

SCALE 1 24000 



CONTOUR INTERVAL 20 FEET 
DOTTED LINES REPRESENT lOFOOT CONTOURS 
DATUM IS MEAN SEA LEVEL 
DEPTH CURVES AND SOUNDINGS IN FEET— DATUM IS MEAN LOWE 



EXPLANATION 

[q7] 

ArtiBcial fill 



8 >o 

i ^ c 

g en ^ 



Landslide deposits 



Stream-terrace deposita 



Bay Point Formation 




I 



Poway and La Jolla Groups 
TmB. Mitaion VaUey Fomaiion: Tat. Stadium C«n- 
glomeratt: Tf, Friars Formalion; Tacu. Scrippa Par- 
ninftoR (upper (oniTue); Tac, Scrippa FomuUton; Ta. 
Ardath Shale: Tf. Torrey Sanihtonc: Td. Delmar 
Fornuitum: Td A Tf, Delmar and Friara Formation 
uiuliffeTerUiaitd. Conglomerate marked by circle pat- 
tern, aandatone marker bed ahown by dot patttm. 



Lusardi Formation 



EH 



Santiago Peak Volcanics 




:ontrol by USGS and USC & GS 



2.000' - 

i.ooo* - 


^ 


oeifle OcMfi 






CARMEL VALLEY FAULT 




Tsc 


Tt 




Tsc 


Tsc 


SA 






Td 


/ 


Td 


r\ 








Td 






, 


1,000'- 




" ■// 111 


Upp.r Cr.loc.0 


.„..„„ 


,o..U„ 


„.,.„ 


... 


1 


1 




TORREY PINES FAULT 
SALK FAULT 




SYMBOLS 
Contact 

{dashed where approximatety located: 
dotted where cQnce<Ued) 

Fault, showing dip 

{dathed whtre appToximatelu located; 

dotted where ameeaird: V. upthrown 

aide; D. dotDnihrown tide; jr-jr^^ ihear toru). 

Anticline, showing 
direction of plunge. 

H 

Syncline, showing 
direction of plunge. 

X- 

Strike and dip of bedding. 

a 

Landslide with direction of movement 
indicated by arrows. 

Clay sample locality. 

Fossil mollusk locality. 

Fossil coccolith locality. 

Fossil vertebrate locality. 




LOCATION MAP 



11 If 11 



CALIFORNIA DIVISION OF MINES AND GEOLOGY 
JAMES E SLOSSON. STATE GEOLOGIST 



STATE OF CALIFORNIA 

THE RESOURCES AGENCY 

DEPARTMENT OF CONSERVATION 



PREPARED IN COOPE 
WITH 
THE CITY OF SAN [ 




PREPARED m COOPERATION 

WITH 

THE CITY OF SAN DIEGO 



SAN D EGO METROPOLITAN AREA 
BULLETIN 200 PLATE 3A 

30 




GEOLOGY OF THE POINT LOMA QUADRANGLE 
SAN DIEGO COUNTY, CALIFORNIA 

by Miohapl P. Kennedy 

SCALE 1 24000 



DATUM IS MEAN SEA LEVEL 
DEPTH CURVES AND SOUNDINGS IN FEET— DATUM IS I 

1975 
EXPLANATION 



Beach aand 



I LOWER LOW WATER 






Alluvium 

Landslide deposits 

I Qbp I 

Bay Point Formation 



Lin da vista Formation 



Mount Soledad Formati< 



Mission Valley Formation 



Rosario Group 

•formalion {aandilone pari): Kec. Ca ■ 
I (conclomerate pari); Kj>. PoitU Loma 



Contact 

(dtuhed where approrimalcly loco 



Fault, showing dip 

(dathed wherf appranmateiy located; 

dolled where concealed; U. uplhrown 

\' D. douftUhrown nde; -jTinjr^' nhear i 



-H-" 




»y. «3 



P A C I F/ I C 



OCEAN 



117'15'3A""'6 15' 

TOPOGRAPHIC BASE M/ 

Control by USGS and USC & G 




Strike and dip of bedding. 
Strike of vertical joint. 



Landslide with direction of 
indicated by arroT. 



Fossil moUusk locality. 




LOCATION MAP 



. 20027 GEOLOGY \- 



CHAEL P KENNEDY. 1970 



ROSE CANYON FAULT ZONE 



ISM 




Ecoan« roeki undlfTsra 



STATE OF CALIFORNIA 

THE RESOURCES AGENCY 

DEPARTMENT OF CONSERVATION 



PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 

'9Si2'30" 




PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 

'96 |2'30" *97 ; ; i 760 000 



SAN DIEGO METROPOLITAN AREA a , 

BULLETIN 200, PLATE 3B 

117*00" 




GEOLOGY OF THE LA MESA QUADRANGLE 
SAN DIEGO COUNTY, CALIFORNIA 



by Michapl P. Kennedy and G. L. Pet- 

SCALE 1 24000 



contour interval 20 feet 
:d lines represent io-foot contour 
datum is mean sea level 

1975 

EXPLANATION 



Alluvium and Slopewash 

Qstc, Slopewfuh: Qai & Qno. Alluvium and i 



Landslide deposits 



Lindavista Formation 



San Diego Formation 



Poway Group 

Tp, Pomerado ConotomercUe: Tmv, Mission Vailey 
Formation: Tsl. Sladium ConglomeriUe. Co ' 



Granite rocks 



i of Ike eouthem Cali- 



Santiago Peak Volcanics 



Fault, showing dip 
(daehed where approximalely located; 
doUed where concealed; U. uptkr&wn 







r 






z 




















^ 


cz 


5 














y* 






c 




"'0 


s 


en 


^ 








" 




2 
> 




OPOGRAPH C BASE 
ConliolbyUSGSanc 








Fault, showing dip 

{dashed where approzimaleii/ located; 
' " ' ' ere eonceaie<' " 
: D. downlh 



dolled where eonceaied: U. uplhrovm 



Landslide with direction of movement 
indicated by arrows. 



Clay sample locality. 

Pit, quarry, or mine. 
Fossil coccolith locality. 
Fossil vertebrate locality. 




^^.. 




STATE OF CALIFORNIA 

THE RESOURCES AGENCY 

DEPARTMENT OF CONSERVATION 



PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 




PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 




GEOLOGY OF THE POWAY QUADRANGLE 
SAN DIEGO COUNTY, CALIFORNIA 



by Michael P. Kennedy and G. L. Pet 

SCALE 1 24000 






1975 
EXPLANATION 



Alluvium and Slopewash 

Qw), Slopewuk; Qal & Qni). ^Wt*i-iut. 



Landslide deposits 



Lindavista Formation 



Poway Group 

Tp. Pomertulo Conolof 

atone Tongue of Pomeru.. _ .. 

ion Valley Formaiion: Ttl, Stadium Co'Ujiomerate. 



Friars Formation 



Lusardi Formation 




Santiago Peak Volcanics 



8 I 

c - '2 
5 5> T 



'oximatelu located: 




CALIFORNIA DIVISION OF MINES AND GEOLOGY 
JAMES E. SLOSSON, STATE GEOLOGIST 



STATE OF CALIFORNIA 

THE RESOURCES AGENCY 

DEPARTMENT OF CONSERVATION 



PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 




PREPARED IN COOPERATION 

WITH 

THE CITY OF SAN DIEGO 



2H 

SAN DIEGO METROPOLITAN AREA (^3 

BULLETIN 200, PLATE IB p^ ^ 




GEOLOGY OF THE SOUTHWEST QUARTER 

OF THE ESGONDIDO QUADRANGLE 

SAN DIEGO COUNTY, CALIFORNIA 

by Michael P. Kennedy 

SCALE 1:24000 



1000 2000 



4000 5000 



Granite rocks 

UndiffereiituUed oranilic rocks of the aoulhem Cali- 
fornia batholith. 



Santiago Peak Volcanics 



Contact 

idaahed where approximatdy located: 
dotted where concealed) 



dTI 

Fault, showing dip 

{dashed where approximately located: 



CONTOUR INTERVAL 20 FEET 

DOTTED LINES REPRESENT 10 FOOT CONTOURS 

DATUM IS MEAN SEA LEVEL 



1975 
EXPLANATION 


i 


t- 

Zo 
en 


< 

1 
J 

c 

i 




Qsw 

Qal + Qsw 




Alluviui 

Qaw. Slopewath: Qal 
undifferejttiated. 

Lan( 


n and Slopewash 

d- Qsw. Alluvium arvi Slopewash 








Qls 






slide deposits 






Tmv 






Poway Group 

Tat, Stadium Conglomerate: Tmv. Mission Valley 
Formation. Conglomerate marked by circle pattern. 






Tf 






Friars Formation 






Control by USGS and USC & G 











I 



Contact 

(dtuhed where approximalely located: 
dotted where coTicealed) 



Fault, showing dip 

(dfuhed where approximately located; 
dotted where conceaied; U, upthrown 
side; D, downthrown aide). 



Strike and dip of bedding"^ 
in sedimentary rocks. 



Strike and dip of bedding 
in metasedimentary rocks. 



Strike and dip of joint. 
Strike of vertical joint. 



Landslide with direction of movement 
indicated by arrows. 




LOCATION MAP 



L^ 



GEOLOGY MAPPED BY MICHAEL P KENNEDY. 1971 



^ 


7*4^1 


u 


rf^S^Ji 


r 


A^T 


fel 


\^W