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SUBMARINE GEOLOGY OF
SANTA MONICA BAY, CALIFORNIA

by
Richard D. Terry, Stuart A. Keesling,

and Elazar Uchupi

A Final Report
Submitted to
Hyperion Engineers, Inc.
by the
Geology Department

University of Southern California

September 11, 1956

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TABLE OF CONTENTS

INTRODUCTION = #999999 9 rr rr rer eee esesses=

PREVIOUS WORK=22222<e<e2eees2%-e== eee me ee ee eee

Offshore Areaqnq- enn ener en ne nnn nner rena

Coastal Region—---- meen nna nn tren enn rena ana

Land Geolog Yorn nnn rt rr rt errr nna
GEOLOGIC AND GEOGRAPHIC SETTING OF

SANTA MONICA BAY---------- ------------9--------------

Introduc tion=9— 9999 9 en rr ras

Land Forms --9- 9-939 mn nn rrr rrr rr

Santa Monica Mountains -----------=---------

Santa Monica Plain----------------=--------

Ocean Park Plain-=--- -----2-- ---9-----"----

Ballona Gapowrnn enn enn nr rr rrr

El Segundo Sand Hills-----------~----------

Palos Verdes Hills---- e---- -2- 3-2-7 -------

SUBMARINE TOPOGRAPHY OF SANTA MONICA BAY------------

Submarine Physiographic Provinces--------------

Shel f -------------------------------------

Redondo and Santa Monica Canyons----------

BaSin Slope-nn-9 weet nn ra rer rrr rr

Santa Monica BaSin--------999-994------- =

APPARATUS AND METHODS-------------------------------

Laboratory Studies------------ eee poe enn eee

Mechanical AnalySiS<------- ---9--9- 7 -9n-

Calcium Carbonate------- ----- +9" -2--9-----

Organic Carbon ----- --- = --- 99-97-99

Mineral 0g y------- - on rn rr rrr nn

Sphericity and Roundness------------------

Rock and Gravel---------<9--9 99 tern

BOTTOM MATERIALS ---------------- 9 one nnnnn

Unconsolidated Sediments--- ---=--<--9----------

Areal Distribution of Sediment Types-----------

Sand, Silt, and Clay in the Sediments----------

CORRE TSE E CT

Fine Quartz-Feldspar Sand ----------------------

Description----------- 9-2 een nnn nnn

Occur rene C9 $n nn rrr

Rock-fragment Sand----------<-2----------------

Description--- -------- --- -- 2-2 enn

OccurrenCe@--- --- - -- -- rr rrr

Red Sand ---------- ----- <9 9 rr rrr

Description---------- -- --- een nnn nnn

Occurrence-- ------- --- on nnn

Shell Sand--- ------------- ------- 2-995 o----r

Description-------- ---- m9 29 ne nr

Occur ren @ == wn rn rr rn ren rr ren

Phosphorite-Glauconite-Shell Sand--------------

Description------- << -- - - ee enn nn n

OccurrenCe <99 99 nn rrr rsa

Glauconite Sand --<----------- ---9 99 r rer rr

Descript i0Nn---3-- <9 nn rrr re

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Median Diameters 93 ere nnn rrr rere rrr tenn 63
Definition and Significance--------------- 63
Distribution of Median Diameters---------- 64
Median Diameters of Sediments on Slopes
and Canyons qe <cere cere ren sora ries eam aime 72
Relation of Median Diameters to Depth----- 73

Sor ting 99 9 rn rr a rrr rena 76
Definition and Significance--------------- 76
Sorting of Sediments in Santa Monica Bay-- 79
Relation of Sorting to Depth-------------- 82

Calcium Carbonate-----------9---- +e eee 84
Origin of Calcium Carbonate--------------- 84
Distribution of Calcium Carbonate--------- 84

Organic Matter------3--<9- <= <2 $= en 88
Source of Organic Matter------------------ 89
Distribution of Organic Material in
Santa Monica Bayren-------9-- 9399-2 - 9-H 90

Cor CS -- nn nn rn errr rrr rrr ccs 98

ROCK BOTTOM AREAS ---- --= -9- = <= <9 = 27 - 2 22 ener 100

Rocks in Plac@------ 3-2-9 en en en rr er rr nn 100

Gravel -3~ 9-3 wn nn rrr rr renter 102

Phos phorit € -- -- -- -- wr en = err een een ann 105

Significance and Origin of Phosphorite--------- 105

Character and Origin of Nondepositional

Surf ace@S--— 33 = 9 er rr rr rer 109
Effect of WaveS~ +93 9-9-9 38n rer ee 113
Possible Effect of Tsunamis--------------- 114
Effects of Tidal Currents----------------- 114
Non-Tidal CurrentS------------------------ iLike)
Mudflows and Submarine Landslides--------- 116
Relation of Bottom Character to
Surface Current S---~ --- 3-999 r nnn an- ay

Conelwsi Ons = —— 3 owen eee eae a ae ee plate

SOURCE, TRANSPORTATION, AND DEPOSITION OF
SEDIMENTS IN SANTA MONICA BAY--9--- 233227 27 r2- 118

Source of SedimentS-=----- -----2-- 995 9------- == 118

Drainage Tributary to Santa Monica Bay--------- 122

Rete of Sedimentation=-----— -—=—— eee = een ee 122

Deposition in the Past Two Decades------------- 130

Submarine Landslides and Slumping-------------- 133

GEOLOGICAL STRUCTURE OF SANTA MONICA BAY-----------=- 13:5

Seismolog yr nn 9 en rn rn rr ern erence 135

Thickness of Overburden--------------<2--------- 139

Struc tur @ = 3 ta a nn rr rn en err 142

SUMMARY <9 = 29m tn rn rr rr rrr tran 152

The Geologic and Geographic Setting of

' Santa Monica Bayrnn----- enn nnn rr err rrr 152
Submarine Topograph yr--993 9-9 er en - ern r ren ¥§3
Unconsolidated Bottom MaterialSs---------------- 154

Relation of Transportation and Deposition
of Sediment to Discharge of Sludge into

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Areas of Rock Bottom--------------------------- 160
Bedrock --- --- ------ ----------------------- 160
Gravel-------------------- ---=------------- 160
Phos phorite------------------------------- 161

Geologic Structure----------------------------- 161

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TABLE OF ILLUSTRATIONS
Page

Major Land Provinces Adjacent to Santa
Monica Bay----------<<-----2-- ee ene nnn ee eee 10

Major Faults in Santa Monica Mountains along
the Northern Boundary of Santa Monica Bay----- 12

Drainage Area Tributary to Santa Monica Bay--- 17

Block Diagram of Palos Verdes Hills and

Adjacent AreaSe---------------------------- e-- 22
Submarine Topography of Santa Monica Bay-~----- 25
Fathometer Traces over Santa Monica Shelf----- 26

Shallow-water Fathometer Tracklines on Santa

Monica Shelf ------------------------ oe 28
Micro-relief of Santa Monica Shelf----------- - 29
Profiles of Redondo Canyon--------- eee cae a 38
Bottom Sampling Equipment used aboard the

VELERO IV---------------- eee Se
Location of Bottom Sediment Samples----------- 39
Detrital Sediment Diagram--------- Sbiesies wien eet ee CAS
Bottom Material in Santa Monica Bay----------- 45

Distribution of Gravel in Santa Monica Bay---- 48

Hypothetical Cross-section of the Rock and

Gravel Area----------- Sr - 49
Per Cent Sand in the Bottom Sediments-------- - 50
Per Cent Silt in the Bottom Sediments--------- sil
Per Cent Clay in the Bottom Sediments--------- 52
Distribution of Coarse Fraction Types -------- 54
Isopleth Map of Sediment Median Diameters----- 65

Cumulative Curve of the Percentage of Samples
in Santa Monica Bay----------------- ween ee nen 66

Graph of Median Diameters versus Depth------- - 70

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Sediment Sorting Coefficient plotted against

Median Diameter-------------~-------------- --- 78
Sorting of Sediments in Santa Monica Bay------ 80
Sorting Coefficients plotted against Depth----- 83

Calcium Carbonate Content of the Sediments---- 85
Graph of Calcium Carbonate versus Depth------- 87

Organic Carbon Content of Bottom Sediments---- 91

Distribution of Organic Carbon with Depth----- 92
Per Cent Organic Carbon plotted against Median
Diameter ------------------- ~~ - ~~~ ~~ - - 95
Lithology of Gravity Cores-------------------- 99
Lithology of Bedrock in Santa Monica Bay------ 103
Photograph of Phosphatized Mammal Bone------- - 106

Distribution of Epicenters in Santa Monica Bay 136

Probable Thickness of Overburden-------- w----- 140
Areas of Anomalous Seismic Data-------------- - 141
Geological Cross-sections ------ SA SSSeSeoRe6e5 143
Hypothetical Cross-section across Santa Monica

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SUBMARINE GEOLOGY OF
SANTA MONICA BAY, CALIFORNIA

INTRODUCTION

Marine scientists at the University of Southern California
began an oceanographic survey of Santa Monica Bay, California
in June 1955, utilizing the facilities of the Allan Hancock
Foundation for Marine Research. One of the major phases of the
investigation involved a study of the topography, geology, and
bottom materials of the sea floor. Interest in the bathymetry
centered around the need for locating regions which were
essentially free of significant relief, so that each submarine
outfall pipe could be laid without excessive excavation.

A study of the bottom material was necessary to allow proper
engineering design of the pipes, for the construction would have
to be accomplished on material ranging from rock and gravel to
fine sediments with appreciable clay content. It was necessary
to investigate the subsurface sediments, because significant
vertical changes in lithology are known to occur in short dis-
tances in shelf areas. Thus, borings, jettings, and cores were

taken to determine the nature of the subsurface material.

PREVIOUS WORK

When making a marine geological investigation of an area
such as Santa Monica Bay, pertinent information may be gained by
examining the geology along the adjacent coastal region. Sedi-
ments derived from mountains, the coastal plain, and sea cliffs

may be transported long distances before being deposited on the

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sea floor. Studies of the source area and the transport of
sedimentary particles therefore lead to a better understanding
of the sea floor. Also a knowledge of the surface and subsurface
geologic structures on land is helpful when attempting to decipher
the structure, phySiography, and history of the shelf area.

The literature dealing with Santa Monica Bay can be divided
into several categories:

A. Offshore area (including the shelf, but excluding the

nearshore zone) covering the subjects of submarine topo-

graphy, bottom materials, geologic history, paleogeography,

and structure.

B. Nearshore zone (including beaches and sand dunes)

covering the subjects of beach and nearshore processes,

and sediments.

C. Land geology.

In the following literature summary, an attempt has been
made to indicate the most important articles for each particular
phase of the marine geology of Santa Monica Bay. Additional

pertinent references are in the bibliography at the end of this

report and in the annotated bibliography.
Offshore Area

Blake (1856), although not describing Santa Monica Bay
specifically, made one of the earliest studies of the submarine
topography off the southern California coast. George Davidson
(1887, 1897) while associated with the U. S. Coast Survey (later
called the U. S. Coast and Geodetic Survey) gave the earliest
description of submarine canyons off the California coast.

W. S. T. Smith (1902) discussed California's submarine canyons,

but after this date little was written until F. P. Shepard became

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interested in them in the early 1930's. Three submarine canyons
are located in Santa Monica Bay although one, Dume Canyon, is
outside the area of this investigation. Shepard and Emery (1941)
described and discussed the various theories proposed for the
origin of submarine canyons, and covered in detail the submarine
topography off the California coast. Recently, Crowell .(1951,
1952) proposed an origin for submarine canyons using the Santa
Monica Bay area aS an illustration of his hypothesis. Clements
and Emery (1947) studied submarine topography in relation to the
distribution of earthquakes off the coast of southern California.

The earliest source of information regarding the character
of bottom material in Santa Monica Bay appears on “smooth sheets"
of the U. S. Coast and Geodetic Survey. The first reconnaissance
survey of Santa Monica Bay was made in 1851. However, detailed
work was not started until 1873 and was completed two years later.
There was additional work in 1893, 1925, 1926, 1928, and an almost
complete resurvey of Santa Monica Bay in 1933-34. Notations of
the bottom character were recorded on the “smooth sheets” in
connection with sounding operations. Bottom sediment charts
compiled from these notations may show an exceptional amount of
detail, e.g., U. S. Coast and Geodetic “smooth sheet™ no. 1341=B
made in 1875 for the northern part of Santa Monica Bay.

Trask (1931) made one of the earliest environmental studies
of sediments in relation to submarine topography. Most of the
samples he collected in Santa Monica Bay were located near Point
Dume. The results of his study have been quoted in numerous
articles and books dealing with source sediments for petroleum

and the origin of oil.

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The only previous quantitative studies of the sea floor of
Santa Monica Bay were made by MacDonald (1934), and Shepard and
MacDonald (1934, 1939). Approximately 200 bottom samples were
collected, from which 139 mechanical analyses and 27 heavy
mineral determinations were made, These writers also made
use of U. S. Coast and Geodetic Survey chart notations and, to
a minor extent, information supplied to them by fishermen. A
detailed study of the sediments, changes in bottom character,
interpretation of cores collected in the nearshore region, and
the source of the sediments of Santa Monica Bay were discussed.
The general results of this paper were summarized by Revelle and
Shepard (1939), and were used by Emery (1952) for interpreting
and comparing different types of sediments off the coast of
southern California.

Cohee (1938) described sediments taken from submarine
canyons off California including a few samples collected from
the canyons in Santa Monica Bay. Dietz and Emery (1938a, 1939b);
Dietz, Emery, and Shepard (1942); Emery (1941, 1947, 1952, 1954b,
1955)3 Emery and Dietz (1950); Emery and Shepard (1941, 1945);
Emery and Terry (1956); Shepard (1934, 1937, 1939, 1940, 1941,
1948, 1951), have contributed much information to our knowledge
of continental shelf sediments, areas of nondeposition, phosphorite,
and other important data on sedimentation off the coast of southern
California. Zalesny (1956) has studied the Foraminifera of
ante Monica Bay. Marlette (1954) in addition to a study of the
nearshore sediments in the vicinity of Redondo Beach, collected

several cores along the axis of Redondo submarine canyon.

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Gutenberg, Richter, and Wood (1932) made a special investi-
gation of an especially strong earthquake that took place in
Santa Monica Bay in August 1930. Corey (1954), Emery (1955),
have contributed to our knowledge of the structure, lithology,
and paleogeography of southern California's continental border-

land.
Coastal Region

Many articles have been written on various problems of the
coastal region of Santa Monica Bay. Some are technical, but most
are “popular accounts" of beaches, recreation, beach planning,
etc. Only the references which appear to be of some interest in
connection with the present investigation are included here, but
additional references will be found at the end of this report.
For a detailed list of all known references on the coastal as
well as the offshore area, and articles of general interest, the
reader is referred to the bibliography compiled by Terry (1955).

The most detailed and complete report of the beaches in
Santa Monica Bay was written by Handin 61949). Handin also
summarized several unpublished reports and included an excellent
bibliography on the beaches and source of beach sediments.

A number of papers have been written about certain specific
areas in the bay. Nicholson, Grant, Shepard, and Crowell (1946)
made a detailed study of the marine geology and oceanography for
a proposed yacht harbor at Malibu. Articles written about Santa
Monica beaches include: Anonymous (1917, 1933); Emery (1954b,
1955); Handin (1949); Handin and Ludwick (1949); Lapsley (1937);
Larsen (1939, 1942); Schupp (1953); and Shepard (1935, 1938).

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These papers concern beach erosion, littoral drift, the effects
of the construction of the breakwater at Santa Monica, and infor-
mation regarding the gravel beaches that occur along the Malibu-
Santa Monica shoreline.

A. G. Johnson (1935, 1940a, 1940b, 1940c, 1951) was interested
in the erosion along the Venice shoreline and made a special effort
to obtain records of changes along the shore. His reports and data
have been of great use in studying the nearshore zone. Anonymous
(1916) and Leeds (1916) also wrote short reports on the Venice
beaches.

The proposal for a harbor in the Playa del Rey and Ballona
Creek area has resulted in much information for that region. ‘The
U. S. Army, Corps of Engineers, Beach Erosion Board (1938, 1948c,
1948d, 1948e) has made a detailed study of the region, and the
Ue Se Wate rNayeRECpeninent Station, Vicksburg, Mississippi (1935,
1936) has conducted model studies of the Ballona Creek region.

The Los Angeles Regional Planning Commission (1938, 1940), Los
Angeles Department of City Planning (1941), and Stapleton (1952)
have written reports on the planning of the harbor, beach develop=-
ment, and recreation in the Santa Monica - Venice district.
Olsson-Seffer (1905, 1910a, 1910b), Purer (1936), Merriam (1949),
and Pierce and Poole (1938) have studied the sand dunes along the
Playa del Rey, Venice, and El Segundo region. Marshall (1934)
gave a description of the beaches at Manhattan Beach.

The Beach Erosion Board (1948b, 1950a, 1950b, and other
unpublished reports), Congressional Documents (1949-50b), and
Marlette (1954) have studied the Redondo Beach region, especially

in regard to the extension of the breakwater.

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Additional reports that are applicable to the beaches of
Santa Momica Bay include: Beach Erosion Board (1950a, 1950b),
which studied the beaches between Point Mugu and the San Pedro
breakwater; California Bureau of Sanitary Engineering (1943)
on the pollution of the Santa Monica Bay beaches; Grant (1946),
and Emery and Foster (1948) on water tables in beaches; and the
Beach Erosion Board (1948a), and Grant (1943) discussed littoral
drift.

A number of articles have been written about beach develop=
ment and shore line changes including: Chace (1953), Drury (1936),
Grant (1938), Grant and Shepard (1937, 1938a, 1938b, 1946, 1949),
and Griffin (1940).

Land Geology

Among the very large number of reports which deal with the
geology of the land adjacent to Santa Monica Bay are the following:
Bailey (1943): Woodring, Bramlette, and Kleinpell (1936); Woodring,
Bramiette, and Kew (1946); and Woodring and Kew (1932), who have
studied Palos Verdes Hills. Hoots (1931); Baily and Jahns (1954);
Durrell (1954)3 Kelley (1932)3 Pelline (1952); Place (1952);
Robertson (1932); and Soper (1938) have studied the geology of
Santa Monica Mountains. Vickery (1927a, 1927b) has studied
the physiography of the Los Angeles coastal belt, while Bailey
(1943); Cotton (1942, 1944): Davis (1931, 1932)3 Davis, Putnam,
and Richards (1930); Goldberg (1940); Livingston (1939); Place
(1952); and Wheeler (1936) were concerned primarily with the
uplifted marine terraces and physiography of the Santa Monica

Mountains region. Driver (1949) gave a summary on the origin

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and evolution of the Los Angeles Basin. Poland, Garrett, and
Sinnott (1948); Poland, Piper, and others (1945) studied the
coastal region, especially in regard to ground water. Reed
(1951) and Reed and Hollister's (1951) book on the geology

of California is an excellent source of information for
additional information on the geology of southern California;
and the recent publication by the California Division of
Mines, (Bulletin 170) of the geology of southern California
gives the very latest information for this region.

GEOLOGIC AND 3EOGRAPHIC SETTING OF
SANTA MONICA BAY

Introduction

The Los Angeles Basin is bounded by the Santa Monica
Mountains and the San Gabriel Mountains on the north; the
Pacific Ocean and Palos Verdes Hills on the west and south;
and partly by the Santa Ana Mountains and Puente Hills on
the east. The San Pedro and Santa Monica Shelves are sea-
ward extensions of the Los Angeles Plain. Most of the regional
faulting trends northwest-southeast, and numerous parallel or
en €chelon faults have resulted in the topographic prominences;
varying from mountains along the eastern border to hills and
knolls in the Los Angeles Plain area. The mountain ranges
along the northern border of the Basin are controlled by east=-
west trending faults.

Essentially all of the present major topographic features
in the coastal region, and probably much of the relief inland,

were formed by deformational earth movements during Middle and

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Late Pleistocene time. The hills and knolls in the Los Angeles
Plain area, the stream cuts, marine terraces and high sea cliffs,
and the great submarine canyons were probably formed at this
time. In addition, thick deposits of marine and continental
sediments were deposited over large parts of the region during
and subsequent to the Pleistocene.

Woodford, et al., (1954) have given an excellent summary
of the geological history of the Los Angeles Basin and a
resume of their report is given as follows:

\The Los Angeles Basin during Pliocene time was a marine
embayment somewhat larger than the present lowland area.
Its southwestern margin during most of this time probably
was a shelf, which though submerged, was thousands of feet
higher than the central part of the basin. The basin during
Miocene time was still larger, extending inland as far as
Pasadena and Pomona and merged into the Ventura Basin to
the northwest. . . During Middle Miocene time the basin was
bounded on the southwest by a land mass (Catalina) that
apparently was composed exclusively of glaucophane schist
and related rocks. Today the basin's central floor is buried
beneath at least 20,000 feet of Miocene and later sedimentary
rocks. The southwestern shelf has a crystalline schist floor
. . ethat is 1,000 feet above sea level in the Palos Verdes
Hills, mostly 4,000 to 10,000 feet below sea level north of
those hills, and as much as 14,000 feet subsea beneath Long
Beach. A similar shelf on the northern and eastern sides of
the basin is floored by pre-Upper Cretaceous crystalline
rocks. . .at depths that probably range from about 15,000
feet subsea to approximately sea level. The Los Angeles
Basin is somewhat similar in its geologic history to the
Ventura Basin. Each was a deep marine trough at the beginning
of Pliocene time, and each was then filled. . .with sediments
containing fossils characteristic of shallower and shallower
water, until the uppermost, largely continental, Pleistocene
strata were deposited .”

Land Forms

Santa Monica Bay is a crescent-shaped indenture of the
southern California coast with three major land provinces
forming its boundaries (Fig. 1). These physiographic provinces

are the Santa Monica Mountains to the north, the Los Angeles

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ti 3)

Figure 1. Major land provinces adjacent to Santa Monica

Bay.

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SAN FERNAN

LANDFORM

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“AL ANGELES

BOUNDARIES

ADJACENT

TO SANTA MONICA BAY

Smaller features

Simi Hills

Verdugo Hills

San Rafael Hills
Repetto Hills
Elysian Hills
Santa Monica Plain
Hollywood Plain
Sawtelle Plain

La Brea Plain
Downey Plain

+tMH OQ DOBBE RW

Mountains and other major land divisions

Baldwin Hills
Rosencrans Hills
Ocean Park Plain
Ballona Creek Gap

El Segundo Sand Hills
Torrance Plain
Dominguez Hill
Dominguez Gap

Signal Hill Uplift
Long Beach Plain

SUBDIVISIONS OF THE LOS ANGELES COASTAL PLAIN

MODIFIED AFTER

POLAND ET AL

1945 & McGILL 1954

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Coastal Plain to the east, and the Palos Verdes Hills to the
south. That part of the Los Angeles Coastal Plain nearest

to shore can be further sub-divided into the Santa Monica
Plain, Ocean Park Plain, Ballona Creek Gap, and the El Segundo
Sand Hills (Poland, et al., 1945; and McGill, 1954). Because
the topography, drainage, structure, and rock composition in
the provinces and sub-provinces have played an important role
in the submarine geologic history of the adjacent continental

Shelves and borderland, each area is briefly.described.

Santa Monica Mountains

The Santa Monica Mountains vary in elevation from 1,200
feet in the east to more than 3,000 feet at their western end.
The rocks in the mountains range in age from Mesozoic to
Recent and the sedimentary sequences total more than 26,000
feet in thickness. Many varieties of rock occur including
Slate, schist, quartz diorite, basalt and andesite flows,
tuffs, breccias, basaltic breccia, rhyolite, trachyte, sand-
stones, shales, and conglomerates (Hoots, 19313; Durrell, 1954;
and Bailey, 1954).

The complex structure of the Santa Monica Mountains is
shown on geological maps by Durrell (1954) and Bailey (1954).
The major faults in the Santa Monica Mountains along the
northern part of Santa Monica Bay are shown in Figure 2. The
Malibu fault trends east-west along the base of the mountains
close to the shore line, and crosses the coast west of Point
Dume and Las Flores Canyon. From available data (Bailey, 1954,

and Hill, 1954) it is believed that the Santa Monica Mountains

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tniot te teow pn wit geeaor> bee ‘ei ieee E
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Figure 2. Major faults in Santa Monica Mountains along

the northern boundary of Santa Monica Bay.

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have been uplifted and shifted to the west in relation to

Santa Monica Bay. Most of the other faults within the mountains
are small and probably have had little effect on the geological
history of the bay.

Except in the vicinity of Malibu Creek, the slopes of the
Santa Monica Mountains adjacent to the bay are steep and in
places form nearly vertical sea cliffs. The coast is irregular,
being cut by numerous canyons, and is quite rocky; especially
between Las Flores Canyon and Santa Monica Canyon. The beaches
from Malibu to about Las Flores Canyon are sandy and continuous,
but east of this point to about Santa Monica Canyon the natural
beaches are small. The earliest topographic sheets of the
U. S. Coast and Geodetic Survey, made in 1876-77, show narrow
sandy beaches extending from Point Dume to Las Flores Canyon.
From the latter point to Castle Rock the shore was mostly
rocky. The construction of the Coast Highway and the use of
groins has slightly altered the shore, but the beaches are
probably about the same as they were when the first surveys
were made. From Castle Rock to Sunset Boulevard, the old
maps show a beach about 75 feet wide, but from here southeast
the shore was rocky for a short distance. From this rocky
Shore to Santa Monica there was a continuous sandy beach.

Man has altered this part of the shore appreciably in the last
50 to 80 years. From Potrero Canyon to Santa Monica Pier the
shore is bordered by a nearly vertical sea cliff which varies

in elevation from 60 to 160 feet above sea level.

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Santa Monica Plain

Hoots (1931, p. 130) designated the south flank of the
Santa Monica Mountains as the Santa Monica Plain. Poland, et
al. (1945), on the other hand, restricted the name to the older
alluvial surface lying west of Beverly Hills. The underlying
platform was cut by marine erosion in Late Pleistocene time
and subsequently was covered partially by marine and continental
sands and gravels. While the plain and most of its deposits
are considered to be of Late Pleistocene age, the surface has
been modified in Recent time by erosion as shown by the broad
channels and gullies. Later deposition of coarse deposits has

partially filled the channels.

Ocean Park Plain

The Ocean Park Plain is part of the Santa Monica Plain
as designated by Hoots, but was restricted by Poland, et al.
(1945) to the region “whose surfaces is composed substantially
of marine deposits of Late Pleistocene (Palos Verdes) age,
and which lies largely in the south-west angle of Pico Blvd.
and Bundy Drive.” This mesa extends inland from the coast
about 3 miles, is 1-2 miles wide, varies in height from about
125 to 200 feet, and is relatively undeformed. The plain has
been divided into three smaller units by Poland: (1) a small
bench to the east, about 190 feet above sea level, (2) an
extensive central plain which slopes gently southward, and
(3) a ridge-and-trench area paralleling the coast, considered
to be Upper Pleistocene in age (Hoots, 1931). According to

Hoots, part of the western region consists of old sand bars

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and shoreline bluffs formed at a higher stand of sea level.
The material composing these old sand bars is a fine brown
thin-bedded sand that has been washed free of all clay

material.

Ballona Gap

Ballona Gap is a terrestrial feature of importance in the
study of Santa Monica Bay as large amounts of sediment have
been carried through it to the shelf and offshore region.
Drainage through the gap has probably played an important
role in the history of Santa Monica submarine canyon and per-
haps, to a minor extent, Redondo Canyon. Ballona Gap at its
narrowest place is 1.2 miles wide where it cuts through the
Inglewood-Newport fault zone, and is about 10 miles long in
its present extent from the coast to the east end of Baldwin
Hills. Bluffs up to 400 feet high were cut by the old stream
as it flowed between Baldwin Hills and Beverly Hills. There
is evidence that an antecedent stream existed on the surface
of Late Pleistocene (Palos Verdes) age before it was deformed.
The stream had sufficient eroding power to cut across the warped
rocks as quickly as they were uplifted.

The ancestral Los Angeles River which formed the Ballona
Gap cut a channel at least 50 feet below sea level at Ballona
Creek outlet, and 400 feet deep where it crossed Baldwin Hills.
Subsequent deposition of gravels am sands has filled the channel
at the coast and to a depth of 80 feet northeast of Baldwin
Hills (9 miles upstream). According to Poland, et al., (1948,

p. 51), the incised stream graded to base level substantially

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more than 50 feet below present sea level and possibly extended
as much as two to three miles seaward from the present shore-
line, presumably toward Santa Monica Canyon. According to
Layne (1935), the Los Angeles River was flowing through Ballona
Gap in 1815 and continued until 1825 (Kenyon, 1951) when a
particularly severe flood diverted the river to the south

where it joined the San Gabriel River emptying into San

Pedro Bay. Other extensive floods in 1862 and 1884 caused
part of the waters to return temporarily to Ballona Creek, but
since 1884 the Los Angeles River has discharged only into San
Pedro Bay (Troxell and others, 1942).

The mouth of the stream apparently migrated north and
south of the Ballona Creek outlet, for the earliest U. S.
Coast and Geodetic topographic maps show the natural outlet
discharging at the end of a long sand spit, while landward
of the split there was a salt marsh averaging about one mile
in width. In 1906 and 1908 the outlet was “fixed”, but in
1936 it was again moved 1,400 feet farther to the north.

At the present time Ballona Creek has a drainage area
of approximately 131 square miles from the southern slopes
of the Santa Monica Mountains and parts of Baldwin Hills
(Fig. 3). Since the construction of flood control channels
and other works by man, little detrital material is brought
to the bay through this course.

Probably the most important rifting in the Los Angeles
Basin is the Inglewood-Newport fault zone, which occurs in
the vicinity of Ballona Creek. Three faults which run

perpendicular to the old channel are associated with this

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fracture zone and are known in the vicinity of Ballona Creek.
From east to west they are: the Inglewood, Overland, and
Charnock faults. The latter two have only been identified
below the land surface, largely on the characteristics of

the ground water table. In each case, the western side of

the rift has been uplifted relative to the eastern block.
Poland, et al., (1948) points out that the transverse profiles
across Ballona Creek show that the gravels and sands within

the old stream channel dip to the south and frequently are more
than 40 feet thicker on the southern side of the channel. This
could indicate that a fault partly controls the stream channel,
and may also account for the relatively steep and straight
bluffs along the Ballona Creek escarpment. The circulation of
ground water does not indicate one way or the other whether

an east-west fault exists. However, as an alternative to
faulting, it is suggested that the stream migrated to the

south and as a consequence cut a deeper channel in this direc-

tion.

El Segundo Sand Hills

From the Ballona Creek outlet to Malaga Cove, a distance
of 11.7 miles, there are extensive coastal sand dunes which
have been termed the El Segundo Sand Hills (Poland, et al.,
1945). Merriam (1949) made a comprehensive study of the
structure, composition, and geologic history of the sand dunes.
She notes that the main part of the sand dunes ranges from
2.0 miles to 4.2 miles in width, while the active dunes, which

lie atop the main ridge, have an average width of 0.4 mile

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between Playa del Rey and Redondo Beach. The dunes range in
elevation from 85 to 185 feet above sea level, and have an
estimated volume of 36 billion cubic yards of sand. Vegetation
has anchored the dunes in many places so that today running
water and wind cuase only minor changes in their structure.
Lithologically, the cemented dune sands compare closely
with the beach sands now found in Santa Monica Bay. Subrounded
sand grains were found to be very abundant in only the larger
sand sizes and frosting and pitting, generally believed to
result from wind action, occur on about 5 to 15% of the grains.
The coarse sands appear to be derived primarily from a granitic
source. Reddish=-brown sands, similar to the red sands found
offshore, are common in the sand dunes; the color resulting
from the presence of iron oxide as a stain on the grains.
According to Poland, et al. (1945), Woodring, et al. (1946),
and Merriam (1949), a marine platform, correlated with the
lowest and youngest terrace in Palos Verdes Hills has been
deformed along the Newport-Inglewood fault zone as have the
sands of Upper Pleistocene age which were deposited on its
surface during a higher stand of the sea. After the deposi-
tion of this sand (Palos Verdes formation), a large region
west of the Newport-Inglewood fault zone was uplifted above
sea level. Nonmarine terrace material of Upper Pleistocene
age was deposited on this uplifted surface in the Palos Verdes
Hills and various places inland. There is some dispute as to
whether the El Segundo Sand Hills are partly offshore bars
(Eckis, 1934; Poland, et al., 1948) or wholly of eolian origin

(Merriam, 1949), Merriam concluded that the sand hills are

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composed entirely of eolian sands lying directly on the Palos
Verdes sand in most of the area, and that the sand dunes were
formed continuously as the sea regressed across the Palos Verdes
surface.

Zielbauer and Davis (undated) note that the Palos Verdes
formation in the Hermosa=-Manhattan Beach region is composed
mainly of sands and gravels which are similar to the overlying
coastal deposits, except that they occur somewhat farther inland
and include calcitic fragments. The formation is absent in
some of the region and its absence is attributed to marine and/
or fluvial activity. There is more or less continuous horizon
of relatively impervious deposits composed of silts, silty sand
Stringers, sandy clays, and clays that lie directly below the
sand dune and coastal deposits. This layer, called the “clay
cap”, is unusually flat, varying from 10 feet above sea level
to about 10 feet below sea level, and reflects the underlying
structure which consists of transverse drainage channels.

The clay cap feathers out completely at the present strand
line, and it is absent in a well 800 feet inland.

The drainage of the El Segundo Sand Hills (Fig. 3) shows
that only a narrow belt of that shoreline adjacent to Santa

Monica Bay drains into the bay.

Palos Verdes Hills

The Palos Verdes Hills, which form the southern and south-
eastern boundary of Santa Monica Bay, are a conspicuous uplift
along the southern border of the Los Angeles Basin. For the
most part, the hills have a relatively simple structure con-

sisting of broad gentle folds which from an anticlinal structure.

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There are few major faults, but those that do occur roughly
parallel the axis of the hills. The most important fault is
not exposed at the surface, but is a major structual feature
in the schist basement and the immediately overlying rocks.
This fault has been called the "San Pedro Fault" by subsurface
geologists, but Woodford, et al. (1954) have termed it the
"Palos Verdes Fault Zone’. According to Woodring et al. (1946)
the Palos Verdes Hills were uplifted with the San Pedro fault
(or the Palos Verdes fault zone) spearating the hills from the
Los Angeles Basin. This structural feature conceivably extends
far out into Santa Monica Bay (Fig. 4).

The exact age of the major faulting along the northern
border of Palos Verdes Hills is still unknown, but the zone is
probably still active. The strongest deformation in the
Palos Verdes Hills took place during the Upper Pliocene. Less
marked deformation during the Middle Pleistocene, and still
weaker movements occurred near the close of the Pleistocene
period. Deformation has been so recent along the northern
border of Palos Verdes Hills that the lower marine terrace
and its associated deposits have been slightly to moderately
deformed.

The basement rock is glaucophane schist and altered basic
igneous rocks of probable Jurassic age. Unconformably above
the basement rocks are several thousand feet of strata of
Miocene and Pliocene age and a relatively thin veneer of
terrace deposits of Pleistocene age. The rocks of Miocene
age are cherty, phosphatic, and silty shales, mudstones,

basaltic sills and tuffaceous beds. Pliocene rocks include

ile

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Figure 4. Block diagram of Palos Verdes Hills and

adjacent areas.

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Me AESess SETS

bluish gray glauconitic and formainiferal siltstones. Deposits
of Lower Pleistocene age are marine marls, silts, and sand,
while sediments of Upper Pleistocene age are mainly nonmarine
deposits.

The shores around Palos Verdes Hills are rocky with steep
sea cliffs. The beach sediments are mostly cobbles and only

occaSionally are there any small sandy pocket beaches.
SUBMARINE TOPOGRAPHY OF SANTA MONICA BAY

The bathymetry of Santa Monica Bay has been determined
largely from U. S. Coast and Geodetic Survey "smooth sheets”
numbers 4559, 4784, 5235, 5364, 5390, 5396, 5397, 5507, 5653,
5851, and 6259. Certain unavoidable errors were introduced
when contouring due to survey methods employed by the U. S.
Coast and Geodetic Survey. For example, most of the sounding
lines, especially those close to shore, were run along lines
parallel to shore. As a result, the exact position of the
constructed contours are not as accurately positioned as they
would have been if the sounding lines had been run normal to
the coast. Also, soundings were rounded off to the nearest
fathom, and the conversion to feet introduced more uncertainties
as to the exact position of the contours. None of the inaccur-
acies mentioned are critical and they become less important
with increasing depth. Additional soundings by the VELERO IV
were used only in the vicinity of the terminal ends of the
proposed outfalls and in the rocky area to the south of Santa
Monica Canyon. The data gathered by the VELERO IV indicated

no significant changes of the nearshore topography so that

a ae sone ster net omen i me _ 7 oe ee

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muit Yo soktieog: Thee. add | ; Sipes ' if
pt aa bore Lkteod, yterawann, or “ton Se srvosnes boss ”

‘or Aamion tirk ase’. bait ay chbesie ont 2b

Vaile. ehom beoubortak Steet of otazevo00 oa |
wawopedd: ons to enol ete 9
yet vest omens : Kee

VE OREJEV 9M? ed wanit ii Panolrtbba atgos :
eae 0 aba, ae oat Gis be cane ati

tals me eiaamsogar «

hee i ot i
eel i 4 I Darky

U. S. Coast and Geodetic Survey soundings were used almost

exclusively in that area.
Submarine Physiographic Provinces

The general physiographic divisions of Santa Monica Bay
are: (1) the Shelf, (2) Redondo and Santa Monica submarine

canyons, (3) the Basin Slope, and (4) Santa Monica Basin.

Shelf

For convenience in describing the submarine topography
and other portions of this report, that part of the shelf
that lies between the two submarine canyons is designated the
"outer shelf", or "central shelf projection”. The Santa
Monica Shelf extends to a depth of approximately 270 feet.

At this depth a pronounced steepening of the sea floor
indicates the shelf break. The width varies from a few
hundred feet at the head of Redondo Canyon to more than 8
miles between the two submarine canyons. North of Santa
Monica Canyon the shelf is very constant in width and the
edge follows the shape of the present coastline. From Figures
5, 6a, & 6b, it can be seen that the bottom slopes seaward
evenly and has a gradient of about 4 degree.

Nearshore, where sandy beaches are present, one or more
parallel troughs and ridges are often present. These long-
shore troughs and bars are generally transitory, moving up
and down in the nearshore zone and their presence, absence,
and position depend upon currents, storms, the tide, and wave

height. The shifting of sand, and even gravel along the bottom

xtearnegot solsandue ‘pile gard tes
Meds sat Yo taag Sant? ae

Pomitontona Yee ‘te

ated oat

ewe eee. war ‘Me aatheqone |
we g word iets atbbw oat

“eat ts asthe as taat ened peu Sheds say novned nom
ceils wont ni tesos ite od Ye saaran edt anes! ae

w200 20 th sande a8 “abitoasd (basa oxoabi axoaaiaait!
ea i 1

ramen eneet — mathe ote asgbls wae ave es cm

Figure 5. Submarine topography of Santa Monica Bay.

MONICA BAY

SANTA

e iy
Ww & . j
< =
2) i) pe
: foe
o
“A j j
cs) by
= Z|
4
ieee = \) is
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i,
ig

—s

,
L
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i)
mit
(aaa Arle

Figure 6. Fathometer traces of Santa Monica Shelf.
(a) Location of fathometer traces.

(b) Representative fathograms.

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ith

chit i
ean
i

n Ma
th i

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=

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May Cause pronounced but local relief within the nearshore zone
(Schupp, 1953). The shifting of bottom material in the form

of longshore troughs and bars is generally confined to water
less than about 15 to 20 feet deep (Shepard, 1950).

With the exception of the surf and nearshore zone, most
of the shelf is devoid of any significant relief. Small current
and wave formed ripples, marks, and burrows caused by bottom
dwelling animals may form mounds, depressions or undulations
a few feet high. However, these features like the bars and
troughs generally are not permanent.

A large number of shallow-water fathograms to 300 feet
were taken by the VELERO IV over the central part of the Santa
Monica shelf. It was observed that much of the shelf had
virtually no relief while other parts had significant changes
in elevation. Generally, the surface of any continental shelf
has small features consisting of mounds, ridges, depressions,
or undulations called micro-relief. Features about three feet
high are usually the smallest that can be determined by an
echo-sounder due to the motion of the ship caused by sea and
swell. Ripple marks and mounds formed by organisms are, there=
fore, too small to be recorded. A special study of the shallow-
water fathograms collected in Santa Monica Bay was made in
order to find the extent, type, and distribution of micro-
relief on the shelf (Staff, Allan Hancock Foundation, 1956).
Figure 7 shows the tracklines along which the fathograms were
obtained and studied, and Figure 8 shows the different types
and distribution of micro-relief which were then plotted along

the trackline. After all fathograms were examined and plotted,

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ve " bad Yess on? Ng soar + Ait ue ‘i aa a om VI, tLeie "ie

tonnes faa! Vea bait ertod voehtor ‘stky Wei tes cet (Lineal

| pelt tes ono eee

se peng AA a BAO a! tw narelaacs donitns? ema
a post ‘Soni iaeda evdlet aah Jab ooees i teed bins’ rok ta Lalo

| re vil poriandey ac ssn oat tepltnne aust ¥ t Lawed ate, i

ae sae m i Donte qi ite ic ae ow aed OY sath > venauees ea
| ergdt ae icin alle Ph fuaag? ainyan. baw ataasy ol Lye r
swat fads ott? Ae qua Ae aksoge A ibebaebos “vd od xs! gat *
ane: bait, enw NOS ep bio agent fee Be bien t Lod

TED ay negtudtst kb oan al ¢ tee Pcs ‘oie ——.

; { Aeog t

ee 2 ran

Me Ae p

Figure 7. Shallow water fathometer tracklines on Santa

Monica Shelf.

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[oak wokiom

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Wisk
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Ee vs 2 S
a tat

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Figure 8.

Micro-relief of Santa Monica Shelf.

three types of micro-relief were outiined: smooth, variable,
and irregular.

A wide belt of smooth topography extends from nearshore
to varying distances out on the shelf (Fig. 8). The only
distinguishable irregularities within this area are isolated
mounds a few feet high. Depressions are conspicuously absent
within the zone. Near the edge of the shelf, occasional well-
defined terraces or flat areas can be seen on the fathograms,
some of which can be seen on the topographic map of the bay
(Fig. 5 ), but little micro-relief is evident. An especially
well-defined terrace is present at the boundary between the
smooth and irregular zones and extends a short distance north
towards Santa Monica Canyon.

The zone of variable topography is generally seaward of
the smooth areas. The offshore limit could not be determined
accurately because of the transitory nature of the boundary
and the lack of fathograms in this region. Within this zone
are broad areas of no micro-relief and smaller sections having
low mounds, undulations, and small steps or terraces. Also
included in this zone is the sudden steepening at the shelf
break and the irregular topography associated with the sub-
Marine canyons. Along the edge of the shelf and the upper
part of the basin slope, are numerous notches, steps, and
small terraces. Closer to shore, north of Santa Monica
Canyon, are several gullies 20 to 30 feet deep which are,
perhaps, similar to those described by Buffington (1951),
and Emery and Terry (1956). Although there are many mounds

and irregularities within this general area, none compare in

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size and number with those in relatively rugged topography
of the irregular zone.

The irregular zone consists mainly of mounds and ridges
which project 10 to 40 feet and occasionally 60 to 80 feet
above the sea floor. The flanks of many of these mounds and
ridges appear jagged, irregular, and steep on fathograms.

The slopes may be locally more than 15°, but generally are
less than 1° or 2°. Some of the mounds are connected by low
ridges and these also have irregular and jagged sloping sides.
Individual mounds are 2,000 to 3,000 feet in diameter; some
are smaller or larger, but this appears to be the average
size. The area enclosed by the irregular zone is known to
have much gravel and some bedrock so that the relief evidently
is due to rock outcrops and patches of gravel. Because the
micro-relief chart is based only on fathometer traces and not
on bottom sampling, and because the fathometer does not
necessarily distinguish between bottom types, the limits of
the rock and gravel area differ slightly on the two charts

(Figs. 8 andi3.

Redondo and Santa Monica Canyons

The head of Redondo Canyon consists of an amphitheater-
like bowl which is located a short distance from the shore.
The canyon has a relatively flat floor throughout most of its
length, has only a few bends, and has a wide terminal end at
a depth of approximately 2,200 feet. According to Shepard and
Emery (1941, p. 64, pl. 12), the gradient of Redondo Canyon

decreases along its course; being 8% at the head, 2.5% at the

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pdaads owt ect ho plldehee te toPheb were) ts even bee soon at

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wornet) obacneh 40 snoboonp ast cosy em oe “a ae
MR Te ae Beek aati Pe Lil scold ieanieag #ab. :

outer edge, and averaging 4.1%. The axis of the terminal
end, like Santa Monica Canyon, swings to the south and appears
to terminate in a fan or delta (Fig. 9). The south wall of
the canyon generally is much steeper than the north side and
has local gradients of 25%. Two large tributaries are located
on the north flank of Redondo Canyon, whereas only small ones
are found on the south side. Shepard and Emery (1941, p.64)
compared soundings within the large tributary closest to shore
on the north side of the canyon. They found evidence that
recent soundings are consistently deeper than the soundings
taken about 50 years before which suggests slumping. Figure
9 shows cross-sections of Redondo Canyon taken at regular
intervals from near its head beyond its terminal end.

Santa Monica Canyon starts at a depth of approxmately
180 feet about 33 miles offshore. Unlike Redondo Canyon,
it has a Sinuous course, starting in a northeast-southwest
direction, turning slightly northwest, and then south at
the outer end. Santa Monica Canyon also differs from Redondo
in that it appears to be less rugged and complex, is more
asymmetrical, and has only small and few tributaries. The
average gradient along the axis of the canyon is 3%. Figure
6 shows fathograms taken across the upper part of the canyon.
It will be noted that the canyon has a "V" shaped cross-section
at the bottom but the north side flattens out forming the wide
north side of the canyon and part of the basin slope. A few

terraces along the side of the canyon are also conspicuous.

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ott Pebzeied ixt wor hate t este ttn earl bits tasias oneren |

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toy ott to: tae reaqu itt waetae gsaet enn gosta ewore *]

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wet A laats atead oa Yo tn9q bas novo ‘ott we ‘oota 4
Ge

even Regaatt 10 is a7 axe ROYABD ot? 30 shbe sets grote |

Figure 9,

Profiles of Redondo Canyon.

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Basin Slope

Off most coasts the continents are surrounded by a
continental shelf and continental slope. The continental
slope forms the seaward margin of the continents from which
the water depth increases to the abyssal sea-floor several
thousand feet deep. Off southern California, however, the
continent is separated from the abyssal sea by a series of
basins and ridges. The slopes bordering these basins are
called "basin slopes" to distinguish them from true continen-
tal slopes.

The basin slope in Santa Monica Bay is that part of the
sea floor seaward of the shelf and terminates on the floor
of the Santa Monica Basin. The average gradient is 5° sea-
ward of the outer shelf. The slope is broken into several
segments as a result of the two submarine canyons. West of
the outer shelf and south of Palos Verdes Hills, it is well-
defined, but south of Malibu and on the north side of Redondo
Canyon the basin slopes are partly the sides of submarine
canyons. Fathograms along the slope indicate a generally
smooth surface broken occasionally by small terraces or
steps. Profiles taken south of Malibu indicate that channels,

locally to 60 feet in depth are present.

Santa Monica Basin

A small part of the Santa Monica Basin can be seen in
the lower left corner of Fige 5. The floor of the basin is
relatively flat but deepens slightly to the west. Shepard

and Emery (1941, p. 64) believe that there is evidence of a

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| -phsioten 6 obiks gtx ith to sm to idan fod ay | :
| ‘tk epi Ve eine oath rete oy ‘pegote nian ooh . /
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%e: Mev ait ‘staat! xe etaedina se Ags ee
(oheanpite ‘Fett: Stas pee cde “ae by eee rsa? Spee

i ebmaet eit 'S 0 i) he,

submerged fan off the terminal end of Redondo Canyon, and
the profiles shown in Figure 9 confirm that a fan is present.
However, there are not enough soundings off Santa Monica

Canyon to determine the nature of its terminal end.
APPARATUS AND METHODS

Prior to collecting bottom samples in Santa Monica Bay,
U. S. Coast and Geodetic Survey “smooth sheets" and Shepard
and MacDonald's (1938) report were closely examined. Areas
where rock and gravel had previously been reported were
examined by rock dredges (Fig. 10-E) and in areas where the
type of bottom material was unknown or in doubt, an underway
sampler (Fig. 10-C) was used. Additional information regarding
the bottom character was obtained by the use of a shallow-water
recording fathometer, when it was found that extensive patches
of rock and sometimes gravel areas could be observed on fatho-
grams. After the general locations of rock, gravel, and the
finer sediments had been delineated, a snapper sampler (Fig.
10-D) or an Hayward grab sampler (Fig. 10-A) were used for the
collection of larger unwashed samples. In areas where the
vertical distribution of sediments was of importance, cores
(Fig. 10-B), jettings, and samples by divers were obtained.
Samples obtained by divers were limited to water less than
150 feet.

A preliminary determination of bedrock was accomplished
mainly on the basis of the "feel"* of the cable as the dredge
was Slowly towed across the bottom. Further criteria used

in recognizing bedrock included the freshly fractured aspect

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Mi Badsteg avieas xs jad} Bagel Kaw ot nt Uyeroan ined gin) tin 2 et
pene. rei by aSado ed bios dla open abet? em Cea oe Ww
\ ae, ergs beable: toes Bi) pRod tia ae Revenoy Haz tO7 1A nina |

ai) ‘mpiqase toraagre s atresia ead tod ari omkbee, tint)
‘aes tat, boew been tow (AROt Ry sataione savy tine all oe Ag, soot |
‘gate oraae Bao at a. Wawa roqzet bra) rottoalla |
#er08 ,nonadaoant 4) Haw, baMmNE bee iteay |
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dat past xodiew gz ‘bot hale Sten azavib wt vamiatga

bode tundoon bay toanbod ho franc tambo eee
in

agioat :
beet Biseth2o lhe | pmortod os ae
apedan % ts rat oat feat net

Figure 10. Bottom sampling equipment used aboard the

VELERO IV.

arn I |

of the rock, and if more than one fragment was obtained, the

similarity in lithology. Gravel and rock not in place, i.e.,

that had been transported, generally were determined on the

basis of dissimilar lithology, rounded nature of the fragments,
and the lack of fresh fractures. The dredge generally was

towed slowly from a region where no rock and/or gravel existed |
towards regions where bedrock or gravel was believed to be

present. At the first indication of striking hard bottom

the ship was stopped and the dredge brought aboard. By

repeatedly lowering the dredge and approaching the rocky and

gravelly areas from different directions, the general boundaries

of these areas were determined. Representative samples of bed=

rock and gravel were brought back to the laboratory for later

study.

Most snapper samples were obtained in conjunction with
hydrographic work so that a grid pattern was not used in
collecting bottom sediment. However, towards the end of the
Survey a number of samples were collected from sparsely sampled
areas. Material gathered by a snapper or the Hayward grab
were briefly described and placed in air-tight glass jars for
later physical and chemical studies in the laboratory.

Cores of bay sediment were split, briefly described
noting especially changes in texture, and placed in jars and
brought back to the laboratory for studies similar to surface
samples. Some problems associated with use of gravity coring
instruments have been discussed by Emery and Dietz (1941).

Their discussion of true core lengths versus collected core

length is worth notice.

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201 anal iduidal ‘beaut md beoaly bite Sediscenk VEekad 9

Oe r) si ng ven ve Denusedt ed

‘ROG

A gravity core sample is representative of all depths
penetrated, but the in situ depth of a given layer may be as
much as twice its actual depth in the core. The difference
between recovered core length and the depth of penetration is
produced by the thinning of sediments at the cutting edge of
the core barrel. Thus, the depths of penetration given for
gravity core samples in this report may be up to two times the
length of the core recovered. However, since most of the
sediment was of sand, or non-uniform sediment, the core length
was uSually almost equal to the depth of penetration. Since
it is virtually impossible to calculate the depth of penetration
because of the heterogeneity of most sheif sediment, the outside
of the core barrel was greased to determine the depth of pene-
tration.

Figure ll shows the location and apparatus used to collect

the bottom samples in Santa Monica Bay.

Laboratory Studies

Mechanical Analysis

In a typical sediment analysis, twenty-five to fifty grams
of sediment are washed through a 250 mesh screen with .061 mm
Square openings to separate silt and clay (grain diameter
less than .062 mm) from sand and gravel (grain diameters
greater than .062 mm). The coarse fraction is dried and
weighed. Gravel (grain diameters greater than 2 mm) is
separated from the coarse fraction by screening, and weighed
to determine its proportion in the entire sediment. Grain-

Size distribution of the sand portion of the coarse fraction

“et RotHG

Hetdete exot eroded" |

Figure 11.

Location of sediment samples.

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tiie: : sreddeninhte Sr Lab I Tid ase SEeat Hie:
rere metal sn opp emt tg) ai ; 7 dai ; i

(grain diameters between 2 and .062 mm) is determined using
the sedimentation method described by Emery (1938). Grain-
size distribution of the silt and clay is determined by the
standard pipette method (Krumbein and Pettijohn, 1938, p. 165-
170). The total weight of silt and clay is determined from
the pipette analysis. From these data the per cent of gravel,
sand, silt, and clay are determined and a cumulative curve of
the grain-size distribution is drawn from which the median

diameter and Trask's sorting coefficient were determined.

Calcium Carbonate

In a sediment calcium carbonate is considered to be the
material soluble in cold, dilute hydrochloric acid. This
value is determined by slowly adding the acid to a dried and
weighed sample until effervescence ceases. After this the
remaining sediment is washed with distilled water and any
remaining acid decanted off. The remaining sediment is dried
and weighed to determine the per cent calcium carbonate (dry

weight) for the entire sample.

Organic Carbon

Organic carbon content can be determined by the Allison
(1935) method of oxidizing a 500 mg sample of sediment with
chromic acid and the excess chromic acid back-titrated with
0.2 N ferrous ammonium sulfate. Under the conditions of the
determination, free carbon is not oxidized and carbonates,
being already oxidized, are not affected. Although this
method is rapid, convenient, and duplications check within

one per cent, it is not an absolute method because it assumes

“bonberes9d oT ~ sto " ‘

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ont elas voriA ,e0nees sbieoetvie} te Lid stumes be

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ott te anoke than: ont tobald ote thow jv dmomwa eaoxs9% 4
Lest emotes bia host bie eva ak nodzen: aot? cr :
BLax ‘Ayo oh TiA ‘baayatte tag hi: sooth ewan
matin dosiio "ano papi tau bad sashes

a nomiae ib

that all organic matter is in the same state of oxidation.
In addition, any ferrous ions present will also be oxidized,

resulting in slightly higher values.

Mineralogy

The percentages of heavy minerals in the sand fraction are
determined by heavy liquid separation using acetylene tetra-
bromide (C5H5Bry, specific gravity 2.96 at 20°C). Minerals
having a density greater than the liquid sink while those
lighter than the liquid float. Thus, two different groups of
minerals - the “heavies™ and "lights" - are separated and the
per cent of heavy minerals calculated. The heavy minerals are
then identified by standard petrographic methods. The light
minerals can be stained and identified using procedures out-
lined by Twenhofel and Tyler (1941, p. 131). Determination
of mineral percentages in individual samples is based upon
counts of approximately 200 grains.

The sand fraction (1/16 mm to 2 mm diameter) of each
sample is also usually examined with a binocular microscope
to establish sand types and to outline mineral associations

within various environments.

Sphericity and Roundness

Sphericity and roundness are two attributes of particle
shape. Roundness refers to the sharpness of the corners and
edges of a grain, whereas sphericity is a measure of the shape
of a grain as related to a sphere. The sphericity and round-
ness of sand grains are usually determined by visual comparison
of the grains with charts prepared by Rittenhous (1943) and
Krumbein (1941).

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? ; Notte bay vn aya, Pay

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Rock and Gravel

Hand lens identifications of rock types are made on all
gravel and bedrock samples from the sea floor. During the
identification of each sample, the roundness and sphericity,
nature of fracturing if present, and the presence or absence
of borings and encrusting organisms on the individual pieces
of rock are noted as an aid in determining whether they

represent a fragment of bedrock or rock in place.
BOTTOM MATERIALS
Unconsolidated Sediments

The distribution of the unconsolidated sediments of Santa
Monica Bay is based on the examination of 364 samples, and to
a minor extent on the notations of the U. S. Coast and Geodetic
Survey. The sediments are classified using a three component
system based upon gravel, sand, and silt percentages, as
shown in Figure 12. Because of the low volume of clay in the
shelf sediments, it is possible to include that fraction with
the silt and still retain the three component system. The
boundaries for the per cent gravel, sand, and silt fractions
in Figure 12 have been modified so that minor conponents
could not aggregate more than 20% of the sample. A sample
containing 85% sand, 9% gravel, and 6% silt is classified as
a sand. If it contains 76% sand, 17% gravel, and 9% silt it
is a gravelly sand. A sample containing 70% silt, 15% gravel,
and 15% sand is a sandy gravelly silt. Sands were further

subdivided on the basis of color into two sediment sub-types.

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ett f eee Formioqned A wy ‘de, ui aldhiie Etiam, deve vhke, eed
ano kta hie bots detae (reve sy Piso Voy pad soe gees oes
atnsneyaos) renin Tans GB fae? thom isd oved Oh sayeth
al game . ne signs. edt RO FOG tet 210 OF orngoruya. ‘ton |
Re bot tienat® a ities we bia douse ay eae #28 yoin
oh View: ye bye Ltyitny ms), hier sill eajabade cae .
van @e es ay vcibiainiieeadl n ybter.

Ries tis é yaaiebsa ony pome ‘ai

Figure 12. Detrital sediment diagram.

i1is AGNVS OQNVWS ALTIS

Lis
AT13AVEYD AGNVS| ATNSAVYESD ALIS

T3AAVYS
ALMS AQGNVWS

CUYAE DS:

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if
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Areal Distribution of Sediment Types

The least common sand sediment sub-type in Santa Monica
Bay is red sand (Fig. 13). This sediment is characterized by
an iron oxide staining of all organic (shells) and detrital
constituents. Red sand occurs in three small patches near
Hyperion, and in a narrow band off Palos Verdes Hills. The
sand at the latter location is coarse and contains abundant
shell fragments, whereas adjacent to Hyperion it is finer
and shell detritus are absent or rare. Similar sands have
been reported from many other locations off this coast and
Baja California, including: San Pedro Shelf (Moore, 1951),
San Diego (Emery, Butcher, Gould, and Shepard, 1952), near
San Nicolas Island (Norris, 1951), in Todos Santos Bay (Uchupi,
1956), San Francisco (Bache, 1852, 1856; Alden, 1956), and
south of Palos Verdes Hills in the vicinity of the Orange
County,and Whites Point outfalls during the present survey.
Additional data on the characteristics of the red sand will
be found in the section on “Coarse Fractions".

Olive green sand occurs in three small patches in the
southern part of the bay near Redondo Canyon; in a small area
near the Ballona Creek Outlet; and to a larger extent at the
head of Santa Monica Canyon. The sand at the head of Santa
Monica Canyon is distinguished from the other olive green
sand by the abundance of rock fragments, which are rare or
absent in the other areas. The greatest areal distribution
of olive green sand is in a zone extending from Palos Verdes
Hills to Malibu. This deposit is widest near Hyperion and

narrows to the south and north. The large deposit near shore

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; a val tea nebray eotet vie Tre hee: hte so Dieet |
Aiayods: antetios bas, pain, bb oF wets | “Wiha Ta bene
“eh eb # nse ot Ho et SS. weber siete E tede .
ave ea nest bene ot ie Hpssese: ie watshhh Aha bas’
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«bavdsu) yan! neteat ‘wohoT wk it ibe wth ret be “Sirs ek sy roo hh: nnd
‘(kee oeey x fap Ca (G2BL SOME Sito Soacawnia tl, a otek ;
- Senet oie te eeinialy ant et ei fer “eobaay OEE tes dines 7:
sowie oF nas pitt ae arheiine: enlot wos SEW sine tangd |
Ee Daina hey atv to eohtelyaicm yas, att, iad stam tenosT ERR
Pie Sewrlearewm 5 ae 2 uy Nok yee od tk pro ae
at ‘“ einloi'sa: iiame geal | ee ania be, com BELO,
Phe.) Live & ek Bh weno als ter duit or stot att i tg ovate
ot 1 save, araset sot tee 5 petano ine eno btw ‘edt 1828 | ;
Bete bea’ isnt eat vn: fers get RON? aatiaol shea’ % all
ok neha asire att moa) Wpile hregebradly ab ‘lana eri

pokswdkese $i leo. Heotn srs, aah, eR aneen oth ah ixoatall
raise! go. fail te wabtiaan oo ogy 08 mit cs baal PRP, atte v0]

Figure 13.

Bottom materials of Santa Monica Bay.

BAY

SANTA MONICA

BOTTOM MATERIAL

STATUTE MILES

~~~=300 FT. BOTTOM CONTOUR

ea ROCK
PSroaI

Ee SANDY SILTY GRAVEL
Fa
PS

Bi] RED SAND

| OLIVE GREEN SAND

ee SILTY SAND

i] SANDY SILT

WO hee

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a

grades westward into a zone of silty sand which extends from
Palos Verdes Hills to Malibu, but has its greatest areal extent
in the north. South from the city of Santa Monica to the
northern edge of Redondo Canyon, the silty sand is broken by
three patches of olive green sand; a large area of gravel and
rock; and is separated from the silty sand to the east by an
irregular band of sandy silt that extends north from Redondo
Canyon.

The silty sand in turn grades westward into sandy silt.
With the exception of an irregular zone that extends north
from the head of Redondo Canyon; this sediment type occurs
west of the silty sand where it parallels the topographic
trend of both submarine canyons.

The finest sediment type in Santa Monica Bay is silt,
which occurs in both submarine canyons and along the basin
Slope. A large area of silt occurs in Redondo Canyon in the
midst of the sandy silt. In Santa Monica Canyon the silt
extends eastward coincident with the topographic trend of the
canyon. In this same general area, a rather narrow tongue
of silt projects shoreward toward Malibu. The effect of the
topography on the distribution of this sediment type in
Redondo Canyon is not aS apparent as it is in Santa Monica
Canyon.

The normal decrease in grain size from sand nearshore to
Silt offshore is modified by the presence of gravel near the
center of the bay on the outer shelf. This grades into a

Sandy silty gravel near Santa Monica Canyon. With three

vals a 7 Bdiaon whee it eqs tintin ‘oat —

lbiea eas huge bas ony ng > snk ned) ia shinee. dake

i ae oat ney aad chon eit hit a

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% (5 zeea Seven se $i) meenrg outs s te a oun
we ote wobans abe : .

Seo dd: hw arog W280 icin wan’

exceptions, most of the samples outside the gravel area between
the two submarine canyons contain less than 50% gravel (Fig. 14).
Samples collected with the snapper sampler within the gravel
area generally contain less than 50% gravel, although those
near rock outcrops are composed of nearly 100% gravel. This
fact, in conjunction with the abundance of gravel in cores

and biological hauls, suggests that elsewhere in the bay the
gravel is partly or completely covered or dispersed with

finer sediments as shown schematically in Figure 15. In this
diagram, a asmouhetical east-west cross-section is shown

across the gravel area. The boundaries of the gravel area
indicated in the diagram were determined by dredging. Because
the gravel is covered in part by finer sediments which are

lost during dredging, the uniform distribution of the gravel

shown in Figures i3 and i4 probably does not actually exist.

Sand, Silt, and Clay in the Sediments

In addition to the other charts showing many of the
characteristics of bottom sediments in Santa Monica Bay,
contour charts showing the proportions of sand, silt, and
clay in the sediments are presented in Figures 16, 17, and 18.
The distribution patterns of these components are not dis-=-
cussed because they repeat information contained in other
charts, such as bottom sediment types (Fig.13), and only
tend to bear out and re-illustrate those conclusions. Their
Main use is as a reference to better visualize the nature of
the sediment in each portion of the bay. In this respect,

as the charts show. only the proportions of sand, silt, and

Figure 14. Distribution of gravel in Santa Monica Bay.

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Figure 15. Hypothetical cross-section of the rock and

gravel area.

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HYPOTHETICAL CROSS SECTION OF
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Figure 16. Per cent sand in the bottom sediments of

Santa Monica Bay.

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Santa Monica Bay.

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Figure 18. Per cent clay in the bottom sediments of

Santa Monica Bay.

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clay, they should be used in conjunction with Figure 14
which shows the location of samples containing gravel.
Gravel percentages were not contoured, as the samples with
gravel are few in number, and the extent of the distribution
is not as general or as well-known as that of the other
sediment components. In addition, much gravel apparently

is distributed over the entire bay at various depths below

the surface sedimentary cover.

Coarse Fraction

Properties of the sand fraction of sediments, such as
mineral assemblages, distinctive minerals, content and type
of organic remains, size, and shape can be used to gain an
understanding of the depositional history and source of
sediments. The sand fractions of all sediments collected
in Santa Monica Bay were examined with a binocular micro-
scope. From the mineral assemblages and distinctive minerals
or components, the following six distinct sand types were
established: (1) fine quartz-feldspar sand, (2) rock-fragment
sand, (3) glauconite sand, (4) phosphorite-glauconite-shell
sand, (5) shell sand, and (6) red sand (Fig.19 ). As the
classification into types is often based only on distinguishing
components, the areas of occurrence are not considered mineral
provinces, but rather as areas having accumulations of dis-

tinct minerals or mineral assemblages.

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Cyelorr ediqae: proksaw te bs autre vi Tie pat ehh eeey ef

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an. ene artienipea te istioast sien ght i sal aqugo nt | ae
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te, pais: ow balan i eas ogeds: iia casbe | ie eae, nionere., te,
) ‘edruow pee yseteis Lone toaegsh) SHE te ozbast era
imghed tox ettombhies ile to aan ka EY bags aa _wateeatk Bow |
7 kent tehunachth is daky necking as dad vom aningy staat ak
Miments eyirans PT RED tm 2: iyakuneeey TwVshka: at ney, cagone|
Verew eeqyt imen sonkveth thn gukwqituy, oat ER OOgMOD 100
jremgerttnatairs (5) , tee sieht ten ayy ‘wh +t} ‘boda Lede aiae
tietie ethane: Lg- 93 Luodasoily (hy: Bria we Pidoe ala (e) hee
enh aA; ae te. who) tven bes Ce) er yeti htode Ate,
ORE: ast aeenten eh 29g ithe sodas thkbaal
hers hom Sere ataneh Jo wa gamete: ie ewe. aut} 4 even
skp to. nies tadeinian.s gquived aiivun ee eodta Tog) weonked

spaldnsesk Lnarwel er to stash Yok

Figure 19. Distribution of coarse fraction types in

Santa Monica Bay.

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°
118307
T

ISA NTA MONICA BAY

{o} ' 2

STATUTE MILES
BOTTOM CONTOURS IN FEET

DISTRIBUTION OF
COARSE FRACTION TYPES

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SAND S

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Fine Quartz-Feldspar Sand

Description

The fine quartz-feldspar sand is a fine or very fine
angular sand composed primarily of quartz and plagioclase,
with orthoclase and heavy minerals making up only a minor
portion of the sediment. There is an average heavy mineral
content of 2.4%, and a range from 0.5 to 6.7%. The most
abundant heavy minerals are augite, hornblende, epidote,
biotite, and magnetite (TablelI ). Biotite is exceptionally
prominent in the offshore silts and sandy silts where it is
the most abundant heavy mineral in the sand.

The primary light minerals are quartz and plagioclase,
with quartz making up 49% of the fraction and plagioclase 42%.
Orthoclase averages 9%. The range of values for light minerals
are 49 to 60% for quartz, 30 to 49% for plagioclase, and 2 to
25% for orthoclase.

Authigenic minerals are rare. Glauconite, when present,
is restricted in areal extent and limited to amounts less
than 10%. Phosphorite occurs only in traces.

The most abundant organic constituent of these sands are
Foraminifera, which are present in all samples in varying
amounts. On the outer slopes of the bay, Foraminifera comprise
nearly all the calcium carbonate in the sediments. Here, the
percentage of calcium carbonate approaches the percentage of
detrital material until in some areas, the sand grades into
Shell sand. Other organic constituents of the sands are
Radiolarians, diatoms, and echinoid spines, which in all cases

are minor in occurrence.

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APA

Sediment Type

TABLE I

MINERALOGY OF SAND FRACTIONS
OF TWO SEDIMENT TYPES

Fine quartz-feldspar sand Rock-fragment sand
(ave. of 16 samples)

quartz 51.6%
plagioclase 40.4%
orthoclase 8.6%

Per cent of total sample of
specific gravity less than

269

augite 30.2%
hornblende 28.6%
epidote 15.4%
biotite 9.3%
magnetite 4.9%
zircon 1.7%
topaz ele

less than 1 per cent

chiorite
ilmenite
apatite

garnet
collophane
titanite
actinolite
fluorite
glaucophane
spinel

anatase

barite

kyanite
tourmaline
hypersthene
rutile
andalusite
glauconite
rock fragments
basaltic hornblende

Per cent of total sample of
Specific gravity greater than
2.9 3.6%

(ave. of 4 samples)

quartz
plagioclase
orthoclase

hornblende
rock fragments
epidote
magnetite
augite

less than 1 per cent

zircon
ilmenite
topaz
garnet
actinolite
tourmaline
hypersthene
enstatite

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The rounding of the detrital quartz, feldspar, and heavy
minerals of these sands is 0.1. Sphericity of this material
ranges from 0.70 to 0.80. Organic debris and authigenic
minerals are well-rounded and highly spherical. These
characteristics are inherent from their mode of formation.
Broken shell material is generally angular and exhibits low

values of sphericity.

Occurrence

Fine quartz-feldspar sand is the most widely distributed
sand type in the bay (Fig. i9). It covers most of the area of
the shelf and forms the major coarse fraction of the sediment
deposited in the two submarine canyons and on the offshore
slopes. Even in areas designated as glauconite sands, as much
as 70% of the sediment may be of the quartz-feldspar type, and
where the content of calcium carbonate increases by an abundance
of Foraminifera, the detrital mineral grains are mainly quartz
and feldspar. Again, on the offshore slopes, where median
diameters are small, the coarse fraction of the sediment is
generally fine quartz-feldspar sand.

The physiography of the shelf areas where this sand type

occurs is generally an area of smooth micro-relief.

Rock-fragment Sand

Description

This sand is medium grained, subangular and contains
rock fragments that generally are particles of dark schist
and fine-grained igneous rock. The rock fragments are acces-

sory, however, for the bulk of the sand is made up of quartz

eal.

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and feldspar. The average heavy mineral content of these
sands is 6.2% with a range of from 2.6 to 21.3%. The most
abundant heavy minerals are rock fragments, magnetite, horn-
blende, and epidote. Proportions of quartz, plagioclase, and
orthoclase show fairly constant relationships with an average
value of 50% for quartz, 49% for plagioclase, and 1% for
orthoclase. Foraminifera and shell fragments are present in

these sands, but are not abundant.

Rounding of the grains shows a wide range, with the larger

particles generally showing some degree of abrasion. This
characteristic is a distinguishing feature of these sands.
The range of rounding is from .10 to .60, and the sphericity

ranges from .70 to .80.

Occurrence

Rock-fragment sand occurs in linear patches nearshore
between the Hyperion Outfall and Santa Monica, and on the
north side of Redondo Canyon where it lies in a depression
trending north from the canyon. The largest occurrence in
areal extent is on the outer portion of the shelf at the
head of Santa Monica Canyon. This accumulation covers the
entire head of the canyon and extends south into an area
shoreward of the gravel and rock on the central shelf pro-
jection. Deposits of rock-fragment sand result in high median
diameters and in sediments which have 80% or greater sand

content.

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gather sha ne oe betes hea vieation *~” shea yi ‘ . D

Red Sand

Description

The red sands are coarse and subangular with a characteri-
stic red stain on the grains similar to that on the fragments
of some present day dune or beach sands. The mineralogy of
the red sand is similar to that of the rock-fragment sand and
the range of heavy mineral percentages is from 1.3 to 8.8%.

The red sands nearshore south of Redondo Canyon are
different in appearance from those north of the canyon. The
former characteristically have a brown color and a considerable
amount of shell fragments. In the northern portion of the
bay, a reddish color is more apparent and shell material is
generally minor in amount. Shell fragments occurring in both
areas show some signs of wear and the rounding of all frag-
ments ranges from .20 to .40. The sphericity coefficient

ranges from .70 to .80.

Occurrence

Red sand in the northern portion of the bay is always
associated with rock fragment sand where it occurs as small
isolated patches. It is nearshore in all cases except for
one occurrence where red-stained minerals were recovered
from the offshore deposit of rock-fragment sand.

South of Redondo Canyon the red sand occurs in a large
linear deposit which parallels the shoreline and lies close to

Shore.

i oe easier: sontin, oat, 2 SRI “ape Ba eu eh
‘base Tahrgast~ ino) wily a 40h ye Sakints. 2f),
1 ay ee a. ete BoM h) BL eset: % aynnke, Wy; ial
wan tox ca) £y ARON TO Nias Kpomsanon SRL
i ‘atone dD oh? Yo td eer] See noes 9 PRE Te a fps ae
“eidesobkarins & bie (20a apd @ ret wi Aoekt Pest aa wentey zoma0%
eB: ® Oo SoSH Gg westd2oh ody HPs Les owmpant Liens to taucms |
ai Seketan Phewe ‘bak Wipes skeen, Modan Re WOson ek psec is wed |

diod wi Rae eshowe! ints) fede indeme ne série yl texas |
1 j : : e)

feet ita te Sus hinray ot) te Bae lo Base Mirae! mone asta y
Sneks BLitsoa YPto tir4ay vy a. ae ae gina “ehesm!

“yt OS “amtin segue,

“pons 4 *
éyaw te ef: Yad iY OR Oe aa: Geo exit wit) 7h DASE bare |
i lea or gassed sh eratw bhes Hawa? daa ew Gat ane
pa tqnony eee tia. he S2One ae Be ee BO Oa Letatoe
bes svenee Sta ele lat. bes tg ghee ts ib eactte i onertwAne.

bias PrsGes a ioe ’faoded siredetioe eat

esebeg. Drmem Dog. © : ict vives | to ti08

et oe ee PHOS ap cit ad 1a um q ete ini 2 Hizogeh,

Shell Sand

Description

The shell sands are designated as those primarily com-
posed of shells or shell fragments with fine quartz-feldspar
sand as the host sediment. Sands with abundant shell material
and associated authigenic minerals are excluded from this
type. The organic remains, generally tests of Foraminifera,
are often broken. The roundness of the shells ranges from
210 to .40, depending on whether or not they are broken, and
the sphericity ranges from .70 to .80. The accessory detrital

material is angular.

Occurrence

The shell sands are limited to patches occurring at the
outer ends of the submarine canyons. They represent the
accumulation of shells as the coarse fraction of sediments
in offshore areas where the supply of coarse detrital material

is small.

Phosphorite=-Glauconite=-Shell Sand

Description

The composition of this sand is extremely variable, but

the association of phosphorite, glauconite, and shell fragments

is so distinct that it warrants classification as a type.
Quartz, mica, and rock fragments occur in the sand as detrital
particles in minor amounts and the average heavy mineral con-
tent of the sand is 2.5%. The minimum percentage is 0.6% and

the maximum is 6.7%, as glauconite and phosphorite generally

as hacia’ ut we bare
f aoaigt + maison Date

ptt ge gebrawb20 5 nontorrag n? bosieed? igh bare tt-adn oat

‘aa fume s2y97 ¥ of BAOY He ait brain: ons ‘ wines. 9100

“plat bye ‘Te Ket} neat eunang emt a gh toute te vo ita Lome

a a

Siivetan tha Abh gestions do kine eat ee hee siodetie® ak

“ohlgae ay

riak | iade~ot haugelOary orosqeadt

Hyd Oheahaey, ch bwninkaee Aa tthe reer Yo soit keoga ott
\eehemedtt iteds bag , eo tnoous ta , ot ¥ adil pany ie nobastooaean’ one
area’ 6 Rs bod ined dunn eh eRi wane Th: tanta yemiderd on

fetistoh eh bees of RE ‘game eter T / hoes, beg ok
ms 9 ‘betonke wor ord suerte. wily form adele aa ‘ronéw ad ak ,
Rei ASLO Wh, Shad aeeey’ wuakuie ait sth 5 ak bnee

pine | Ri Laver a at Svemeeorta, wins i eae uci ati an,

separate with the light minerals. The shell material present
has fragments of the larger shelled animals in addition to
the tests of Foraminifera.

The phosphorite shows a wide range of rounding (.50 to
»80), as do the smaller grains of glauconite (.70 to .80).
The sphericity of both minerals is from .80 to .90. Shell
fragments are angular, generally with rounding values of
-10 and a sphericity range from .70 to .80. Tests of Forami-
nifera which occur whole, are well-rounded. However, when the
tests are broken, their rounding is in the same range as that
of other shell fragments. Detrital minerals in these sands

are generally angular.

Occurrence

Phosphorite-glauconite-shell sand is found covering the
entire shelf projection between the two submarine canyons (Fig.
19). They are associated with the area of rock and gravel and
also occur as the coarse fraction of all the silty sand and
sandy silts on the outer shelf seaward of the gravel areas.
A small area near the edge of the shelf south of Redondo

Canyon is also covered by this sand type.

Glauconite Sand

Description

The proportion of glauconite in this sand type ranges
from about 20% to nearly 100%. Even though the quantity is
highly variable, all sediments in which glauconite is a

prominent constituent are included as glauconite sand. The

thE

a at

dam04 Pg sient OB: es Let ‘agen ype cae ig A ee o *,
‘sat widw aavengh ta ad ore Fs ene pies be ites Eaten area)

pnts as pees smal igh ne ak water peas notord avn ota]

-pbaae sands ak abavontm tule ed . fi rem i fode! ae Wi

pMelasne yt! axeeey pee

od gat tSvoD bow ah haee ft Lbetien be Linco tyne t ~ipel Lent)

_
el
il

wep tno eet PAT ce: itt jee it et ienelore btu che ouitag

bts totasy Ses thos To eete eee Ww Pegetigras ote Pads 8

Ree aaa Eis gr hielo monte Aro ody. ae wwo39 ola

(Pass soneen HS ep: Fie TTAte “satire adh 5 Kt ee whe

obhaotes ty Shedd ties se Aw sebe ot aha eo te bie

ooiet fede Shih vd te soten eats et ae

eee ih Wale Pe a

RoR? Se? he a he: a bob ai A to at #109039, wet
ab ye hinaap, ody Miia sane RODE einan@ 0d 08 suede
re S Oh y es isle ra rei ae ay: sesabbon, ta! :

1 4 Ree vt tis als

accompanying detrital material is generally fine-grained and
cannot be differentiated from fine quartz-feldspar sand. The
average heavy mineral content is 2.4% with a minimum of 0.9%
and a maximum of 4.5%. Shells and shell fragments included
in the sediment are generally the tests of Foraminifera.
Phosporite may occur, but it is limited to trace amounts,
probably because the sediment is fine-grained.

The glauconite is dark green to light brown in color.
It has a globular form, often with surficial suture-like
markings which allow recognition of either internal casts
of Foraminifera or coprolite casts. The glauconite grains
range in roundness from .70 to .80 and in sphericity from
-80 to .90. The associated detrital material is angular as
are shell fragments. Whole shells, on the other hand, are

well-rounded.

Occurrence

On the shelf and slope north of Santa Monica Canyon, a
large patch of glauconite sand occurs in which the glauconite
represents 20-30% of the material; the remainder being fine
quartz-feldspar sand. On the basin slope off the outer shelf,
glauconite sands virtually ring the entire area of phosphorite-
glauconite-shell sand. Here the sand contains the highest
amounts of glauconite and some of the sand fractions are
composed almost exclusively of this mineral.

A small accumulation of glauconite sand occurs along the
outer edge of the shelf and on the slope south of Redondo
Canyon. The sand on the slope has a low glauconite content

and is, therefore, similar to those sands on the shelf and

tens. owapaat aati ~ ane one
pakae soindounts ett pahag et htipage» zo # vee td

saa > etd radio ant mo yet Tate skedw ae Lge # 928)

- area ‘a ok veo wtoad. a dono sleek i! be Lede od, is

oink ‘noted AA Geko adt jbsbwetnes att> Li oemOe 3
fade: RPERO: ond, Yin eola hve sad ott Orne sagabisi-nds
ORs teri ea Ne oy onbe et one pits Elieurgayv 2 hea, on
| seoryal gate emhatacs ike Sed 9xeh . bees t toenba i ,

ee Oe, TO omoR Gas ee, Loose nig, ipa

slope north of Santa Monica Canyon. The sand on the shelf
south of Redondo Canyon contains a high percentage of
glauconite and is similar to the material on the slope off
the outer shelf.

The accumulation of glauconite sand is limited to the
zone of variable micro-relief on the outer edge of the shelf

and on the basin slopes.

Median Diameters

Definition and Significance

The median diameters of the bay sediments have been deter-
mined from graphs of the cumulative frequency by weight of the
diameters of particles occurring in the sediment samples. The
median diameter is the diameter of the central grain separating
equal weights of particles coarser and finer than the median
grain.

The median diameter can be used to determine the manner
of formation of a sediment as it relates to the strength of
currents which transport and deposit the individual particles.
However, transportation and deposition of sediments are
complex procedures with many variables, and the relation be-
tween median diameters and the agencies of transportation and
deposition are too little known at present to allow rigorous
analysis in this fashion. The main use of median diameters
is to indicate the relative size of the sediment for mapping
purposes, and for the determination of the distribution patterns
which can be used in conjunction with other components, such as
composition. In this manner, known processes in the ocean

environment can be related to the occurrences of different

tvpes of sediment.

seston tosnites st ni meme aatoa sig io te

ry “stavazore iis) miraitbeinn sh ji, okt ra ‘ ‘a
“aM nokta tee st betas eos BW a a Ruse. |

twonosis, wail te ee, weed a cont sister on? ous

_eiptomalh mt: hcl oni Aé.g3 ae,

Distribution of Median Diameters,

An isopleth map of median diameters of the bottom sedi-
ments in Santa Monica Bay is shown in Figure 20. In con=
structing this map, information from samples obtained with an
underway sampler was not used, as the finer portions of
material collected with this device are partially washed away
during the sampling process. Samples of sediment collected
while dredging for rocks were not used for the same reason.
Results of the analyses of cores were also not used for this
map. Elimination of the foregoing types of samples left 364
samples available for the preparation of this chart.

There are important limitations in the interpretation of

the contoured information in Figure 20. The first is that \
the contour interval is geometric, rather than arithmetic, \
using boundaries of Wootworth grade sizes as the contour values
(2, 1, $, a ete. mm)3 and, secondly, there is a decrease of i
the number of samples with increasing water depth. In Figure |
21 is a cumulative curve of the percentage of samples with |
depth which indicates the sparsity of samples at the greater
depths. Seventy one per cent of the samples were obtained
from the sheif at depths iess than 300 feet and the remaining
29 per cent was from depths greater than 300 feet. Thus, the
contours of the median diameters are based on successively
decreasing amounts of information with increasing depth.
Median Diameters of Sheif Sediments

Offshore on the outer sheif, median diameters are relatively
high and have an irregular distribution. This portion of the

Shelf contains extensive rock and gravel (Fig. 13) which are also

Figure 20.

Isopleth map of sediment median diameters.

een

ni
tat
i , "
1 a |
e I

YNOLNOD WOLLOB 14 O0E-----—...

S31IN 3Zinivis

€ 2 ! fe) '

WW NI YSLaWVvid NVIGSW
JO dVW H1L31d0S!

AVE VOINOW VINVS

oe se OE Bil

COMLORE: ==

fie
~
<3

=
#

PET tke ne re nana

PENAL I ERE Wt Sok Tye at seh wane one nee yiesase

Figure 21. Cumulative curve of the percentage of samples

in Santa Monica Bay.

——

) SeLhgaas to eye ta a09

SOEMOM u2 et

=
uJ
J
re
z
as
fe
a
uJ
(a)

fo)
2)

AN33583d SAILVINWNS

Lt A tsrmghs

contoured. However, these contours are based on only a few
snapper samples. Cores for foundation studies indicated that
the gravel extends a considerable distance towards shore, but
lies under the band of coarse sediment inshore from the gravel.
This coarse sediment is a thin cover, 6 to 10 inches thick,
over the underlying gravel. From the sediments collected by
a snapper sampler in the rock and gravel area, it is evident
that at least a portion of the zone has some fine sedimentary
material mixed with the coarser fragments. Due to the variabi-
lity of sediment in this zone, and the paucity of samples, the
exact sedimentary pattern cannot be completely defined.
Inshore from the central shelf projection, or the outer
shelf, the sediment is roughly banded parallel to the coast.
The outer band of sediment is coarse and extends along the
head of Santa Monica Canyon and across the inshore side of
the outer shelf. Shoreward from this is a pattern of finer
sediment extending northward from Redondo Canyon. North of
the tip of this deposit there are patches of fine sediment
which bridge the gap between the southern zone of fine sedi-
ment and a tongue of this material which projects towards
Santa Monica on the shelf off Malibu. This fine-grained
sediment covers most of the northern shelf, except for a
zone with slightly coarser fragments nearshore. South of
Redondo Canyon the sediment also occurs in bands parallel to
shore with very coarse sands close to the Palos Verdes Hills
Shoreline. To break this parallel pattern, between Venice
and Hyperion close to shore are several tongues of coarse

material which project seaward.

| takes end oul OE od. a never abe * ‘eh aoc htoea oases. ne |
(ian noite oat seve
taobive at th +BoRF covery bina sax a itr welqmae seqgane s

“a assatiog atnenthse eat tart

Whe tate bee Snk? stoe. Bat oeras ate Ae pris soq 6 baeel, a seat |

* esi $n¥ o4 ob .ahaseyert seeiens galt stew Po ae Entrstad |
‘ould eotqmae to yitovaq att baw aoe abate ik Seabee” Yn vat |

sbentted vistelqmes ad ones weetiiad (et em bee ‘¢oune |

i aetto na) to ~nokvowp ou Plode Lageesa: ott word snorteasy. ee 7
tage edt ot | botasd vi itu #2 Peni ben Sah ¢ Thee | 4
OOF nao ls shastxe bus se2zs09 ak Yaemebea Yo bees tha out?
ty Shit sxodend ett seevde tee govnns en kaolt ata te ned |
whigis ating ott
te. Aia9k, .fovnsD ohaobed nas yg rye LOR gritnstae trombone

i tank) te weetiao = 2) ahite nde besa sods

PeemiBer anli jo esdotet. san Guesd? Skuta ere? 1 dit, ot

ekbse sak? Yo aus maddie: ott seowisd’ gay itt onhind tem

Caivetin shiek ke orgaot a barn

ebynwet SIRS hog Ho Lite

bsakaaeomnh? Rise vebt Deke to? Liege mt ae. avkaoN. araak

6 20% FgeeRe Viteds ossdivan eae) te Peom REOVOO PME, : fh

ty ddnok ,srotieradn erunngart LsMOD vivagets it bs

oF Lollaszeaq ebnad gi eniiie ocls spemkbaa oa? nove nap
SLT aeabiey sola att ea Reeth: Sirae dich i i hake tbe
ontaey neswisd , ested ses ociasati afar danad | ot

aveoe 1 avugaos fuxewoe ah pangs. pt _paote

The gravels of the central shelf projection are relic
and were deposited during a lower stand of sea level. However,
the finer sediments occurring on the outer shelf are probably
a recent sediment cover. The coarse fractions of this finer
covering sediment contain authigenic minerals, such as phos-=
phorite, and abundant shell fragments possibly indicating
an environment of non-or slow deposition. Often this coarse
fraction material is in the size range of granules and pebbles
(2 to 64 mm in diameter). There must be sedimentation of
fine-grained material here as in other portions of the bay,
or at least over a portion of this area, but it ae be slow
enough to allow the formation of phosphorite and to favor the
abundant growth of shelled animals. It is also possible that
the phosphorite and shells are relics of a prior environment
and are now being covered or reworked. Then too, the topo=-
graphy of this area consists of small highs and depressions
of low relief (Fig. 8). Gravel and rock may be exposed at
the highs with sediment accumulating in the lows. The high
areas may be the loci of formation of phosphorite and the
places of growth of shelled animals which are subsequently
Swept away and added to sediment accumulating in depressions.
The coarse material at the head of Santa Monica Canyon
and on the shelf behind the central projection has been
identified from its coarse fractions as being mainly relic
sand with a low silt and clay content. This sediment is
probably an old nearshore deposit in which some silt and
Clay accumulated with the sand. The tongues of coarse

material nearshore in the vicinity of Venice and Hyperion

“ gndvaciint iidkeeog. a ste a Powtaw: te has ina

eR teoD, tink! ego .gok keegan ime ip! hehe T6 tmooraskvnS ti, .
Gaciad bon, ealwha tp Io. S300) HRD, ‘me seat tehxotsat nok tuaNT |
eto dekiarnemé bas, at Seem Svar het ar te, tent Pade bide i 1

res, ‘edt lo enottrceg. tonto) Ba alega ve some porkaamslet
woke ed Fp bk Died 2 wide te: soit te 5 olen.” nash te oy

| ‘ety sovat of haa “tk se dophshey te wo tac gate watts of dyna |
| “tons pidiaeog Gh Re) FT sotining botitgdd! i idtyrony Sanborn
, Sieeadatttrs tr ane '& tea Bok Ten ork ébeouts ove ota dqeadg ont |
nagot WEF tor gat?’ , beheoway 44 ‘ns sv0%, tee wor wa! ca

‘ eiok RasTde hy Aira a pat! aie ote 8 APN, means Rae to Tie

PaAchtaigee et ysm. Ae aah Lenya ie ele . BAS? Foks or won): 30ul
| Ayia iT: Jtwol ody od pnbre tains: Hiabhee tite ody. ait
outs Diss whkuodqaarty té fis ad aliens: ty kettey 2 ats ad | ek ag
Vitwerpsatves azn doidw elemies titrate Yo AHO 9g Yo! event
tno kamsiqed ea Shes whine (weastea of bebbas baw che
KORRES wD.cm eee es: “Yo hned! att 9s’ Ladyotam sRi8O9 ocr
aged. xed take dnt. © ag iwerdnsd: ade me ned Voids ont te
Siion tiitem BAPE BeGaght>ax) shang atk moad) partes .
‘ee Perse, Pee eat. at ats ag ge ee ike wed dul cst hyo

hn ¢r he Bees cotati te Be ciah nial outa natal te

also have coarse fractions which have been identified as
relic material. These are likely old beach ridges or near-
shore deposits associated with a rising sea level. The
intervening band of fine grained material which has a coarse
fraction composed of fine quartz-feldspar sand is evidently
sediment being deposited at the present time. This sediment
has either filled in a low area behind an older deposit
farther out on the shelf or has been deposited across the
variable topography of an older series of deposits formed

by an encroaching sea to create the smooth topography of

the shelf (Fig. 9). The inner shelf appears to be a
depositional apron, apparently formed by filling in of
irregularities and making a smooth plain since the last
lowering of sea level.

Fine material is kept from being deposited in the near-
shore zone by the action of waves. The patch of fine-grained
material near the Hyperion outfall, reported at this location
by divers, is probably due to the deposition of sludge from
_the outfalls, which is relatively rapid so that all of the
fine material cannot be removed.

Normal deposition of fine-and medium-grained marine
sediments is taking place on the shelf off the Malibu coast
and the median diameters decrease outward as a result. A
clue to the areas where marine sedimentation is taking place
at present is offered by a graph of median diameters related
to depth (Fig. 22). In the depth interval from 125 to 175
feet, which is the depth range of the band of fine sediment

on the central shelf, and also the depth range in which

NR I a RT A a

aonsten’ ahr "6 RRS dupe ahah aR | op ve Bitivonss Ree es ie seein
| Sadie ‘eebto, ner ‘pa keiaer Aaera wa * i heli he wats ‘eof

eat sisieiatl ba? beugee Fgh ie ae i panes: rot oO ate abaya

bems03, aeksoqeb) 20! sohuas: subd aa ay itgar gogos otdaknay jl

XO) yaiqe gnoged Aracura wih ena of ew gai como tomate xa
aad of riceggs Liwite wenn oe wee ood? dbsie ode :
Ay, Gl get let sof banks): braille ehoaan indott keoa st
bast! atid ODER BE REG toa: pe sabotage ne oir retwgomth |
ptever see Ly ackiswodil
+ be OBL oh bot bagTsh’ grind er 39 ist Bt Laetyvedten oak
ue Boakeia-enl? Jo Mateq edt |). cerew Fe Meboe one yd! anos “—<— '
nohtsoud ahatt fh) Kevacges Chetan ebesayN bA Sa08 Labeotin
ose we hese ho nor haere with a ae Kidatiot ek anys bbe
widt Yo tis doit os Giga vlaviterss ee fie kidei in
! hihiteiys if tesruad teases ae
ork Les bedbecden thom Hivesewl) iy noredooga TeRegn |
‘teased editim aap Pe, Rkdate. aah inc ane ld BASRRE ae asnont |
A Ovttokes Ba bikawebaie Bee ae eee eo Sh Dem Se

HOME UHL Ae st) Oe she aba ene ine ats wed sige #5958 ie hate

Figure 22. Graph of median diameters of bottom sediments

plotted against depth.

ao a Ho
ee

he doe
tea

HIGHEST VALUE

—

ARITHMETIC
MEAN

3L3aWITIIW

—
a
a
uJ
2
<
>
bE
2)
uJ
>
(e}
J

.008

DEPTH INTERVAL IN FEET

ait

material of similar size range occurs on the shelf off the
Malibu coast, the median value and the arithmetic mean of
the median diameters are almost identical. Also, the range
of values for this parameter are not extreme. However, the
values for sediments in other depth ranges are widely diver-
gent, where considerable relic material is known to exist
and where there are abundant organic remains. The effect of
relic material is not evident in the depth range of 125 to
175 feet as it is in all other depth ranges of the shelf.
This, then, is the depth zone on the shelf where sedimentation
is probably taking place at the present time and where this
Recent material has covered older deposits.

The coarse sediment occurring nearshore on the shelf
south of Redondo Canyon has been identified as relic red
sand which is possibly a submarine outcrop of the Palos
Verdes formation. This may be kept free of Recent sediments
by currents which flow from the center of the bay impinging
against the coast in this area or by the action of waves in
shallow water. The outer portion of this shelf is evidently
an area of deposition. The sediment there contains coarse
fractions of authigenic minerals and shell fragments similar
to the coarse fractions of sands on the outer shelf. Currents
Sweeping over this portion of the shelf may create conditions
of slow or intermittent deposition and a removal of fine-
grained sediment similar to that postulated for the central

shelf projection as discussed later in the report.

oN vravemolt

omoxted rn nares tae oF eoutay te
Apel ¢ishiw ate asia, sitaeb

‘tains ot Wwe the La Died an obi Widexoniauen. oxi witha
| a ook af watt ealeews ahaa Hieehinice o4R s19ah ened, ‘ban
iNet) Ded: te Sanat isqan gts ae, pebeve ton at Labvotam oktos

» tisda oat 4) Regie? iran hie Wie at eh tho ees tos) Oe
“‘tlolistnonibse o2erty \texta att ise sios: pat oid 2d, yea ett

aks waite, bite, owbs. seonielail ete ae ede hy poled ridugord a8]

whiesase iwike Dados eat Leta ore tral
trate ony ao nionedsen whet hOds top bs « a27 400 itt”

ber ailer ay ben iliwelbrt mead aml goyesd ohhober 46. 208

borhan ‘ent Bo eS hag, Sneha 8 Widitesd eh iby: pase
Neinahtss Tiayen Dey oot) esa ad yam einr uo tt aan} eebag

Boagnogak vad wit So xsaneh si es? wort mokuw dtmaeeune

nk envew t goktou oft Vd ee aias RLdS Fi deeod off Tanke ee

viinehies 2h ie he 22 elif My oharted xnetwo efT 4 sataw wal

ire hte aetah, do ase

S27 0od SERIO oxeelt dosmifex oaT

Selems & ermedaanl | thee ye tlavootm sigge tatu 20: dag ttom

ah 1
RIMS PUI ede Pele C82 BO HRMS to ate kT et seme pal

AOE ios steers Pan Wee, ont Io wohwsoq hes xev0: qnige

waite t te tsveinoa y ‘bas holt teogeD Ig ht bosch | cum woke, '

Lerties: aly yet eda Shae want pelimie tapmbbes. bos

ae Foils aie ity eb: Gawea! brie nak ga _pobtoatong

ie op rity

— -_ lo

On the offshore slope below the shelf, basin slope, ,there
is a fairly regular decrease of median diameters with depth.
Isopleth lines of median diameters usually show the same general
pattern as topographic contours. However, this pattern is
interrupted at places by small patches of sediment which are
coarser or finer than the surrounding sediment, which are the
result of slumping on these slopes. Emery and Terry (1956)
have shown that the topography of the basin slope of the Palos
Verdes Hills is made up of innumerable small landslide scars,
and that the sediments themselves on the slope and at the
base of the slope show evidence of slumping. The same pro-
cesses are undoubtedly active on the basin slopes and the
slopes of the submarine canyon in Santa Monica Bay.

The sand fraction of the sediment on the slope off the
outer portion of the central shelf is a phosphorite-glauconite-
shell sand, the same as the sand portions on the shelf above.
Thus, it evidently has been derived by slumping of material
or iS winnowed from the outer edge of the shelf. The same
sand fraction is present in the patch of coarse sediment in
the bottom at the mouth of Redondo Canyon. It is also similar
to the material occurring on the shelf above. Isolated
patches of fine material on the slopes may be areas where fine
sediment is building up under conditions of normal deposition.

The submarine canyons generally contain a tongue of fine-
grained sediment along the axes of the canyons. This is
particularly true in Redondo Canyon where fine-grained sedi-

ment lies close to shore in the upper end of the canyon. The

vig ay, i fr , a ily ha i ; i Chae Fr ; a " i
| oes aad aise aoveyeh set m Ragersiegot va penis

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v ig arriieteh Wont # Ot KO. aaetPyog wre ao em Hien elle 7 howe af ;
PRA Ri A: RET ha eS eRe eT haat Yee none wen ae ; a
ere ae ts an bits pike tie ‘ih gO Sage, GUT a9 + erie el 4
ab eco eto PRK) bib ddan if, eT Me Megaerg OF not sont "
Lhe Hate Bk hE ak abirnted lo sivem. sant) te wetted: ‘ort
bate bee. downity Pe hee tee: Ran weet twkentau ett
eich 3 wir eiha' aaant ee ht Beyots ot oo Le loot aaa io
9 bikeogen). £ aang 0 epee ryan ) ape ae ome Em a
Ee SPT wi aka Lies pray COTE R ove amen uct
ra) & fa) vhewReD ; Ret (A Se a Oa, nnd taomiton

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ae wa lesa Be) ane a us neq ody sik.

ere

water in submarine canyons below the surface of the surrounding
shelves is relatively quiet. Here, fine-grained sediments can
accumulate. Coarser sediments that are transported across the
shelf also have a tendency to accumulate in depressions such

as these canyons. Along the axis of a canyon, finer material
is often interspersed with coarse material that has slumped
down the canyon walls or has been trapped as noted above.

This is the case in Redondo Canyon (Fig. 13).

Fine-grained deposits in the submarine canyons may be
carried there by density currents. The axis of the pattern
formed by the median diameters in Santa Monica Canyon is
shifted to the north from the topographic axis of the canyon.
This may be due to the fact that the south wall of the can-
yon is steeper than the north slope, resulting in considerable
Slumping of material from the south slope, but allowing sedi-
ment to accumulate normally on the north side with a minimum
of movement by slumping.

The expected pattern of sedimentation on a continental
shelf, and to some extent on the steeper slopes at the edge of
the shelf, is that median diameters will decrease with depth.
This is due to increasing distance from shore, the source of
the detrital material, and to a reduced competency of trans-
porting agencies with depth. Thus, an ideal isopleth map of
median diameters in this environment should show them decreasing
with depth and more or less closely related to submarine topo-
graphy. Detrital material of sand size which is moved by

traction and saltation should show an offshore decrease,

_aweeita: beter: ida beagaee avec, yeas
Ce aah ty rte

weet oat te alxn one . -seneiy yhboo e sande meee

ek moraKD eokeoM ctiet ak dat | |

stloxnas ae) ag hme eiseargodot xt ut Liha “hehe ee bettate
sinks wee "to Liaw lidwos pat, +40 1 i wh ah s¢, vain &
suegnely OL A ciphiaute omineter ii wis mee: x8qorhe abe

fomtnin thw ohie avon Bee “ap eke o¢ yt ane ee oft

Pe Sa) Tee J mam wut

| | ‘BIORo) be auatenat9 spivey dog
Kntaeaktaes, B ixe nol ietasmbbon an WSs ong bar oes, pat

is. agus. HM te Raye tw aoueed a MIP Pavia Oe bans. ef

hepa: MT Roe gusexesh Ciiw eet eigia cai baw bane eh 3iode
to SER Oe wee Reo os) eomAteee jx hesetork wr) “pas ake

ipkseat he Toneregiee Dedies py ad tien. yh eva eee Laseuees

te ‘das abut ayn tw “es ittqeds Chiw ise

whereas silt and clay which are mainly carried in suspension
should increase in an offshore direction.

There are certain known factors related to the composition
of the sediment which will disturb this theoretical gradation..
These are:(1) the occurrence of authigenic minerals having
sizes Het related to depositional mechanics of the host sedi-
ments, (2) shells and their fragments occurring in a sediment
which are formed by local organic processes and bear no
relationship to the transported detrital components where they
occur, and (3) relic accumulations which were formed during
a previous depositional period, usually that of a lowered sea
level, and have not been covered or removed during subsequent
periods of sedimentation.

The distribution of relic sediments, authigenic minerals,
rocks, and organic remains in the sediments of Santa Monica
Bay often causes a general offshore increase, or a local in=
crease in grain size aS compared to the surrounding material.
The relationship of these factors to the general pattern of
sedimentation of the shelf and slopes is shown in Figure 23,
which is a graph showing the variation of median diameters
with depth. The diagram consists of the arithmetic mean,
median, and highest and lowest values of median diameters of
the deposits in each of a series of depth ranges. It should
be noted that the axis of this diagram indicating size is
logarithmic. The deeper depth intervals were made greater
than those at shallow depths to include a comparable number
of samples because of the decreasing proportion of samples

with depth as noted earlier. The arithmetic mean is the

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“oA | tamat Bh SBS aur k droite 2% her suns os bik, cae
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avai pmakb read bein hy moldy sae ons wstwoda iqaag a ak dake
¢ haem Bi toudy tos, ‘outt Ae ated eitos Wie ea ee te ert witgob,
to e1stemaih dedhem Woorawley Suswoh aus seedgkd been (ited
biworte +1 2988 Higal Ae aiptoas a te eons nb etheoqab a
i ak anke naditsbebed Ange a ial ts ekne ont, fasts baton
toteong ‘shmm aso: atavavdas sake regosd, oar cuba

sy medics ok | eh agus end ee rt Linnie wi hoa, ae Sood?

average and the median is the central value of all median
diameters in the depth interval. In each interval, the
mean usually becomes greater than the median as the spread
of values larger than the median increases.

The median and mean of median diameters increase with
depth in the interval from 25 to 100 feet. Also in this
interval, the values greater than the median are spread
considerably more than those that are smaller. This increase
with depth and exaggeration toward high values is due to the
fairly large amounts of relic sediment, particularly coarse
red sand, which occur in this depth range. From 100 feet to
175 feet the median diameters show a decrease. In the range
from 125 to 175 feet, the median and mean values for the
median diameters are almost identical and the highest and
lowest values show a narrow range. These depths correspond
to the most widespread areas of fine-grained sediment on the
shelf and the change of character in the curves indicates
present day sedimentation and contemporary covering of older
deposits as has been discussed in preceding sections. The
effect of relic material evident in other zones is not shown
in this depth zone. From a depth of 175 feet to 300 feet,
the median diameters show a general increase and a wide spread
of values higher than the median due to the occurrence of
relic material, authigenic minerals and rocks, and coarse
Shell fragments in this depth range. The coarse gravels,
indicated by dredging, cannot be shown on this diagram, since
complete samples were not retained for analysis, but their

effect would be generally to cause a high maximum value of

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i pane oy oaka tet ned iad ieee davrseind) eit) mk oot

oa besaqe O48 asthe ‘a0
. snonont abot sroldewe aod tna geaita seit som «ideo

PkIngr beni aeh etolage! poet bien te aidaora ee tala aH
ot raat NCE ec (egaes ahiab, eae Aine dod tw bia’ ba |
‘e3n07 oat a ss8ugsGeb ih We ki a9 Heid ex toon ott dood ev |

| gait Od Moulav wage her nek hoe one liad BYS oF eet nox? |

sty FRetere 9F. dag, \Leoatioins Showin 6rAa ot etomede nakoond
Saoney tien ‘sai qeh seott ‘OOM? WRUKOD 6 worle eon ter Teqwok|

“wae a0, dopmkbod ban huaat WARY, Tet eanwenm Putten) ws had Fae aa?!

staat’ aavane sty wk +otoai dale t ogardo ad? bas Ito
dab tebbaieeaerics Wak Lovbarlbensd oe ses Hott etmondthee {ab tae 1

wath beau owe guthosHxg ns Daaagoato sand ans ee a> eos
iets Pogo) eae “ERT ue Seve: Lake deo ok ton), to, toe tie

($09? QUE ot teed 29% Woo weqab & mest. cane Uihgeb wate

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Io! Pome Roe ONT ua! Be tal bem S19) ants) rondyla eowiay
wkssoo Dw (eee Baw efed ont Deo Kapa a tabeet ae phe
Stave p dence Set eaes agoh. eke yd atnengua? rt

gankis Clio Ah what ee One ay tetaed dau anoaah 4a votagk
ane ‘in ‘ai Laie 403 Senate sani aw patie: 5)

median diameter in this range and increase the arithmetic mean
while the median and low values would remain almost the same.
Below the shelf break the effect of slumping is clearly
Shown. The values show a decrease to a depth of 500 feet and
in this range there is still a wide range of maximum median
diameters. In the interval from 500 to 1,000 feet there is
a Slight increase in the median value and the mean shows a
sharp rise. This shows clearly the effect either of coarse
material which has slumped into Redondo Canyon in a zone of
generally fine-grained sediment and the median diameter of
the samples of this slumped material forms the high maximum
value in this range, or the possible effect of organic contri-
bution. At depths greater than 1,000 feet the median diameters
show a sharp decrease and the mean and median are nearly the
same. Also, the maximum and minimum values are evenly distri-
buted about the median. This indicates the existence of
normal sedimentation in this region without visible effects of
Slumping. Undoubtedly slumping occurs, but is out of the range
of delivery of coarse sediment from the regions of the shelf
near the break. The slumping is probably of sediments of
Similar size ranges and its effect is not evidenced by any

apparent anomalous pattern of distribution of sediment.
Sorting

Definition and Significance
The sorting coefficient (Trask, 1932) is computed from the

cumulative curve of grain-size distribution. By definition,

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Cie

the sorting coefficient is the square root of the ratio of the
particle diameter representing 25 per cent of the sediment
weight to that representing 75 per cent of the sediment weight,
or So = Qo5/Q75- It is, therefore, a dimensionless number
which is an index of the degree of sorting of the sediment;
or, in other words, the extent to which the particle diameters
are spread on either side of the median diameter of the sedi-
ment. The sorting coefficient indicates the degree of uni-
formity of grain size and numbers close to unity indicate
uniformly distributed grains in a sediment. In the system

set up by Trask, sediments having sorting coefficients from
1.00 to 2.50 are well-sorted; those with sorting coefficients
from 2.50 to 4.00 are moderately=-sorted3; and those greater
than 4.00 are poorly-sorted. A sediment having a sorting
coefficient of 1.5 is not twice as well sorted as one having

a value of 3.0, because the coefficient is geometric. The

sorting of sediments is directly related to the median diameter,

and in some cases, listed by Inman (1949), sediments having a
median diameter of 0.18 mm are the best sorted; the sorting
being poorer for sediments both larger and smaller than this
value. However, in Santa Monica Bay, the sediments with
median diameters from .05 mm to 0.10 mm are the best sorted,
even though the relationship holds that coarser and finer
sediments have poorer sorting. This relationship is shown in
Figure 23 which has a point plotted for each sediment sample
with the median diameter as the abscissa and the sorting
coefficient as the ordinate. On this diagram there is a

prominent grouping of points for well-sorted sediment in the

meters od? Ke’ “Seeing hoe & We an: bohudkeaekb cee
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| Pee a eon bias seaipede ent” he ‘sospmdi’ Hiab ant
‘* ad ‘otadt nasa tb anae nt), sean ito, |

Figure 23.

median diameters.

Sediment sorting coefficients plotted against

A
MOAye
ie .
On
Lary

Ceetahne bedtoia &

5.5

5.0

SLIN3IDSISIS3I09
9) 2 oO
t t oO

3.0

ONILYOS
x2 °

N on)

= 00

40)

10)

S00

MM.

DIAMETERS

MEDIAN

(rite
Ri

ji ldartapeblaee cat © Welter sevh bien er hpenilenjentartecmmmer ir FRR LI ote dota “

-05 to 0.10 mm size range. This range of median diameters
includes all the fine sediment of the shelf in the area which
has been interpreted as the zone receiving most sediment at
the present time. This probably accounts for the apparent
well-defined minimum grouping of sorting coefficients for
these sediments, for most coarser sediments in the bay con-
tain some relic material relating them to a previous stage

of deposition, and also contain authigenic minerals and shell
fragments. In addition, most finer sediments occur on slopes
where slumping and sliding of sediment take place and contain
numerous Foraminifera in their coarse fraction. These com-
ponents and occurrences would tend to indicate that the
sorting of these sediments is unrelated to the mechanics of
sedimentation which have caused deposition of the well-sorted
sediment on the shelf. It should be remembered that most
statistical theoretical studies deal with sediments from a
Single source which have been transported and deposited by

a Single uniform process.

The sorting of sediments in Santa Monica Bay is shown in
Figure 24. On the shelf, most of the sediment is well sorted
with small patches of moderately=-sorted sediment close to
shore in the vicinity of Venice, Hyperion and the Palos Verdes
Hills. Moderately-and poorly-sorted sediment occurs on the
central shelf projection and adjoining areas and at the
head of Santa Monica Canyon. Two relationships are evident,

(1) the moderately-or poorly-sorted sediments tend to

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eeavong: ay baw acai |
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eat ao Br ING see ondainialy boeiye any kaoog busy iotenahelt

HHS Os fr stisnssct ait owt raya 89 inom. asa

Figure 24, Sorting of sediments of Santa Monica Bay.

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OoOoOv7v< OS) LN3WIGSS s
G3LYOS ATNOOd 40 SvaUuV
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ONILYOS
Ava VOINOW VILNVS

be among the coarsest on the shelf, and (2) moderately-and
poorly=sorted sediments occur among the relic sands and
sediments containing an abundance of authigenic minerals and
shell fragments.

The nearshore relic materials, which are both red sands
and rock fragment sands, often contain significant amounts of
gravel or silt and clay. Both cause a wider spread of the
grain-size distribution and create the areas of moderately-
sorted sediment. The moderate sorting of these sediments
caused by gravel is inherited from their original period of
deposition. The sorting value resulting from the silt and
clay may have either originated during the last stages of
deposition, or as a result of the accumulation more recently
of a thin cover of fine-grained detritus over the relic
material. Moderate and poor sorting in the offshore sedi-
ments containing relic sands or gravels are probably due to
the same reasons. Poorly=-and moderately-sorted sediments on
the outer sheif have coarse fractions composed of authigenic
minerals and sheli fragments and a patchy distribution similar
to that observed in sediment size. Any processes which tend
to concentrate coarse material, such as winnowing away of fine
material or removal of this material from highs and subsequent
deposition in depressions, create “depression” sediments which
are poorly-and moderately-sorted, and "high"? sediments which
may be well-or moderately-sorted. The intervening purely
detrital sediments on the central shelf and those on the shelf

off the Malibu coast are all well-sorted.

bi
ale

vst een.

abies oat r8¥6 eetbarsy sonic fai hank
ames amin att, HE ankeaos 3605 bag eral

Areas of poorly-or moderately-sorted sediments on the
basin slopes below the shelf are more widespread than on the
shelf. Here the moderately-and poorly=-sorted sediments are
generally in the areas of the finest sediment. Slumping and
sliding are important here and probably are responsible for
the existing sorting. The accumulation of Foraminifera as
the coarse fraction of sediments may alter the grain-size
distribution enough to cause moderate to poor sorting. In
addition, silt and flocculated clays may settle out together,
and yet represent a wide range of particle sizes.

Sediment along the courses of the submarine canyons is
usually moderately or poorly sorted. This may be caused by
the movement of sediment through the canyons by slumping or
Sliding, both along the axis and down the side slopes.
Relation of Sorting to Depth

Figure 25 is a graph of the average and median of the
sorting coefficients by depth intervals. The variation of
the sorting of sediments with depth is similar to that of
median diameters. Generally, the arithmetic mean of values
in each depth range is greater than the median, which indicates
a wider spread of values toward poorer sorting.

A peak occurs in the curve in the 51-75 foot range where
patches of moderately-sorted sediment are located. From this
depth to 175 feet the curve is fairly uniform. This depth
range is over that portion of the shelf where most present-
day sedimentation probably occurs. Another peak is noted in

the 226-250 foot interval. This is due to the poor sorting

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gttgeb eka? eager aw, ehike? el) ovis eek tee ar .
tase eg Deon one, hiode ante 36) moi aq da 48
nk Daron ak Apa reittons Jasusoe Sarsind

Figure 25. Sorting coefficients plotted agains depth.

tga achege beiteta «

00S¢2-1002

00S1-I00I

MEDIAN

=
W
my
rs
é
Z
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fv
WJ
=
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x
-
a
uJ
(a)

ARITHMETIC MEAN

SNILYOS

in relic sands and gravels, and in sediments containing
authigenic minerals and shell fragments. There is a tendency
for the sediment to become better sorted at 300 feet which is
approximately at the shelf break. This may be due to turbu-
lence at the edge of the shelf which would tend to create a
better-sorted sediment. The curve is fairly uniform to a
depth of 1,000 feet and then has another peak due to the
relationship of poor and moderate sorting to fine grained

deposits on the outer slopes.
Calcium Carbonate

Origin of Calcium Carbonate

It is believed that all, or practically all, of the cal-
cium and magnesium carbonates in sediments are due to the
accumulation of shells. The examination of sand fractions of
the sediments from Santa Monica Bay indicates that the most
abundant organic remains are the tests of Foraminifera. How-
ever, in some areas, notably on the central shelf projection
and the shelf south of Redondo Canyon, fragments of larger
shelled animals constitute a considerable proportion of the
sediment.
Distribution of Calcium Carbonate

Percentages of calcium carbonate in the sediments are
shown in Figure 26. The percentage increases in an offshore
direction, being low over most of the shelf and slightly
higher on the offshore slopes. The exceptions to this distri-

bution are the extremely high percentages found in the patches

i
Hear

ma “e sides | bane % Aa as ‘dare sem
0 a ay tas nateckin att wba pase 0? » tum

Poeun, eee | ees ne -egore Kpearhaee
os. pay ag siete seater aie )

Figure 26. Calcium carbonate content of the sediments

of Santa Monica Bay.

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on the outer shelf between Santa Monica and Redondo Canyons.
This is illustrated in Figure 27 in which average values of
calcium carbonate percentages in each of a series of depth
intervals are plotted with increasing depth. The great
increase of the average percentage in the 201-300 foot
depth range is due to the large amounts of calcium carbonate
occurring in the sediments on the central shelf projection.

‘The high concentration of shells on the outer shelf is
due to (1) ecological conditions which are more favorable to
the growth of shelled organisms, (2) winnowing of sediment
finer than the shells, (3) the low supply of terriginous
sediments in this area, or (4) nondeposition in this area.
As pointed out elsewhere in portions of this report, this
region is probably an area of nondeposition or very slow
accumulation of detrital material. The main cause for the
increase in the percentages of calcium carbonate then is due
to winnowing or nondeposition of fine material. Since the
shells are relatively coarse they can accumulate in abundance
and thus constitute a high proportion of the sediment in this
area.

The high values of calcium carbonate on the shelf south
of Redondo Canyon result from the red sand which contains a
large number of shell fragments. This sediment is possibly
a submarine outcrop of the Palos Verdes sand, an Upper
Pleistocene age terrace deposit which contains a great
quantity of shell debris.

The general offshore increase in calcium carbonate in

the other parts of the bay is due to the diminishing supply

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yet, aber ab Relittommbaos. cad ee ee is E

7 vel, ww wai dina “a Leb aay taba tm ai
“amt a ote ehmnade n> nich aban 19 ) eaneaapreg itt ok vente
~— pou tanga aah te in to ahaa

oladteneg ak daaabbee abst
-soqql na huge patie ao bes es tp qoxotuo oe
Saudi» & ‘eniatana Hote taggin sonemey ‘og

)

Figure 27.

Graph of CaCO, versus depth.

Sle yg fA

AIN3983d

00Sc-I00I

OOOI-I0S

00S -IOE

OO0€-ISe
0S¢-10e
002 -IS|
OSI-101
OOI-IS
os-O

DEPTH INTERVAL IN FEET

of coarse detrital material derived from the land areas;
therefore, there is less dilution of calcareous material
offshore. Thus, the amount of CaCO3 is inversely propor-
tional to the supply of inorganic detritus at any point on
the bottom. The size of calcareous material is not dependent
upon currents and turbulence to the extent that terrigineous
sediments are, so that skeletal remains of sand=-size and
larger may accumulate where currents are very weak. Con=
versely, the coarseness of some of the shells allows this
material to accumulate where fine grained material cannot,
i.e., in regions of strong currents and turbulence. In
deeper seaward areas, shells (primarily the tests of Forami-
nifera) form the major portion of the coarse fraction of the
sediment, probably as a result of a small contribution of
detrital material which in other areas would normally dilute

the organic contribution.
Organic Matter

Almost all elements found in organic compounds are also

found in inorganic material. As a result, it is difficult

to separate pure organic matter. Since carbon is the princi-
pal constituent of organic matter, it is generally used as

an index of the amount of organic material. The abundance of
organic carbon varies between 50 and 60 per cent in organic
debris and if the total quantity of organic matter is desired,
the per cent carbon must be multiplied by an appropriate
factor which varies between 1.7 and 1.9. The choice of the

factor is difficult to make because the value depends upon

i Ad , oy San anaanioine
| ‘a tees ‘ott ett xiomita) mt pede ieee

a i oar a boas) PRABOD oft we no kineg vote att

Tle a eh i

| “ranks: ee n eludes a ak) wT OES
as rhoriig sit ¥ Redan ROWE! “ie ssa a

ovalvqasyge | it 0 both
ost te ooktis watt

the environment under which the sediment was deposited and
the type of plants and animals from which it was derived.
Furthermore, sediments containing appreciable quantities of
sewage may require an entirely different factor than those
given above. For these reasons, the per cent organic carbon
is used in this report to discuss the relative amounts of
organic matter, and these values must be multiplied by some
factor (such as the above) if the total quantity is desired.
Source of Organic Matter. The source of organic debris
in the ocean is both the land and sea. However, since the
amount of organic matter brought to Santa Monica Bay by
streams is negligible, it can be neglected. An important
local source is the sewage discharged into the bay, but the
most important source is phytoplankton which is the basic
nourishment of all life in the ocean. Only a small portion
of the organic material from the water survives the fall
through the water or escapes consumption on the bottom by
scavangers or oxidation. Sverdrup, et al. (1942, p. 929,
938) estimate that between 495 and 990 grams (dry weight)
per Square meter per year of organic production takes place
in the waters off southern California. Emery and Rittenberg
(1952) estimate that less than 1/16 of the organic matter
produced at the surface of the sea escapes destruction during
its travel to the bottom of the basins off southern California.
Trask (1939) suggests that only 2%, or 20 grams per square
meter per year of organic matter is deposited annually of an
original 1,000 grams produced near the surface of the sea,

and that under natural conditions sediments that have been

ae
ai tll

BP Oitganhsd: 192 tem w10 YD)
1 5 i ae sf Waid ue ; if iS:

re kee thet

Ry iv

> HO baer gre

i rae rou ay!
phaergye

buried to a depth of one foot, on an average, have lost about
15% in organic content. The rate of destruction varies accor-
ding to the rate of sedimentation. Thus, when deposition is
slow, oxidation can be almost complete,, whereas when sedimen-
tation is relatively fast some of the organic matter escapes
decomposition and is buried. This, of course, assumes that
there is an adequate supply of oxygen and that aerobic con-
ditions are present at the sediment-water interface in both
instances.

Distribution of Organic Material in Santa Monica Bay.
The highest values of organic carbon in Santa Monica Bay are
found beyond the shelf break and the lowest occur near shore
(Fig. 28). There is a general increase in organic carbon with
increasing distance from shore and with increasing depth.
Exceptions to the offshore increase are at the head of Santa
Monica Canyon where the organic carbon is low, and near
Hyperion outfail where it is higher than the average in the
nearshore region (Fig. 29). There is also a correlation
between the organic carbon and submarine topography; the
organic carbon being low in regions of elevations and high
in depressions such as Redondo Canyon.

The organic carbon content for 155 samples ranges from
0.13 to 2.76%, averaging 0.59 for the shelf and 1.52% for the
canyons and basin slope sediments. The overall average for
the bay is 0.96%. Emery (1954) reported that the average
organic carbon content for the continental shelf sediments
off southern California was 0.44%, and 1.56% for the basin

and canyon sediments (Table II). These values are similar

oil ara, sotyhe we hl paid: tnete

rR! oo & wath Ha roy tes, ‘ue iokged” ;
wnt! Retaeesewt nick cates ‘bm acre atrente ‘one

Figure 28. Organic carbon content of bottom sediments.

Oe Se

los|- GFF

TWAYALNI YNOLNOD 1.so

YNOLNOD WOLLOB 14 00€ —~—=

S3TIN 3inivis

€ 2 1 [-) !

INSLNOD NOSYVD DINVOYO

AVE VWOINOW VINVS

| __0e isa Oe. 8il SE DP

DU Yaast ne: Perauis Be

Figure 29, Distribution of organic carbon with depth.

RE RosC BING
ORGANIC CARBON

(2)
7)
>
<=
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ia
m
7)
+
>
at
O
ZL
W

4
e
=<
tS
AY
a.
mm f
1a 5
lt
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S
ipa
uu

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i

i news riverine aerate mal tenet amet ing melt yerilaaha ve
f hy i 4

-* va

Rah omens

BROS Nae Se ried 6
, — } a

93
TABLE II

COMPARISON OF ORGANIC CARBON IN SEDIMENTS
OFF SOUTHERN CALIFORNIA

Bay

Mainland shelves 0.44% 0.59%

(av. of 22 samples) (av.-of 150 samples)

Basin slope 1.56% 15526
(av. of 30 samples) (av. of 50 samples)

- Te

to those of Santa Monica Bay, suggesting that the effect of
sewage discharge has not appreciably increased the average
quantity of organic matter in the bay except near the outfall.

The distribution and quantity of organic matter in any
region depends to a large extent upon the movement and physice-
chemical nature of the overlying water, and the balance between
organic and inorganic deposition. For example, the main cause
for the offshore increase in organic carbon is the change in
the texture of the sediments in a seaward direction. This is
illustrated in Figure 30 in which per cent organic carbon is
plotted against median diameter. The diagram clearly illus-
strates that as the grain size of the sediment decreases, the
percentage of organic carbon rises. This relationship is so
well established that Trask (1939, p. 434), knowing the type
of sediment, has utilized empirical constants in order to make
rough determinations of the percentage of organic matter in
the sediment.

Detrital sediments and organic debris having the same
densities will accumulate together. In the regions where
sands predominate, i.e., in the nearshore zone, currents and
turbulence usually are strong enough to wash away fine silt
anc clay as well as organic matter which is fine grained and
is relatively light, so that it is easily transported by
weak currents. Even if large fragments of organic debris
were deposited in the nearshore zone, decomposition by
oxidation or bacterial action would slowly break down the
material into finer and finer particles which would probably

be washed seaward and deposited in quieter water. The large

by
:

tideree:

‘ye

;
Fa ow

Figure 30. Per cent organic carbon plotted against

median diameter.

oO
ae)

wadoma to oe

IN MM.

fac
LJ
be
LJ
=
<
O
Zz
=
O
LJ
2

se) aN)
INOS aD) SIINI\/ Sel) AUN BID), ta) Ble

a ee k i ‘4 ee
2 Eas MPnenremenee Nee i aces Oe ee aE eek

pore spaces between sand grains in the nearshore region allows
water to circulate with little difficulty and as a result,
oxidation of organic matter occurs to considerable depths
below the surface. The relatively low values of organic
carbon in the nearshore region, therefore, are the result of
an abundant supply of oxygen and associated bacteria that can
penetrate the sediments, together with shifting of sediment
by wave and current action. Such conditions facilitate
decomposition and transportation of organic debris.

Organic matter having a density slightly greater than
sea water can best accumulate in quiet waters where silt and
clay particles are also being deposited. Fine-grained sedi-
ment also aids the preservation of organic matter because it
is difficult for water to circulate through the small pore
spaces of silt and clay particles.

It is noteworthy that the proposed discharge location is
in the general region of nondeposition of sediments so that
there probably is considerable motion along the bottom. This
may have two important effects on the sewage: (1) redistri-
bution of the sewage, and (2) faster oxidation of the organic
matter.

The distribution of organic matter in sludge or effluent
after it enters sea water at the point of discharge will
depend upon: (1) the rate of flocculation or sedimentation,
(2) the direction and velocity of currents and turbulence,
(3) rate of decomposition, and (4) slumping and submarine
landslides. If the organic matter, largely in the form of

Sludge but also suspended in the effluent would flocculate

i” ‘pkaay20 to eoot ae ead ps i
to Hanoy at ome, : on oronat ean

“ptaybtton? acakstngd sow ‘ae
| Lindh atnagse 0 shoe: oktets

| oe $L2a ons thw sash ‘tatup me el t :
ie peadatarontd | bet ivogah sels vate ad vote

Risa Haine ots ityerornet? caniiane nk aotew aot htonk 5
eetghtrsy yen bis tthe ‘Yo! a

‘

pone ns as rey bade’ ur 4
+0 miat ane it elope. iottem obeny
afstoaoaty, Starg femur th ott, ae

immediately upon contact with sea water, the organic matter
would initially be deposited over a relatively small area.
Experiments have shown, however, that sludge generally does
not flocculate immediately, and being lighter than sea water
tends to rise.

Several observations have been made during a number of
experiments on the reactions of sludge in sea water; namely,
(1) sludge in the form of large “giobs” rises towards the
surface, but begins to disintegrate after rising only a short
distance, (2) after the “globs™ break up into smaller par-=
ticles there is a tendency for the smaller pieces to settle
very Slowly towards the bottom, (3) colloidal (and perhaps
clay size) particies do not always flocculate, but form a
residual turbidity which lasts in quiet waters for periods
in excess of 48 hours, (4) several experiments in which
Simulated thermoclines were used, indicated that the thermo-
cline may not suppress the rising organic matter below the
thermociine = apparently no matter how much temperature
difference exists between the boundary layers.

The tendency for the sludge to rise in the experiments
was due in part to the lighter density of the sludge, but it
was also probably due to gas trapped in the large "“globs”.
Once the gas was released by disintegration of the “globs",
more surface area of the sludge was exposed which facilitated
better flocculation. The above laboratory experiments may or
may not simulate actual conditions in the ocean; however, the
experiments did show the necessity of eliminating as much

grease and gas from the sludge as possible.

| at ‘abaswot ebay! eco eect "
= i vino gakets otha’ v9 Mik:
i oun ° “aad asians otnk qu ‘degnd: rede. ial oa ,
a sities of nevetg wadione ont ‘so yonsbast ‘s a ona
| egadaes bist) tabhotion Ch). me tod od ebuwwo? ein

# mnot ted ,ptsiasnoit acawde. Jot: oh eslodtieg ome

- ebotieg so) exatew teivp wk atmal, sisi yrthkdaos
Wey doditw mk ‘wigemkreqee Lexeves Oh) epstion BN fy.
momo pit tedt betes khoy ibe anew sanhseies

an Laneyal cynbiaed: on agowt ott niekne
etaomtzaqxs. odd th PaEx oF onbuke ott tot vonsbas?: ‘ iT
+h tud wabote’ eth%e wie ena rottigs t ‘od of aa ak

98
Cores

Coincidentally with the collection of snapper and
Hayward grab samples, a number of cores ranging in length
from 14 to 68 inches were obtained in several localities.

A total of 15 cores were collected along the proposed out-
falls and at the head of Santa Monica Canyon. A description
of the cores is given in the Appendix of this report.

Most of the cores along the traverse from Hyperion to
the edge of the shelf are uniform, but marked changes in
lithology occurred in some (Fig. 31). Close to shore the
sediments are generally composed of sands and silty sands.
In a few cases some shells mark the only vertical changes
in lithology. Farther offshore the sediments are predomin-
antly sandy silts, but gravel and other coarse sediments
sometimes occur. The two cores at the edge of the shelf
and on the basin slope contain sand and silty sands which
are overlain by gravelly silty sand, sand with shell frag-
ments, or by gravel. These cores on the outer shelf and on
the basin slope are therefore unique since they have abrupt
changes in lithology.

Two cores taken along the axis of the Santa Monica Canyon
(3342 and 3345) have gravel and sandy gravel, but the other
three are rather uniform in texture. Gravel, sandy gravel,
and shell debris are common in all of the cores taken from
the head of Santa Monica Canyon.

Additional cores and jettings were taken elsewhere in the
bay and close to shore, near Hyperion. An examination of

the logs show that the lithology varies greatly in a vertical

y : | venithiasot puke ak bentats
| xtap bevogerg sdt noite 2 |
“oktqizazed A snowad | a

1G peer obs iss.

“8 prode of sant IE) oe Sv

sien ose etnonibes arty rode. searant
ghvemkdoe sesnoo Ed sine Loveng te worth a
| Mone eits to sabe Sih. Fz | soxee ‘owt iT vate:
re ahese hhbe bias powe’ nkataon sorte setae odd |

eg at ben

est Shede dtkw ticen , hing yelie yitovexe td ixks |

pine :

no ban Made theo ect ao 29203: ‘some fevers xe ye 428

; y

‘sentto ont duet atevers yices bas foveaa vad c COREE | ae

; bee

been vbane Shahin aati! mh maot Lad beat ’ ous

Figure 31.

Lithology of gravity cores.

v¥ivery Yo yRolodtil

nis ES

1iis aanvs FE

Hid 3d

anvs Arts[_ |

SINIWOVES
113HS %
GNVS ALIS

1334 NI

GNVS ALTIS g
A113Av4u9 &

SLIN3NOVES
W13Hs [2
3 GNVS

QNVS

SIN3IW9OV YS
T13HS

HLON3AT 3405

13aAVvVYe9 Sees

ALIMIS AGNWS

13AvYNo
AGNWS Bass

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9)
=r
m
w

r
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AUTH
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AWE VOINOW VINVS

Nhs a
Nb v)
gee

5 he. bi) y

= ls a lke ania ih
worn neler

100

direction over most of the bay. Except for the uppermost few
inches, or feet in a few logs, most cores do not show good
core=-to-core correlation. It is obvious that great variations
in sedimentation have taken place over most of the bay. Some
of the factors effecting the sedimentation in Santa Monica Bay
and the significance of these changes in deposition will be
discussed after considering the geologic structure and the

source and transportation of sediments.
ROCK BOTTOM AREAS

The rocks of Santa Monica Bay can be divided into three
groups; rocks in place (or bedrock), transported rock and

gravel, and authigenic rock.
Rocks in Place

The rock outcrops rise as irregular and scattered mounds
on the outer shelf south of Santa Monica Canyon, and occur in
an elongated tract close to the Malibu shore as shown in
Figure 13. The Appendix lists the samples of rock believed
to be in place and describes their lithology. In addition
to the samples obtained during the present survey, Emery and
Shepard (1945) obtained a few samples of rock from the walls
of both submarine canyons. The U. S. Coast and Geodetic
Survey "smooth sheets" show rocky bottom along the Malibu
coast and off Palos Verdes Hills. Johnson (1940b) made a
detailed chart of the rocky (bedrock and gravel) seafloor in
the nearshore zone along the coast of Malibu and Santa Monica.

No rocks were dredged along this part of the coast during the

salt ‘t BASOS

pene, gaeud ocowaie oe ots seed maou 4 astqass 9

‘ehtaw 6a moe) aoe Yo welemns, wad a ‘benkstdo R80),
- ghtebos® tate tno 62.0) eR -bwoyass: ontiemdye
udiLail od anon, ttos tots yaaa. ‘wont Nedooia

101

present survey, but Schupp (1953) studied the gravel that
periodically washes up on the beach in this area so the
general lithology of the material is known.

Siliceous and non=-Siliceous shales were the most abundant
rocks recovered from the offshore area, followed in importance
by mudstones, siltstones, and sandstones. Emery and Shepard
(1945) recovered limestone and red rhyolite from Redondo
Canyon, and dredged conglomerate, rhyolite, andesite, and
granite from Santa Monica Canyon. They date the granite as
Jurassic (?) on its lithologic affinity to granite outcrops
in the Santa Monica Mountains. At least one sample collected
by the Hancock Foundation (station 4321) was positively identi-
fied as being Upper Miocene in age (Lower Mohnian) and several
other samples were dated as probable Miocene. Emery and
Shepard also found rocks containing Foraminifera of Miocene,
Pliocene, and Pleistocene age,in a conglomerate dredged from
Santa Monica Canyon.

A large amount of shale (both siliceous and nonsiliceous),
mudstone, and siltstone was dredged from the rock and gravel
area on the outer shelf. Many of the fragments were nearly
covered, or bored through, by organisms such as pholads and
echinoids. Few of the sedimentary rocks had diagnostic Forami-
nifera. Since pholads and most other rock boring organisms
are generally restricted to the littoral zone, or relatively
shallow water, where current and wave action is quite vigorous,
the abundance of borings indicates that this area was at one

time close to sea level.

> bans outed. xovengie sanctions eB) bated ona suigunen
“esnen0nM 6 arotinkmsro4 virkabet og Bide bave? oats

vitega sxbe! stnompes? eth We i Mena aetow ast

bis ebslosty #2 lowe: aime & es 30 wo sAgisonut: berod 20
Eraser okteongn thy Gad loon wu tenh bee ole Ao. wet

anekna yo yibret soon matte tem Pises iwenseses eons

102

One dredge haul (station number 3268) made on the outer
shelf contained schist. Since the fragments were large and
freshly fractured, it is probable that the dredge struck bed-
rock. This dredge haul was somewhat unique in that all other
hauls from this part of the shelf recovered only sedimentary
rock or well-rounded gravel. None of the gravel was composed
of schist, but occaSional small fragments of schist were found

adhering to pieces of shale.
Gravel

Most of the gravel on the shelf is well-rounded and
ranges in size from granules to cobbles. It is composed
mainly of igneous rock, but metamorphic and sedimentary rocks
are also represented. The Appendix lists the transported
rocks according to lithology, and Figures 14 and 32 show the
areal distribution of gravel recovered from the surface of
the sea floor.

Most of the sampling in the bay was done with a snapper
sampler which gathers about two to four cubic inches of sedi-
ment. The Hayward grab, used for obtaining biological speci-
mens, collects up to three cubic feet of sediment. The material
collected by both sampling devices appeared to have similar
characteristics, but after screening the samples obtained by
the grab, there frequently remained considerable quantities
of gravel which was not always recovered in nearby snapper
samples. Most of the gravel does not exceed a few centimeters
in diameter. Gravel is evident in the wash=borings made along

the proposed and old outfall lines shown in Figure 31. From

ie abet ele oabesh, edt ie ids
> ratio. can andd nk ouphan redwe

xeqqaria a lalate snob zaw yee att mk. gnitqnse ent. ‘to teoM
~kdo2 30 eotook otduo awet of ows twoda exettsg all
~koegqe taokgotoks gituteddo ot base date buswy el, sf?

Pt era sat «thpekbee Xe F462 aidus souls 0Ot w wioel :
antinke oved: ot bors eqge zenkweb aabignne dzod pai:

103

Figure 32. Lithology of bedrock and gravel in Santa

Monica Bay.

OC Sil

Sr6l wis
GuvVd3HS 8 AYSNA YILsVMWVLS 34000"

WLS 8VYD GYVMAVH o

“WLS YAIDNVS AVMYZONN & YAddVNS @

1Y3HD 9 SLVY3AWOTSNOD NO
IS NOIL3YDNOD
BNOLS3SWIT D1 A3NOLS3WIT S71

INSSIH LAY) 3LINOHdSOHd
SNOLSI1IS
ANOLSGNW
A1NVHS sno 3zoiis
31VHS
SNOLSGNVS
-VLIN WS J3NOLSONYVS
AG). Z1iyvNdD ZD 3LIZLYVNDd
aivis
LSIHDS VOIN
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JLINVYS
SSISND JLINVYD
LiIvsva
BLISSONVY NV SLITOAHY HY

G3LYOdSNVYL G dOYDLNO HS

aN a947
HNOLNOD WOLLOG 14 00€=~—

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Saw ZIIE(MIEVALS al

AQOIOHLIT ae
WE VYDINOW VINVS \ fe 7s

ore

|
oe
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rap

gecesi a

ite A a RA mh SANs soe iepeeete;

104

these considerations, gravel may be more widespread than is
indicated on the surface sediment charts, but below the depth
of penetration of a snapper sampler.

The gravel could either have been derived from outcrops
on the outer edge of the shelf or from the land adjacent to
the bay. The fragments are too large to be carried by present
day currents or waves in overlying shelf water, so they must have
been transported by streams or surf action in some previous
geologic time of lower sea level. This conclusion was also
reached by Shepard and MacDonald (1938, p. 213). The
restriction of large patches of gravel to the outer shelf
suggests that this may be the source area. However, the
great diversity of lithology of the gravel probably indicates
that streams carried at least part of the material from some
inland source having a complex geologic structure. Whether
the gravel was derived from erosion of the rock area on the
shelf or by erosion of the uplands and transported to the
area by streams during a lower stand of sea level is problem-
atical. There is evidence, however, that the gravel is a
relic sediment that was deposited in the early part of Recent
time or in the Pleistocene period (Shepard and MacDonald,
19383; Revelle and Shepard, 1939). The large size of some of
the cobbles and rock fraenente: abundant pholad borings, high
concentration of CaC0O3, and the attachment of coral and bryo-
zoans are taken to mean a long period of stability in the

Marine environment since the material was deposited.

Ain

| se oe at

“mt aro ania hadi aie, et, vom okst an:

a seteaatad reads: gent + es. caotonken Me ¥t Lesovkh

mos

ay moe) Laban wit iy Rout eae ks ti bud tan wate
wedton copa Rae S ad Hat iy Percy eae zai oorwae!
Sas m8 ozs does areal te oidoxs: wren bawiicals: ea foray
sae ot Pensryeonss them hea ait wy nokaaxs, a rr n
estes ae evat eon Yo te nee xeus 4 en cise ye
| wee Kepaah on? KGET? eee temant “ae dat ad: ek ort | bs:
‘\aiteson Ley Tre izes ald ; Wed eeoged’ eatte bane Soramd bee hf
sbinnedase tas Brags: iy ; ae oneoctere ha afl, at a0.
i mck Te halt wuans ‘ue x CREED. sbraqata bee others “Yue e
| May kat: «mgd ee bea hua Matec Stal ai Hoe bes ‘esrades 9 4
“eid tab Less te Hoviits Soha aah bane 1 ea 49 nobtash

105
Phosphorite

The only authigenic rock occurring in the bay is phos-
phorite. Almost every sample collected from the rock and
gravel area on the outer shelf, as well as samples from other
parts of the bay, contained phosphorite (Fig. 32). The phos-
phorite generally is in the form of nodules ranging in size
from less than 2 mm to more than 10 mm. Some phosphatized
mammal bones and shark's teeth were also recovered (Fig. 33).
Dietz, Emery, and Shepard (1942, p. 929) report that the only
shelves off southern California having phosphorite are off
Santa Monica and San Diego, although it is common on banks and
topographic highs far from shore. They report that the
shallowest sample of phosphorite obtained was from the Santa
Monica shelf in 240 feet of water, but one sample recovered
during the present survey came from 140 feet of water. This
may have been transported following formation, however.

Dietz, Emery, and Shepard (1942), and Dietz and Emery
(1942) have shown that the phosphorite found off the coast of
southern California is formed in situ by chemical precipi-
tation of phosphate from sea water. They also note that
Foraminifera of lower Middle Miocene age occur in large
nodules on the outer shelf in Santa Monica Bay, and in others
from the same general area there are fossils of Middle Miocene

age (Luisian or Relizian).
Significance and Origin of Phosphorite

Phosphorite forms by the chemical precipitation of tri-

calcium phosphate from sea water. The precipitation depends

leas eaoaiey nee i a cot 4 ahi asi ‘pr my Me oak pe
ae at) be: evonsx eat wen Ra | noe boa, eno %
oe ott tage damage, OM it pEeOn brains iia 3a

“Yo rp wy Prodgiedny dhVeit i ids tat pints ec, Voie
“baa! wined a0 mee ek ae Parent ss one ‘canis bisa arta

“pet tude taoges Waitt kes tie Mig an ake aitigh obngas

a eins? ot ont aa trypek 6 0 aan’ | W, stings : ow
; ‘derarooss otguan tints oe an pe ‘leat Dh ae Mana as

(eet a ta toa) ‘én ne) ‘sine Senne: saan | at yal
is A a tavonit HOR Ms er10! vere A ita bikapqeninss wad avait
peat: Bi 9 tte of MNO LD tiga bre eran. eared
ee reso: wat 044 haved): «Fz 1 cosh eM al Pay, swe ala oxad Ch
shaboere: tabbmsss OM ait Sy" Be Port of a fireeilt Eo t L
+sar atm Gals % oad eihaiee aie aoe sHadyeond to earl |
ngzat ne Sebi cee yet Per i othibay awit me! ntatinke f
azaitto aut ein ee wets bHe pacag nit Vieda soni. ba te

\ baa0hK mihi 2s, atinad? ones apni aoe jatsagy, ames ‘orth ;

‘an
| hhgisblaR: 70. Psy

oe ea FG 4

106

Figure 33. Photograph of phosphatized mammal bone.

i =e 72 ie es << a ——
= wus Siw, 7S Se

ma ee he ] we mi i ee A ga : ma

Se See ataealeta tai

DBO RO

107

upon the saturation of phosphate in sea water, which in turn
is a function of the pH. Apparently slight changes in the
physical=-chemical or biological conditions near the bottom
may cause a saturation of phosphate causing precipitation.
The formation of phosphorite is apparently a slow process and
consequently its presence indicates slow or negligible detrital
deposition in the region where it occurs. Since some of the
nodules in the bay area have grown to considerable size, they
must represent a reasonably long period of nondeposition. The
phosphorite generally occurs on the surface, not buried so
that its occurrence here is indicative of either nondeposition
or very Slow sedimentation

Most of the nodules collected by Dietz, Emery, and
Shepard contained a predominance of Foraminifera of Miocene
age, and at one station a mixed fauna of Miocene and Pliocene
ages. In several other samples, separate nodules and phos-
phatized cement of conglomerates contained Foraminifera of
Quaternary age. These authors concluded that while a small
proportion of the phosphorite must have a Quaternary age, the
bulk of the phosphorite was formed during the Miocene period.

There are at least two ways in which the phosphorite
could have formed during Miocene time and still be abundant
on the sea floor: (1) the phosphorite formed during the
Miocene on submarine highs which have been neither eroded nor
covered by later deposition, (2) the nodules on the present
sea floor may have undergone residual concentration from
Miocene rocks. Dietz, Emery, and Shepard (1942, p. 841) point

out some of the difficulties of both hypotheses. In the first

Anabmods od Like ton mk) aavoodt ae
at eH paw some ¥ bso aif ack

lea tt ane at Lepnsaiggr t teoe to anit bias age By,

108

case, they believe it to be inconceivable that the Santa Monica
shelf and canyons were eroded during the Miocene period. How-
ever, both the shelf and the walls of the canyons contain
Foraminifera of Miocene age enclosed in nodules, and Miocene
age rocks are on the shelf and probably in the canyons. The
second hypothesis = residual concentration of Miocene age
phosphorite nodules = perhaps is a better explanation, since
it would account for the abundance of phosphorite on the
Santa Monica shelf and in the wails of the canyons even though
each may have been cut in relatively recent time. Neither
hypothesis adequately explained the existing conditions; there-
fore, the authors presented two alternative possibilities to
account for the Miocene age Foraminifera in nodules of Quater-
nary age: (1) phosphorite deposits formed by infiltration of
phosphatic solutions into porous Miocene age formations with
the replacement of some of the Miocene age material, (2) the
phosphorite deposits may have been formed by enclosure of
reworked Miocene age Foraminifera in nodules formed during
the Quaternary. Thus, they tentatively conclude that possibly
the nodules dredged off southern California were deposited on
the present shelves, banks, and in the canyons during the
Quaternary and that previously an abundance of Miocene age
Foraminifera had been eroded or weathered out of the Miocene
age formations and concentrated on the sea floor surface
where phosphorite deposition took place.

No additional age determinations of the phosphorite
dredged from Santa Monica Bay have been made so that the

determinations by Dietz, Emery, and Shepard are the only

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109

ones for this region. It is known, however, that rocks of
Miocene age are on the outer shelf, and there is evidence
that most of Santa Monica Bay was formed in relatively recent

geologic time.
Character and Origin of Nondepositional Surfaces

From a theoretical point of view, there should be an even
gradation from coarse to fine sediment when moving from the
shore seaward. Numerous investigators, however, have noted
the common occurrence of coarse sediments near the outer edge
of shelves (Fairbridge, 1947). In addition, there are any
number of places where bedrock crops out on a sea floor which,
according to theory, should be covered by sediment. Many of
these areas of nondeposition are known off the coast of southern
California, so that surfaces of non-or slight deposition in
Santa Monica Bay are not unique. However, even though many
such submarine surfaces are known in many parts of the world,
little is known of their origin. There can be no question
that in most cases, sediments are transported at least as far
as the nondepositional surfaces, but then either by-pass the
surface or are deposited and later resuspended and carried
away.

The following criteria are used as evidences of non-
deposition: (1) rock outcrops exposed on the sea floor;

(2) gravel at considerable distances from shore. Gravel intro-
duced by streams cannot be carried far beyond the littoral
zone. In fact, gravel frequently migrates shoreward if it is

in the zone effected by wave action. Therefore, gravel in

yon ote) suede Hoke ebb al cee. oie xiao esy:
Y dost. oot? neds ag duo: eqns vouhoe saad esdalg to 38
F Shhnael paaaibee, we betsvos wd nla saiaicall ot gn

nee ea atae cove wont caikghxe abot + ene ae
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Pcmictinad bes. Tame ptrese weteh Dee aati sts oe oO

reasek Cerety , esoste: ea) osoaor ehh s 9.

110

deep water probably represents a deposit laid down in the
geologic past; (3) The occurrence of rocks bored by organisms
gives strong evidence of a littoral or shallow water environ-
ment at the time the rocks were inhabited by animals. If the
depth is now considerably greater than the depth-habitat of
the boring organisms, it must be presumed that sea level has
risen and that little sediment has subsequently accumulated}
(4) the presence of coarse terrigenous sands separated from
the shore by finer sediments probably indicates at least two
periods of deposition; (5) the presence of glauconite, phos-
phorite, and high percentages of CaCO3z are indicative of slow
or no deposition. On the other,hand, much of the area in
Santa Monica Bay which exemplifies the above criteria also
has up to 30% silt and clay in the sedimentary material.
Deposition, then, does occur, but is either extremely slow

or is intermittent with a periodic resuspension of the
material.

As pointed out by Fleming and Revelle (1939), and Revelle
and Shepard (1939), the primary force necessary to transport
sediment is the “static bottom friction" on sedimentary par-
ticles. If some force lifts a sediment particle even for a
brief moment, then any resultant force (current or turbulence)
acting in a constant direction, no matter how small its magni-
tude, will effectively transport the particle. On a topo-
graphic high, the net result would be a winnowing of the
detrital material of a size determined by the force which is
competent to put the particle in suspension. Thus, the sedi-

ment would be transported from a topographic high area to a

> sie an fast smug a ‘ea inne |

tena, raaakaneinty fo ade v tei. hp bt bach ‘eye
‘ mela Re srbianibnt ota sisi ne oommanial ae boa)

aes ristanihaine nai Mamiernta “mig tsod akbar) py a

ato} sme |
Coons ladges qm Seusiecan) ono? Pantleass ee sald ‘Ya

ae aot eve’ ‘ots aie teoumihaw ew eeTEI

Cp argu abd. Siseen “ye Awbam aR antenodhh pestis: bt

aan Bore:

ohhen att RR: notin a ads

pi tah

lower part of the sea floor by currents, turbulence, and
gravity. The settling velocities for very fine sand (0.1 mm)
at 20°C is 0.778 cm/sec. and for clay 0.000892 cm/sec. Since
the settling velocities for particles of these sizes are low,
they could be carried far before settling. The distance of
transport would depend on the height above the bottom and the
velocity of the transporting current.

Turbulent motion may be caused by waves or currents. In
Santa Monica Bay convection currents resulting from the distri-
bution of density are too small to produce any significant
turbulence near the bottom. Revelle and Shepard (1939) believe
that the chief transporting forces must be tidal and non-
permanent eddying “slope” currents resulting from wind action.
Although these currents produce no net transport of water,
they are rapid enough even at considerable depths to generate
pronounced turbulence. Turbulence thus produced tends to be
strongest over banks and other obstructions. It is likely
that such turbulence exists on the outer shelf in Santa Monica
Bay. Current measurements and the analyses of slope currents
at depths of 100 to 180 feet show that velocities of as much
as 0.2 knot may occur on occasion.

The only data known concerning threshold velocities is
the work by Hjulstrom (1939) and Inman (1949). The minimum
threshold velocity necessary to erode sediments already
deposited on the bottom finer than silt (1/16 mm) is about
35 cm/sec. (0.7 knot). It has been noted by several sedi-
mentologists that particle sizes of about 0.18 mm (fine sand)

require minimum threshold velocities, and that the threshold

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etoaes: at ” @itatod? joan teed vadto tutw eatenbe savy
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{ heres, snk?) We $1.0 sued, i ene eel
hlognersa digi dmett, bap, cedistogah

112

velocity increases for sediments both finer and coarser than
0.18 mm (Inman, 1949). It takes a current velocity between
0.5 cm/sec. (0.01 knot), and 20 cm/sec. (0.4 knot) to keep
sediment finer than silt in suspension, but if the velocity
falls below about 0.5 cm/sec. the material will be deposited.
Shepard (1948, p. 63) made 14 to 21-hour current measurements
in Santa Monica Bay with a tripod resting directly on the
bottom. Three current meters were superimposed on the tripod
at 21, 51, and 126 cm above the bottom. He found few measure-
ments over 10 cm/sec. and the maximum was 15.9 cm/sec., 84 cm
above the bottom, One series showed extreme variability and
the other series in the same general locality showed less
variability but equally low maxima. Bottom current measure=-
ments by the Hancock Foundation over most of the shelf
generally were between 0.1 and 0.4 knots. Consequently, if
Hjulstrom's values are correct, then fine sediments should

be deposited. Since the fine material is not continuously
deposited, some mechanism must operate to keep it in sus-
pension and carry it beyond the shelf. Inman (personal
communication) has theorized on the possibility of "beat™
effects resulting from the impinging of waves on the adjacent
shores aS a possible mechanism.

Shepard (1941) has discussed some of the possible
explanations of nondeposition on the sea floor off southern
California and covers the following possibilities: (1) effect
of waves, (2) tsunamis (tidal waves), (3) tidal currents,

(4) non=-tidal currents, and (5) mudflows or submarine land-

slides.

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~ mete ms ay ll ed) ‘ a-ha ba insatDen agora gta r

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hme bn wad ea) ‘wee, De ae haink.

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113

Effect of Waves

Vening Meinesz (in Kuenen, 1939) reports that submarines
are moved considerably by waves at depths of 60 m (200 ft.)
during rough weather and he showed how waves approaching
shelves have their energy concentrated near the break in
Slope. Kuenen, therefore, believes this accounts for the
common concentration of coarse sediments at the edge of many
continental shelves.

Dietz and Menard (1951b), in discussing the origin of
continental shelves and slopes, state that “effective erosion"
does not exceed 5 fathoms (30 feet). Buffington (1956) takes
exception to this view and gives information collected during
more than 5,000 dives by Geological Consultants of San Diego.
He says that when a diver moves from a depth of about 150 feet
to water 90 to 100 feet in depth, there is little or no evi-
dence of disturbance caused by currents or waves. The only
exception to this is around headlands and points where bottom
currents are occaSionally observed. At a depth of 70 to 80
feet there is frequently a noticeable bottom water movement.
or surge. This implies that bottom motion extends to a depth
of at least 80 feet and perhaps occasionally to more than
200 feet.

Long period waves or storm waves may generate sufficient
bottom motion to carry sediments off the shelf. These waves
arrive so rarely that they have not been observed in Santa
Monica Bay directly. However, bottom photographs taken off
Osborn Bank near Catalina Island show a series of large

partially destroyed ripple marks. These ripple marks were

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: Mawr ae atpak eh spate <AIGeh At 14eh OCR pag oe 4
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08 on i aye eM dahl nado » yitanubenaig 7

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at 9 Tae ae Mitsnotens: My eaaitaieg ba test os ieee

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ope kone migabe saad a ava

114

possibly formed by long southerly swell in the summer and
then reworked by bottom dwelling organisms (see photographs
of Emery, 1952, p. 68").

It is noteworthy that sediments are coarser along the
edges of the shelves in Santa Monica Bay as shown in Figure
20, It is possible, therefore, that waves (or tidal currents)
may concentrate their force along the edge of the shelf and
cause this distinct coarsening. However, it is improbable
that they result in nondeposition on the shelf, for the
area extends from the edge of the shelf near Santa Monica

Canyon far to the south and landward,

Possible Effect of Tsunamis

Shepard 1isregards tsunamis as a cause for nondeposition
off the southern California coast, Although one or two tsunamis
large enough to do any damage have reached the coast off Cali-
fornia in historic time, they are so rare and generally are
so reduced in force that they are probably not important in

causing nondepositional surfaces in this region.

Effects of Tidal Currents

Strong tidal currents form when large volumes of water
flow through a relatively small outlet. Velocities of tidal
currents may also increase at the break in the slope or over
any rise above the general level of the sea floor. Fleming
(1938) found a pronounced increase in the velocity of tidal
currents in the Gulf of Panama. Revelle and Shepard (1939),
on the other hand, found little evidence indicating tides to

be an important role in producing nondeposition off southern

° tit a0 bao Agisarse a ss

115

California. It must be noted, however, that no detailed
studied have been made on the effect of tidal currents in
relation to nondeposition off this part of the coast.

A few bottom current measurements were made up to 24
hours duration in various parts of Santa Monica Bay, but no
currents were ever recorded which could be directly related
to tidal action. It must be concluded, therefore, that tidal
currents cannot be the direct cause of the low sedimentation

rate on the outer shelf.

Non=tidal Currents

Non=-tidal currents include internal waves and large
moving eddies with vertical axes. Shepard (1941), utilizing
Hjulstrom's calculations, reports that in all of the localities
investigated off southern California, sufficient velocities
were found which would transport fine material, and in some
gravel could be rolled across the bottom. There were con-
siderable lapses in current velocities in some nondepositional
areas which would allow deposition of all sediments except
silt and clay. To put the material that had been deposited
back into suspension would take high threshold velocities,
but the measured velocities (36 cm/sec.) would take sand
(.05 - 2.0 mm) back into suspension. Thus, the measurements
by Shepard and his associates are sufficient to explain the
by=-passing of sediments over the nondepositional surfaces, if
Hjulstrom's data applies to the ocean. Shepard (1941, p. 1882-
83) questions the importance of these currents because (1) the
currents are much weaker than those which are observed in land

stream where deposition is gradually building up the stream

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‘pt ately od sane tee oa asitghaonaa re co

ae :

amt tis. wauanid anusri99: newt "9.2 |

‘aed ak _ esate ota He oh:

116

bed, and (2) there appears to be no relationship between the
observed current velocities and the type of bottom. For
example, the strongest current was found on the slope off
Palos Verdes Hills where the bottom is covered with mud.

Cores showed that mud was deposited to a considerable thick-
ness in several localities where currents were relatively
high. In addition, two water samples taken about 3 feet above
the bottom during the time of maximum observed currents failed
to show any traces of suspended sediment. In both cases, the

bottom was covered by silt and fine sand.

Mudflows and Submarine Landslides

Shepard (1941) points out the importance of submarine
Slides as a cause for nondeposition on some surfaces. While
these slides may be important in some localities, such as the
head of submarine canyons, the relatively horizontal surface
of the outer shelf in Santa Monica Bay probably cannot have
Significant slumping. Perhaps the exception to this is along
the northern boundary of the rock and gravel area where it
borders the southern part of Santa Monica Canyon. Parts of
this sediment cover may possibly slide periodically off into
Santa Monica Canyon. Sliding also takes place along the
basin slope, but the study made by Emery and Terry (1956)
along the Palos Verdes Slope indicates that considerable
thicknesses of sediment can accumulate before the sediment

becomes unstable and slides take place.

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“idevahhenos’ tats ait ob tesh its ns eataat bitch sit

117

Relation of Bottom Character to Surface Currents

Shepard and MacDonald (in Revelle and Shepard, 1939,
p. 278) report that during a period of calm weather near the
head of Santa Monica Canyon, they observed a surface current
set to the southeast during the flood tide, whereas there was
no appreciable current during the ebb. The same phenomenon
was observed during the present survey, but the currents were
always weak. Shepard and Revelle state that if the south-
east current also exists on the bottom it might carry material
to the canyon from the northwest, dumping its load in the
canyon so that the water would be relatively free of sediment
when it approached the shelf on the south. If such a net
current flow exists, there is no reason to believe that the
current would drop its load when it reached the canyon. Also,
the nondepositional surface extends a considerable distance
landward of the Santa Monica Canyon so that if such a current
were Carrying sediment, it would not cross a depression before
reaching the rock and gravel area. Furthermore, the net current
flow along the bottom varies through the entire east quadrant

and may at times have a seaward set.
Conclusions

The presence of rock outcrops, abundance of phosphorite
and gravel, the great number of borings made by pholads and
echinoids, and abundance of CaCoz are indicative of nondepo-
Sition. However, the presence of some fine-grained material
indicates that there is some deposition, although it may not

be permanently deposited. The origin of non or slight

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118

deposition surfaces is not yet clearly understood, but it is
known that in most cases it is due to by-passing of fine sedi-
ments by currents or turbulence,

If Hjulstrdm's calculations are approximately correct,
then the average velocity of the bottom currents on the outer
shelf is not sufficiently strong to cause erosion in the area
nor prevent the deposition of fine sediments. This does not
mean that strong currents or turbulent action do not, at times
occur. There are insufficient data to determine whether the
sediment by-passes the region of nondeposition or is deposited
and periodically removed by occasional strong turbulence and
current action. Since much greater velocities are required
to move sediment after it has been deposited than to transport
sediment in suspension, it might be reasonable to conclude
that the sediment by=-passes the area.

Turbulence resulting from internal waves and eddy currents
are possibly the cause in this case for nondeposition. However,
it is also possible that occasional storm waves, shore wave
reflection, and to a minor extent tidal currents may be impor-

tant.

SOURCE, TRANSPORTATION, AND DEPOSITION OF
SEDIMENTS IN SANTA MONICA BAY

Source of Sediments

The principal sedimentological studies undertaken during
the course of this survey have been descriptive in nature.
As a result, the discussion of sources of sediments is primarily

based on published and unpublished data.

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119

Much information on the general nature of the source
rocks can be determined from the mineralogy and organic con-=-
stituents of sediments. For example, the presence of Forami-
nifera of Miocene or Pliocene age in rocks of Recent age would
indicate that the contributing sources included rocks of the
older ages. Mineralogically, suites of heavy minerals,
including minerals typical of igneous and metamorphic rocks,
would indicate the relative importance of these sources.

For the purposes of tabulation of sediment contributions
and losses, a general budget has been noted in Table III.

Of the listed contributing items, it is possible to
indicate those of least importance. Gains from wind, chemical
precipitation, organic production, sewage and industrial wastes,
and artificial fill can be regarded as minor. Erosion of sub-
marine rock outcrops is also probably relatively unimportant
due to the restricted area of such outcrops in areas of active
erosion by waves, and currents. Wave erosion of sea cliffs is
not known, but papers by Revelle and Shepard (1939), Grant and
Shepard (1940), and Shepard and Grant (1947) would indicate that
this contribution is minor. It becomes evident that the major
contributing sources are littoral drift and stream-carried
sediments. The relative importance of drift versus stream trans-
port is not well-defined at present. The effect of Point Dume
as a sediment transport barrier to the north is controversial,
for example : [rask. (1952), Handin. (1951), Trask. (1955). At the
northern end of the bay the evidence leans tovard a southerly

movement of sand around the Point Dume area of unknown volume.

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120
' TABLE III

SEDIMENT BUDGET FOR SANTA MONICA BAY
(beaches and shelf )

Gained

Erosion of land within Santa Landward transport of beach
Monica Bay tributary sediment.
drainage areas; sediments
transported to the sea by Transport of fine sediment
streams and rain wash. beyond the shelf by
currents and waves.
Transport of sediment into the
bay by littoral currents from ||Periodic slumping or submarine
the west and north. landslides carrying sedi-
ments on the shelf, basin
Wind transported sediments. slope and in the submarine
canyons seaward into deeper
Erosion of sea cliffs. water.

Erosion of the sea floor.

Chemical precipitates from sea
water (phosphorite, etc.).

Organic debris (shells and shell
fragments).

Sewage, industrial, and shipping
wastes.

Artificial fill; artificial nouri-
shment of beaches, dumping of
sediments along the coast for
highway construction, etc.

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121

The movement of sand along the central bayshore has been
the subject of several investigations in past years. Asa
result of these studies, it seems probable that the bay acts
as a trap for most of the entering sedimentary material coarser
than fine silt and clay. Such a conclusion indicates a negli-
gible transport around Palos Verdes Hills coast. This is
likely true because of (1) the probability that most of the
sediments carried to the south by littoral currents are trapped
by the Redondo breakwater or are carried into Santa Monica-San
Pedro Basin through the canyon; (2) observations by the U. S.
Army, Corps of Engineers (1955) indicate that there is a pre-
dominant downcoast drift of sediment to Redondo, and a net up-
coast drift between Clifton and Rocky Point; (3) Johnson (1940)
noted that between 1939 and 1940,370,000 cubic yards of sediment
accumulated on the south side of the Redondo breakwater, but
very little on the north side. He postulated a southeast source
for the sand drift. It may also be, however, that conditions
are such that the sand is by-passed around the breakwater and
deposited on the southern side, thus originating from the north;
(4) bottom samples close to shore around the Palos Verdes coast
indicates rocky bottom and little or no sediment cover. Only
small pocket beaches of locally derived composition occur along
this rugged section of the coast. Most of the shore consists
of rock platforms and cobble beaches; (5) wave refraction dia-
grams in the southern part of Santa Monica Bay show that a
northward drift near Rocky Point would be accomplished with
greater ease than a southeast drift around the Palos Verdes

Hills; and (6) more or less permanent rip currents occur in the

rrr.
N om ri bat w cnabiorsete ts nana aa ates fer

cone

te a ataos ag Pe eE tS r eee cen sa ie os

0s en
Pe

is io spetaeweintnt Cee itil! aot Yo ht weer! ol 16) badn
tateatheamehte @ hint etis¥ ou,‘ wl)
i : im ee te 00 vou a

i de ait nae ebrioa yt. aed r (phibe kexed2tii, auth Bere

. eno2 edt aoded. Mba, Slecusie tay) ahi gt spel won phe
een? Oreo! Nicautition oat a ya lol mat hou een

“phos thiben Gok leer Bil: Sen iecrerty qibaoe t., te esdvend iatoog 1
ayehanoy avai” iat Lo bigeeat' 3 igs pets ve one Rene apes

ait obtonyiex min ise) peade ond asdios Beis = oe |

122

vicinity of Redondo and Clifton and indicate a convergence
of littoral currents in this area.

Therefore, the sediment within the bay probably represents
all sediment contributed by local stream drainage plus littoral
drift contributions from the north minus the loss of fine
grained sediments to the offshore area, and the loss of coarser
sediment down the submarine canyons to the basins. Some losses,
although very minor, also can be charged to wind drift from the

beaches inland.

Drainage Tributary to Santa Monica Bay

Figure 3 shows the boundaries of the drainage areas and
the streams bordering Santa Monica Bay. Table IV lists the
areas and characteristics of the various zones. It can be
seen that the Santa Monica Mountains comprise the major
element. The area southeast of Santa Monica Harbor is mainly
coastal plain, while that northwest of the harbor is primarily
mountainous.

Inland from Malibu several water supply dams have been
built which cut off much of the coarser sediment from the bay.
As this watershed alone constitutes 58% of the drainage in
this area, the remaining smaller watersheds have been lumped

together.

Rate of Sedimentation

It is difficult to calculate the rate of sedimentation
in Santa Monica Bay for several reasons. A number of the

problems concerned with source areas are obvious. The volumes

188 sobnowt amar oo

ne sere satan ot te eepreen suit avoda C fe
ie ae dhdat {ya8 sotqott esya? anbyobrad
se Mbp tT “anion apokier sar Ye ‘eobvetzets
feLan ont wake’ ahha tie: no kaon otaaé esd 4
| wae. ek godten soknem wife le teaadtooe neta om: |
baer ee esac! edt io teewmpoe tats ‘ore ema

aged ovad net yiguee stan ibseves wot Lats wor desta on
o¥ad ony aout Sramtboe Aegaeud off to some 3te ues rca |

123

TABLE IV

DRAINAGE AREAS OF THE SANTA MONICA BAY AREA

Total Area:

Area

Mountainous region (elevations to 2,500* )------= 217 ‘sds
Coastal plain region (below 500° )--------------- 120
Areas adjacent to coast without well

developed drainage -------2---9- 9 999 9 nn 10

TER SE I I IO 347 sq.
Southeast of Santa Monica Harbor:

Ballona Creek Watershed ---- -----92----- ---=------ US SGie
Kenter Canyon Watershed ---- ---9-- --9--29-9-9---= 10
Sand Dunes and northern Palos Verdes Hills------ 19
Total -9 en wn rn a en rr rr rrr err ee err senna 160 sq.
Northwest of Santa Monica Harbor:

Malibu Creek Watershed ----= ----=9-----9--------- 109 sq.
All other smaller watershedS---<--~-----------<--= 78
Total ---- 22 on on nn rn rrr rrr errr srr 187 sq.

mi.

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Bs rte ae atuat 9 + RSW

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A adi ialteaisaabcoiieet alah aha Pee Mee wm tr P . donee "4 AD De,

Rd hak be eg cy) A WR ate ee pela

124

of sediments calculated by various authors are based upon
conditions existing at the present time, but the volume has
varied greatly. Numerous natural and artificial changes in
the drainage areas have taken place within historic time which
have greatly altered the sedimentary regime of Santa Monica
Bay. The following is a partial list of some of the most
significant changes:

1. Construction of storm drains and debris basins
which have greatly altered the former natural drainage and
as a consequence, the amount of detritus reaching the bay.

2. Construction of the coast highway which has
prevented cliff erosion. On the other hand, large quantities
of sediment have been dumped along the coast in order to
widen the highway. Davidson (in Cong. Docs., 1897) reported
that in 1872 when traveling in a wagon along the northern
part of Santa Monica Bay, the cliffs came so close to the
shore and the canyons were so steep, that he could only pass
this region at low tide. As proof of former erosion of the
cliffs in this region, Davidson says:

"At Point Dume a very fierce westerly wind
Sprang up and retarded my operations so that
in returning to Santa Monica I was on the
beach through two low waters. I found the
beach torn away along the whole shore line,
and met with rocky obstructions which in

some cases had been wholly uncovered by the
washing away of the sands. As we approached
Santa Monica the evidences of this destructive
action became more and more marked, and for
the last 2 or 3 miles the beach was torn away
from 10 to 12 feet in depth.”

3. Urban development has stabilized erosion over
most of the coastal plain and parts of the Santa Monica Mountains.

4, Widening of beaches by artificial nourishment, con-
struction of breakwaters, and by the use of groins and jetties.
The construction of coastal engineering structures above Pt.
Dume has also cut off large amounts of sediments that may have
reached the bay in the past.

5. Beach erosion by the construction of breakwaters,
i.e., downcoast from Santa Monica and Redondo breakwaters.

6. Stream piracy of the westward flowing Los Angeles
River, and also the changes made in Ballona Creek outlet.

7. Construction of reservoirs which have greatly
reduced the quantity of sediments reaching the bay. At the
present time only very fine material is washed over the dams
and reach the sea. The following are the most important

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katate Tet ssn OF8 nana) eitt

125

reservoirs and the date of their construction; all are in the
Malibu Creek watershed: Rindge Reservoir (1925); Craggs Lake
(1913); Malibu Lake (1923); Lake Eleanor (1881); Lake Sherwood
(1904).

Other questions arising when calculating the rate of sedi-
mentation in Santa Monica Bay (specifically the shelf) are the
following: (1) How far are the sediments transported before
they are deposited? (2) Are the coarse sediments deposited
close to shore and most of the fine material carried great
distances, i.e., beyond the shelf, before being deposited?

(3) How much sediment is carried seaward along the floor of

the submarine canyons, especially Redondo Canyon? (4) How much
sediment is deposited along steep slopes or at the head of the
Canyons and later slumps into deeper water? (5) What volume

of sediments is winnowed from the shelf and carried beyond the
shelf before being redeposited? (6) What effect do animals

have on breaking down sediments thereby producing finer material
that may be winnowed away?

Theoretically there should be an even gradation from coarse
to fine sediments in a seaward direction. In general, this
theory applies to Santa Monica Bay although there are several
parts of the bay that appear anomalous. Some of the abnormal
regions are due to quiet water close to shore (Redondo Canyon)
which allows the accumulation of fine detritus. One of the
major causes of the peculiar sediment distribution undoubtedly
results from the superposition of present day sedimentation
on top of a surface formed largely in the geologic past. For
example, the rock and gravel area on the outer shelf is believed

to have formed in late Pleistocene or early Recent time. Thus,

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fanronds out ta sa02 Cr aia sins wade Aid ‘att Yo.

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i ‘ ew

126

a general seaward decrease in texture exists, but it is modified
by (1) the presence of sediments deposited in the geologic past,
and (2) submarine topography which in part causes deviations in
the sediment distribution.

Probably most of the clay and a large portion of the silt
originating within the distributary drainage area is carried
beyond the sheif and deposited in the offshore basins. It is
likely that bottom scavengers break up sediments into smaller
particles, but there are no quantitative data on this process.
It is probable, however, that beach sand does not become
appreciably broken down by transport along the coast by littoral
drifting (Mason, 1942).

Since littoral drift along most of the shore is southeast-
ward, and meets northward drifting sand at Redondo, some of the
sand must go seaward = presumably out through Redondo Canyon.
After the construction of Redondo breakwater, much of the south-
ward drifting sand was trapped by this structure. Prior to the
construction of the breakwater, however, a large amount of sand
may have been lost through the canyon. According to Mr. William
Herron, Army Corps of Engineers (oral communication), a con-=-
Siderable quantity of sand is lost seaward between Santa Monica
and Redondo, and at the present time it is possibly as much as
150,000 cubic yards per year.

Although sediments may accumulate on slopes and later slide
off into deep water, this does not seriously effect calculations
on the rate of sedimentation on the shelf. More important, how-
ever, is the amount of sediments deposited and later resuspended

and carried in a seaward direction. The more or less continuous

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127

redistribution of sediments makes it difficult to determine
how fast sediments accumulate at any*particular point. Sedi-
ment traps have been constructed by Emery and placed on the
sea floor off southern California. Apparently, most of the
sediment collected in the traps is the result of the movement
of sediment along the bottom. A number of investigations in
various parts of the world have shown that in relatively
Shallow water, where the investigations were made, there is
an almost continuous change in the texture of the sediments.
Thus, the median diameter, or per cent sand, silt, and clay
vary greatly over relatively short periods of time. It can
only be assumed that sediment movement along the bottom is
zero at any particular time when the calculated rate of sedi-
mentation is made; or in other words, the sediments are in a
"steady state condition”.

Assuming that 80% of the sediments are deposited within
8 miles of shore or over an area of 200 square miles, and the
estimated volume of sediments is 478,000 to 650,000, then the
rate of sedimentation would be between 0.02 and 0.03 inches
per year. Thus, even if the calculations are off by factors
of 2 or 3, the overall rate of sedimentation is slow at the
present time.

While it is not possible to quantitatively estimate the
rate of sedimentation over a long period of geologic time, a
few conclusions can be reached on the relative rate of sedi-
mentation and to changes in the depositional history of the

Day.

ner youre sang a ees wee jen ou

Ve Bobet Eiki evhiahen ste: ater betel “1 pei a! ;
seh heron 207 6a, | heaaiinedeek oath ct

128

Natural or artificial changes in the tributary drainage
areas and changes resulting from other works of man, are
indirect evidence that the sedimentation in Santa Monica Bay
has varied. In addition, it can easily be shown that pro-
nounced changes in sedimentation have taken place by exam-
nation of the sediments in the bay.

There are a large number of cores, jettings, and
borings taken in various parts of the bay and on land
close to shore. They show that numerous textural changes
occur in a short vertical section of any random core or
jetting. Thus, there are distinct beds or laminations of
gravel, silt, sand, clay, silt and gravel, beds of shells,
and even layers of vegetation. Although cores that are close
together may show some correlation, there is in general a
poor core to core correlation. The pronounced alterations
in texture can only be explained by changes in the competency
of the transporting agents(waves and currents), and to
variations in the supply of detritus supplied to the bay,
and/or to alternate cutting and filling of the nearshore
shelf sediment surface.

Rain falling in the tributary drainage areas can have
several different effects upon the supply of detritus to the
bay, depending upon the amount and distribution of the preci-
pitation. If the rainfall is small, only silt and clay will
be brought to the bay. If there is slightly more precipitation,
considerable amounts of coarser sediments, especially material
of about fine sand size may be washed to the bay. If a flash

flood occurs, material ranging in size from clay to boulders

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quel esaob aquodtia anita To gewad

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; “4a “bes Cetasaws bis Savon has eh Bek omer
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. YR Bl Lenslann thpadho'tt
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at nk ert eae Hey eae Hip ‘abontts sao
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tetistem a tabgeqes! “bbe Le a eto is
» Goa 4 tad out or taanow wea ibe |

129

may be carried to the sea. If there have been several years
of only small rains, the stream may have built up to a thick
deposit of sediment in its channel. Then when a flash flood
occurred the sediment in the channel may move out into the
bay as a plug of sediment (Revelle and Shepard, 1939). Under
such circumstances a great heterogeneous mass of unsorted
fragments will be deposited in the bay. Waves and currents
may then redistribute the sediment over a larger area.

The presence of considsrable quantities of coarse sedi-
ments, especially gravel, over a large part of the bay probably
indicates that sedimentation in the past was faster than now
and the source of sediments was much greater. The volume of
sediment brought to the bay during periodic storms must have
been great. Cores taken far out on the shelf generally do not
show many distinct beds of gravel, but gravel is widely distri-
buted over most of the bay as was shown in Hayward grab samples.
This distribution may be the result of extensive reworking by
marine processes after initial deposition.

Distinct and correlative beds of clay are conspicuous at
the site of the Santa Monica breakwater and farther to the
south. Clay can only be deposited in quiet waters which are
not disturbed appreciably by waves or currents which would
wash away the clay, nor can there be a large supply of coarse
detritus. The thick deposits of clay are therefore difficult
to explain unless it is assumed that one or more offshore bars
allowed fine grained sediments and vegetation to accumulate in
the quiet water behind the bars. These hypothetical offshore

bars migrating landward might have been the major source of

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ah eed Pye
CH he's
7 Poo,

130

sand in the El Segundo Sand Hills. Several geologists who
have studied the sand dunes have concluded that they might be
the result of offshore bar migration.

The above discussion is sufficient to indicate that con-
Siderable changes in the depositional history of the bay have
taken place, and that on the whole, the rate has decreased in
historic time. The changes are attributed largely to alterations
in the tributary drainage areas and to the work of man, but
climatic changes may in part be responsible for the decrease in

the rate of deposition.
Deposition in the Past Two Decades

A comparison of Shepard and MacDonald's samples with
those collected by the Hancock Foundation reveal that nearly
all of the samples collected in the 1934-38 period or earlier
were coarser-grained than those pp eared approximately 22
years later. There are several possible explanations for
this: (1) Shepard and MacDonald used a pipe dredge to collect
their samples and some of the finer sediments may have washed
out during the dredging operation. Dr. Shepard (personal
communication) reports that a piece of cloth was used over
one end of the dredge, and that once the dredge was full little
washing took place. (2) The mechanical analyses made by both
collectors were different. The samples collected by Shepard
and MacDonald and the Hancock Foundation used standard sedi-
mentary techniques. However, the Emery settling tube was
used to analyze the coarse sediments at Hancock Foundation,

whereas the earlier samples were analyzed using screens. The

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a

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131

settling tube technique is comparable with analyses made by
screens, so that no difference should have resulted in the
sedimentary parameters from these practices. (3) There has
been an increase in the percentage of fine sediments,
especially silt and clay, since Shepard and MacDonald collected
their samples. It is known that the volume of sediment
reaching the bay has decreased in historic time. It might be
reasonable to conclude that there has also been a decrease in
grain size. In other continental shelves and submarine
regions where sediments were collected again after a lapse
of time there frequently are pronounced changes in texture.
In some areas where sediments have been collected only a
month apart the various sediment parameters may differ
so greatly that there is little similarity to be seen.
Although an attempt was made to quantitatively measure
the rate of sedimentation by comparing Shepard and Mac-
Donald's samples with those collected by the Hancock
Foundation (Table V), the results were inconclusive because
it was difficult to accurately estimate the sediment thick-
ness represented by the samples. The only conclusion that
can be drawn from the two sets of samples is that most
of Santa Monica Shelf appears to be accumulating material

finer than prior to about 1934.

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teow tna leon ‘cen te ater owt aut moa |

132

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Other changes appear to have taken place since 1934-38
in the bottom sediment distribution. The most outstanding is
the lack of evidence of a rocky area reported by Shepard and
MacDonald to be one to two miles offshore between Playa del
Rey and Manhattan Beach. Shepard and MacDonald stated that
part of their data was based upon aenerts by fishermen and
also bottom notations by the U. S. Coast and Geodetic Survey.
It is possible that this region was delineated largely on the
basis of scattered notations of hard bottom that actually may
have been gravel, since it has been found that gravel is wide-
spread nearshore. At that time extensive patches of coarse
gravel perhaps were exposed at the surface and these were
taken to indicate rock. Nevertheless, there is no indication
of rock bottom in this region so far as could be determined
during the present survey, and either no rock exists here, or
it has been covered by a considerable thickness of sediment
since the earlier report was made. The submarine topography
gives no clue, for the micro-relief in this region is very

smooth.
Submarine Landslides and Slumping

While the vertical changes in lithology over most of the
shelf are explained by variations in the quantity and quality
of sediments deposited and also in part to oceanographic
conditions (waves, currents, etc.), the frequent textural
changes in cores taken in submarine canyons are due largely to

an additional factor - submarine landslides or slumping.

ree 0. asdo?ag ovtanodxe ekEt ‘tae: th

a o19W otodt fave ooat we per de DAROGLD ousw ae

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aie
train bse Ww spon bit Sides ashi xaos ayo beseves iad —

pakqmol? hay subitaoned smtramdue

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whi Earp tera bl i J ont at aro kee Lae “9 backetaxd wie
oltyexgenseag od fxs nit conte. ba) Detinogab: %

Eesutest raoupaat ONT 4 3x9 spinoymra ee

134

Sediments accumulating on a slope are unstable and the
stability of the deposit in general depends upon; (1) the size
and sorting of the sediment, (2) water content, (3) the degree
of compaction, and (4) the angle of the slope. Loose, fine-
grained sediment having a high water content and Aecunulatine
on a steep slope is unstable and eventually slides off the
slope into deeper water.

| Shepard has shown that slumping and submarine landslides
are common, especially when the canyons are close to shore
where there is an abundant supply of sediment. No quantitative
data exist on the periodicity of slumping, but it is likely
that the sediments are unstable on the slopes of submarine
canyons, and that slumping takes place fairly often. A
detailed study of a slope off Palos Verdes Hills indicated
that appreciable quantities of sediments may accumulate on a
slope before slumping takes place, but evidence was presented
that indicated slumping very probably did occur (Emery and
Terry, 1956). Benest (1899) pointed out the difficulties that
resulted from placing telephone cables across submarine canyons,
and the difficulty was not remedied until the cables were placed
on the shelf well above the head of the submarine canyons.

The cores taken in Santa Monica and Redondo canyons indi-
cate that slumping and sliding probably takes place, parti-

cularly in Santa Monica Canyon.

dace asbhllw (castes ehittwt ec 28! i
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W'S
GEOLOGICAL STRUCTURE OF SANTA MONICA BAY
Seismology

The seismological data used in the preparation of Figure
34 have been taken from the California Institute of Technology,
Seismological Laboratory, Bulletin on Local Shocks. The four
types of “Quality” shown in the legend of the diagram refer to
the accuracy in location of the epicenter. "“Magnitude™ ("M" on
the chart) refers to the relative movement of the ground using
Richter*s scale (Gutenberg and Richter, 1942). The magnitudes
range from O to about 83, the latter being the largest shocks
recorded anywhere in the world. A brief comparison of magni-

tudes and their approximate extent in damage are listed below.

Magnitude Effects

0 Slight shock = probably imperceptible to humans.

1 Slight shock = possibly felt near epicenter.

2 Very small shock = felt slightly over a small
area of a few miles in radius,

3 Small shock = felt sharply over a small area,
but incapable of causing any but insignificant
damage.

4 Moderate shock = may cause considerable minor

damage near the epicenter; felt to a distance
of about 45 miles.

5 Minor shock = may be destructive near the epi-
center, with damage over a larger area; felt to
a distance of about 125 miles.

6 Major shock - a strong destructive earthquake.

7&8 Progressively stronger destructive earthquakes.

The Long Beach earthquake of March 10, 1933, had a magni-
tude of about 6.3. The last series of major earthquakes in
southern California of comparable magnitude were the Kern County
shocks of July and August 1952, which had magnitudes of 7.6 to

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136

Figure 34, Distribution of epicenters in Santa Monica Bay.

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All shocks, including aftershocks, from 1934 to April 1955,
are shown in Figure 34. The shocks are located to the nearest
minute of latitude and longitude, and the qualities on the chart
are shown by the varying style of lettering for the magnitude
number.

It is difficult to make definite conclusions about the
relationship of earthquakes to the geological structure of
Santa Monica Bay for several reasons; (1) most of the shocks
are poorly located (2) statistical studies of the earthquakes
are not possible due to the inaccuracies in location, and (3) in
most cases, earthquakes do not originate at the surface, but
at a depth of several miles.

Most earthquakes in the California region are associated
with faulting. Numerous large faults and countless small faults
exist in the vicinity of Santa Monica Bay. The largest and
most important fault in the region is the Newport-Inglewood
fault zone, which originates in the Santa Monica Mountains
near Beverly Hills and continues more or less uninterrupted to
Huntington Beach where it goes out to sea. The faulting in
this zone is not one major fault, but is composed of numerous
short overlapping faults. Other fractures that may be of
importance to the geological history of Santa Monica Bay are
the Malibu fault and the San Pedro or Palos Verdes fault zone.
All of these have been discussed to some extent earlier in
this report.

The Palos Verdes fault zone is known to leave the coast
in the vicinity of Redondo Beach, but just what happens to the

fault after it reaches the bay is somewhat obscure. Some

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138

geologists think that the fault turns west or southwestward

down the axis of Redondo Canyon. However, there seems to be
more evidence that it may continue in a northwestward direction.
The following information perhaps supports this theory: (1) num-
erous 0il and gas seeps are found at the head of Redondo Canyon
and farther to the northwest, (2) the large grouping of earth-
quake epicenters in the vicinity of Santa Monica Canyon (lat.
B2057" 5 lone) 1189388"), C30the general pattern of the submarine
topography suggests that faulting perhaps has played a role in
its origin, and (4) the discovery of schist on the outer shelf
appears to correlate with the schist in Palos Verdes Hills and
the basement rock in the Los Angeles Basin.

Clements and Emery (1946) plotted epicenters for the off-
shore area in southern California and found them to be grouped
along straight steep slopes which they believed to be of fault
origin. No such groupings occur in Santa Monica Bay so that
the relatively steep slopes are probably due to other factors,
or the faulting that may have been important in the formation
of the slopes is now inactive. It is noted that Redondo
Canyon has the appearance of fault control since it is deep,
has steep walls, and has a straight longitudinal profile.
However, if faulting played an important part in its formation,
it must have been in the geological past since there is no
seismological evidence of faulting at the present time.

The only earthquake in Santa Monica Bay that has received
special study occurred on August 30, 1930 (Gutenberg, Richter,

and Wood, 1932) and was located in the area where a large

139

number of shocks are reported in the northern part of the bay.”
For more than three years prior to this shock there were numerous
small quakes which were felt in the beach cities. The main

shock had a magnitude of 5 followed by 16 immediate aftershocks.
Ioseismal lines (lines of equal magnitude) indicate that the
shock was felt more than a hundred miles away. It was calculated
that the shock originated at a depth of 6 to 9 miles below the

earth's crust in bedrock, probably granite.
Thickness of Overburden

Thicknesses of unconsolidated sediment in several parts
of the bay are shown in Figure 35. Thicknesses of less than
10 feet are found in the rock and gravel area on the outer
shelf, off the Malibu and Palos Verdes coast. U. S. Coast and
Geodetic Survey charts and a chart prepared by Johnson (1940)
also show rock off the coast of Malibu. The overburden increases
eastward from the outer shelf, and reaches a thickness of 500
feet within one mile of the rock and gravel area.

The scattered patches shown in Figure 36 are geophysical
anomalies and probably are due to irratic or scattered patches
of gravel, except some of the nearshore ones which may be rock

a short distance below the surface.

*This shock has not been shown on Figure 34 because it took
Place before 1934. Prior to 1934, earthquakes were not system-
atically recorded. They were largely “eye-witness™ accounts
and have little scientific value.

Rh 8%
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‘Pel. ees

140

Figure 35. Probable thickness of overburden in Santa

Monica Bay.

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k

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1830’ 25°
AF ra T T 7

Isa NTA MONICA BAY

° ' 2 3

STATUTE MILES
BOTTOM CONTOURS IN FEET

PROBABLE THICKNESS OF OVERBURDEN
(PLEISTOCENE AND RECENT)

LESS THAN 10 FT

EL SEGUNDO

MANHATTAN BEACH

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141

Figure 36. Areas of anamolous seismic data in Santa

Monica Bay.

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SANTA MONICA BAY

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STATUTE MILES
BOTTOM CONTOURS IN FEET

AREAS OF ANOMALOUS SEISMIC DATA

BO SS

———— —
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AREA OF ANOMALOUS SEISMIC
DATA, MAY INDICATE GRAVEL
BURIED BY FINER SEDIMENTS

EL SEGUNDO

MANHATTAN BEACH

HERMOSA BEACH

REDONDO BEACH

PALOS VERDES HILLS

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142
Structure

Figure 37 is a generalized diagram showing the lithology
of the upper few hundred feet of sediments near the shore. The
impervious clay cap in the upper part of the San Pedro formation
is believed by ground water geologists to extend only to the
shore in the region shown by the diagram. However, a similar
clay cap was found at the site of the Santa Monica breakwater
and also along the old Hyperion outfall course. In the
latter case, however, the clay in the cores may or may not be
the same clay cap identified on land, but at the Santa Monica
breakwater the clay cap was found in every core, at or very
close to the surface of the sea floor. The “Silverado zone"
of the San Pedro formation probably extends only 2 to 3 miles
offshore, but the other formations lower in the geologic
section may extend far out onto the shelf.

Two geologic formations in the Los Angeles region may be
correlative with the schist cropping out on the shelf; the
Catalina schist and the San Onofre breccia. The San Onofre
breccia is Middle Miocene in age; the Catalina schist may be
pre-Cambrian or Mesozoic (Jurrasic ?). The Catalina schist
underlies almost all of the Los Angeles region and crops out
in the Palos Verdes Hills. The San Onofre breccia was formed
by the erosion of the underlying Catalina schist, and consists
of angular blocks up to 10 feet in diameter (Woodford, et al.,
1954, p. 71). Even though there is a significant difference
in the age between the Catalina schist and the San Onofre
breccia, it is difficult to assign a definite age to the

schist fragments found in Santa Monica Bay.

rate

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143

Figure 37. Geologic cross-sections in the Santa Monica

Bay area.

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144

Perhaps only a small number of schist fragments have been
found in the region because the original outcrop had been
covered by Miocene and later sedimentary deposits and only
recently was partially uncovered by erosion. Since Pliocene
age Foraminifera have been found both to the east and west of
the rock areas and only Foraminifera of the Miocene and Recent
periods in the rocky area, perhaps erosion in post=-Miocene time
carried sediments from the topographically higher rocky area
leaving only Miocene and Recent age rocks where rock is now
exposed. If this is true, then the rock and gravel area has
suffered deep erosion, including deposits of the Miocene, the
Pliocene, and perhaps Quaternary periods. If deep denudation
took place in this part of the bay, the gravel might be a
residual deposit brought about by erosion and winnowing of
fine material. This process is similar to the accumulation
of "lag gravels” in desert regions in which the wind removes
fine-material and leaves a residual deposit of coarse gravel.

In the El Segundo oil field, the Franciscan (?) or Catalina
schist is overlain by a schist conglomerate and nodular shale
at a depth of 7,000 feet below sea level. The conglomerate in
this oil field was formed by the weathering of the underlying
Catalina schist. It is conceivable, therefore, that the schist
fragments and the gravel on the outer shelf have a similar
origin. A possible argument against this theory is the almost
complete lack of schist fragments or gravel composed of schist
elsewhere in the region, In addition, the gravel is not
restricted to the rock and gravel region on the outer shelf,

but is found in scattered patches over the entire bay.

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145

The schist cropping out on the sea floor may correlate
with the Catalina schist assuming that the equivalent to the
San Onofre breccia never was deposited on top of the Catalina
schist in this area or that the schist breccia (or conglomerate)
has been almost completely removed by erosion. Since the
schist outcrop on the sea floor is a topographic high now, and
probably was a high area when it was buried during Miocene
time, it may be reasonable to assume that no significant
quantities of fragments of schist could accumulate. Fragments
of schist that might have broken off during weathering prior
to burial would have accumulated in low areas, but a few
fragments of schist might have been incorporated into the
overlying shale.

Although the difference in geologic time between the
Catalina schist and the San Onofre is very great, sedimentary
rocks of Miocene and more recent ages frequently rest directly
on the basement rock. Therefore, whether the schist dredged
from the outer shelf is basement rock or its weathering product
is not too important.

Rocks in the El Segundo oil field located approximately
one mile east of Hyperion range in age from Recent to Jurassic (7).
Pliocene and post=Pliocene age rocks having an aggregate thick=-
ness of 5,700 feet are composed largely of alternating sands
and shales, except the lower 450 feet which is composed of shales
alone. Sediments of Pliocene age are underlain conformably by
1,300 to 2,000 feet of Miocene shales. The basal section of the
Miocene is made up of a nodular shale, and a schist conglomerate.

The Catalina or Franciscan (?) schist of Jurassic (7) age

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146

unconformably wnderlies Miocene age sediments. The stratigraphic
section is shown diagramatically in Figure 37 in which two possible
interpretations of the structure between the El Segundo oil field
and the outer shelf are presented.

The fossiliferous shales and mudstones dredged from the rock
and gravel area on the outer shelf are Upper Miocene in age and
correlate with the shales in the El Segundo oil field. The schist
recovered on the outer shelf is, therefore, correlative with
either the schist conglomerate or with the basement schist. The
structure between the outer shelf and-the shore can be explained
by one of two theoretical structures or perhaps by a combination
of them. They ares: (1) A very gentle dipping syncline or trough
exists with rocks of Upper Miocene age and possibly the schist
basement exposed on the western limb of the syncline, and Plio-
cene age rocks in the central part of the bay are covered by
sediments of the Quaternary age. Sediments derived from this
island and from land to the east eventually filled the trough.
(2) The Palos Verdes fawit zone extends northwestward from the
Palos Verdes Hills and has uplifted the outer shelf several
thousand feet. Rocks younger than Miocene have subsequently
been eroded away leaving only Miocene and perhaps basement rocks
on the outer shelf. The Palos Verdes fault dips steeply to the
northeast along the north side of the hills, but it would have
to have a relatively low dip to account for the changes in the
thicknesses in overburden on the shelf. It is noteworthy that
Corey (1954) and Woodford, et al. (1954) show a continuation of

the Palos Verdes fault across the Santa Monica shelf,

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147

It would appear, therefore, that on the basis of available
data there is a considerable thickness of sediment between the
coast which probably becomes thinner towards the outer shelf
as shown in Figure 38, Although sedimentary rocks of various
ages may be covered by only a thin veneer of Recent sediments
in the inner shelf region, it is highly improbably that basement
occurs at or near the surface anywhere in this area. A detailed
study of fathograms taken over most of the shelf indicated that
most of the inner shelf out to a depth of about 170 to 180 feet
is a depositional plain. This suggests that deposition of sedi-
ments has covered a large portion of rock of Pleistocene age
and older which possibly at one time were exposed at the surface.
However, some areas, such as the regions where red sand occurs,
and at the head of Santa Monica Canyon, relic sediments have not
been covered. Since some of these relic sediments do not have
any discernable relief, they must be at equilibrium with the
present depositional surface, and as sediments are spread evenly
over the entire region they will be covered. This assumes, of
course, that most of the shelf is undergoing aggradation, and
there appears reason to believe that this may be partly true.

No definite statements can be made for most of the other
parts of the bay since data are lacking. Nothing is known
concerning the age of the rocks beyond the shelf break, but a
large variety of rocks have been dredged from the submarine
canyons by Emery and Shepard (1945). A few of the rocks had a
possible age of Pliocene, but it appears as if the bulk of the
rocks should be dated as Miocene. No schist has been found in

the canyons. This imposes a very interesting question: If the

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148

Figure 38. Hypothetical cross-section across Santa

Monica Bay Shelf.

V3aY¥vV T3SAVYHY9D F WOON

149

schist on the outer shelf is basement or near basement (San
Onofre), then all rocks below the schist must be basement also};
which means that all rocks found in the deeper parts of the bay
should be composed of schist or at least basement rock of some
kind. Thus, if schist occurs on the outer shelf at the surface,
then only schist or basement rock should be found in the Santa
Monica Canyon. This is not the case since most of the rocks
dredged from the Santa Monica Canyon were Miocene in age. One
way to explain this anomalous problem is by assuming that an
east-west trending fault separates the rock and gravel area on
the outer shelf from the region north of the submarine canyon.
Such a fault would tilt the region north of the axis of the
submarine canyon downward, and uplift the outer shelf. In this
manner, Miocene and post=Pliocene rocks could still be present
in the canyon, but have been largely removed by erosion on the
outer shelf. Another alternative is to assume that the schist
dredged from the outer shelf is not in place. Third, the schist
and gravel area of the outer shelf may represent an eroded dome-
like structure.

Poland, et al. (1948) mentions that the Ballona escarpment
along the southern boundary of the Ballona Creek has character-
istics which suggest faulting. For example, the escarpment is
more or less straight over most of its length, but more impor-
tant is the fact that the gravels in the old stream channel are
thicker on the south side. The thickening to the south can be
explained by tilting of the land area to the south and by
assuming an east-west trending fault at the southern boundary

of the stream channel. It is possible that the faulting and

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150

tilting proposed by Poland, et al. also is responsible for the
tilting of the northern flank of Santa Monica Canyon.

A large percentage of submarine canyons have streams or
former streams entering into the head of the canyon. No
problem is involved in the origin of Santa Monica Canyon since
Ballona Creek is known to have flowed into the bay until 1825,
and probably flowed directly into the head of Santa Monica
Canyon when sea level was lower. Redondo Canyon, on the other
hand, has no historic, topographic, nor sedimentary record of
a former stream landward of the canyon. The only evidence
known which indicates that the region at the head of Redondo
Canyon may have had a stream is the existence of marsh or
lagoonal deposits at about sea level one-half mile inland.

Although faulting may have played some role in the control
of Redondo Canyon, some additional agent is necessary to cut
the gorge. Two theories which are most commonly argued for
the origin of submarine canyons are; (1) subaerial erosion by
streams, and (2) erosion by turbidity currents. A detailed
discussion of these theories and others are unnecessary here3
however, it is necessary to briefly state the turbidity current
hypothesis. Sediments accumulating on the shelf or in the
upper reaches of the submarine canyon periodically slump or
Slide into deeper water. The material that slumps has a very
high water content and travels at a high velocity which is
assumed to have the power to erode the bottom and walls of the
canyons.

It is obvious that there is no apparent abundant source of

sediments which could form turbidity currents; therefore, both

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151

theories appear to be inadequate to explain the origin of
Redondo Canyon. Two possibilities are proposed for the origin
of this canyons: (1) The two large tributaries on the north

wall of the canyon are the result of erosion by one or more
tributaries flowing from Ballona Creek. Thus, Ballona Creek
was responsible for erosion of Redondo Canyon as well as Santa
Monica Canyon. Perhaps the stream actually flowed out the head
of the canyon, but this is difficult to prove. Redondo Canyon
then could migrate landward by headward erosion. (2) A stream
flowed to the north of Palos Verdes Hillis, but is so old that
all evidence of its existence has been obliterated by later
reworking and deposition of sediments. The region might have
been a wide flood plain close to sea level and therefore could
supply large quantities of sediments for turbidity currents -
if this was the origin of the canyon.

A tongue of sediments extending from the western tributary
on the north side of Redondo Canyon towards Ballona Creek is
evident on most of the bottom sediment charts. This suggests
that the former stream channel may still be evident as shown
by the superficial sediment deposit, or present oceanographic
conditions have an influence on the distribution of sediments,

and for some reason are related to the old tributary.

“beset ae tuo bewolt {touton maeshe eit eae
:* - sited obmobos se7oxg oF ‘Hiab ee nova 2
Bi ee - megtse A (8) .nobeo=s veswhand yd Dsenb0r! orange bf bs _ bie
Gast bio os et tue .atttt dbus aeiet \o. tren sith
eesat vd betatetiide mood) wad waaste? co a3 te -.
vad ttghe nokot ud? -atabekbee to, voctiznges toe gokdgons4
_ Blso> sxoteaeds tina Tavel ave oF waste us aty teott 25k. a nosd o
ie ~ escormo qribidx? xo} atnsaibee te soisttoaup ops saa |
an vs snoqnes ett Yo nigise sit anti iat ®

: abst toes sins tata: semaine Yo Sell -
WW lak SesxD stobTnd ehsawak spyned phnodes to pote nibzen sa
edecgave 2beT ae
puote sa dnote st GLEE Yai Teansce menate poe
nbdqeigentsoe sagesan Yo \Fkeoqeb tnembhee Lstabideaee ath
jerneukoee 36 adiivdEenahd Sit? vo soneat ink wa sval Hoke
. eaistudien tite edt ot betaiog Daa Boeset emor 207 8

ize

152

SUMMARY

The Geologic and Geographic Setting of
Santa Monica Bay

Santa Monica Bay is bordered on the north by a mountain
range that has been uplifted along east-west trending faults.
On the southwest, the Palos Verdes Hills have been elevated
during relatively recent time. The north side of the hills
is separated from the Los Angeles Basin by a fault trending
in a northwest direction. This fault probably extends into
Santa Monica Bay and has played an important role in its
structural history. The relief in the Los Angeles Basin was
formed largely in Late Pleistocene and early Recent geologic
time and the tectonic forces responsibie for deformation
probably have also affected the submarine geology of the bay.
Thus, the structure of Santa Monica Bay is more related to
forces active in the Los Angeles Basin and Palos Verdes Hills
than to tectonic activity in the Santa Monica Mountains. Earth-
quakes on land and in the bay, and other lines of evidence indi-
cate that deformation is still taking place.

The major drainage into the bay is from the southern
slopes of the Santa Monica Mountains, while there is little or
no drainage from the area south of the city of Santa Monica.
Prior to 1825 Ballona Creek drained a large inland area, but
since that date only a minor amount of material has entered
the bay through the Ballona Creek outlet. A variable amount
of sand comes into the bay around Point Dume, but probably no

material finer than beach sand comes from this source.

| ietaven ry 1 ve iy08 ait ao Piyreod ad at watack shana? - : .
oe gaitmeat teserteag guoky coi qu’ heed sad sah osu |
ie baravels aned ovat ernst mabe’ sa bal seht temuttuoe say
a etka ort te ebée st3a@ tr «MES hese ylovetaten | a ius
| gaibasat tigal s yd meet antioycn ost aah mo'xd bedaragee i
| Ofat ehasixe | idaduxg +tea’ oh rth : hnsaah *emultron a
noe i 7 eth: me! Bfo2 inet xq ie bay ats eel: Rosh ad psknolt a
‘ a naw akend aofoyah el ody nm doi Loa Sey riotabd tatan me
y : . “plystony teeo88 qines hig satis. occ Cl stad ab qisgaad’t
ae thes nodtanw2eb 10? shdtemoqe:: cassel skeen 09s aut tan: snct
F ved out te THOLOeD pritemdvs oct) bstostis vain oved yid sow
- ; ot botetox Broo at wea aoliow slam ¥ Port ours sat eae
he eres sabrs¥ mole? hos nieul, enlageh aod sdf at aviton, pee

ie?

Pat “9x08 , tis En rw ‘eokaoM wion? of? Bh Yo lritos obnotaes, ors

a ;

a, yy
r oh

~<kbat SaseDaye Ro Senki wsdio Sno ved edt et Bae brad ne
pesatg gaktet tfive ub ne ktawro%eb tats

rmituos od mot Bk Yad wo otek oyptiband vol am ont

30 “Orton ek sxodd stn qantet nrokt bokinoy atned odd Qo. ; ;
»sakwon stnae 4g tks eit Yo Advoa sexs sie most vanntinba

ted ,nere bustit epnel & bor eth #e@tD sen bled ema ‘at

”)

bsastas esd Tatostam Yo tuow xockm a ine sted saat:
$mypome eidebiay hight uookD aid Eth) ot Agno ve
on videdorq tad , cmt omkes Baeots cai ‘eas nie nae

153
Submarine Topography

The major submarine topographic features in Santa Monica
Bay are the shelf, Redondo and Santa Monica Canyons, the Basin
Slope, and Santa Monica Basin.

The shelf is generally smooth and grades gently from shore
to a depth of approximately 270 feet. The surface shows several
distinct types of minor “micro-relief", Nearshore there are
bars and troughs, farther offshore are areas of smooth topo-
graphy with no micro-relief, and near its edges the shelf shows
variable micro-relief with small terraces and notches locally
present. On the portion of the shelf projecting between the
two submarine canyons irregular micro-relief consists of low
mounds and ridges and corresponds to the major rock and gravel
area.

The two submarine canyons are incised into the shelf and
create the lobate outer projection of the shelf. These canyons
are V-shaped with relatively steep walls. Redondo Canyon is
cut through the shelf to within a few hundred feet of shore,
whereas Santa Monica Canyon has its head about 353 miles from
shore.

At the edge of the sheif the gradient increases markedly
and the slope grades into an offshore basin. These slopes
appear to be smooth, but a few notches or terraces are Known
to occur.

The floor of Santa Monica Basin, starting at a depth of
approximately 2,700 feet is relatively smooth, but slopes

slightly in a seaward direction.

abhnow stone ak tien : : a woo: o-
(nboatt oat ssnoyen® sohno a

en oa ies aobaay 4 sa streor: otkesebee Pt sede: oot
o “anovee twore: oon tame. et. SOY} x ot mokneroge, te. ttqeb a ot
oP: wiz exedd eronerasit “Sart sn i ho, amet, sie |
_ ~aqot etooue Yo 6se38 tig wOdn? to todd a0 8 cede Te ban.
oe “ awodte | Made oat sents othiongag, bis ativa~orobn om, ante va
: q YELnsol aedotop tow emggrEst Line mtiw teator-exokns
_ ode ngswtod grid toolesq tlede adh i ok MG we ae
o ; a (Wet) te etakemno Tokiseeoroke 32 icj@eak aayinne
| Eau a to uae ody A oo kc bak. vin ai

bas Mode edt otnk beciont 920 anoymas eiiahiiue ont oot vill i
i enoynan geet? (4 tlety old to. cotdoghigag: 2hawo ow adek: out a
ee! aoyaas) obRo bo ~Rifew goatee, Yoavitelss dete Seats
. go rods. Be. Poet haved woe aidtiw of Lledas on? davords, aM |
Hert atta Pe trode teed 2th, awd soynet) aokio staat, al ety

eibetean asasetanl taokbany ont Yiede a4¥ Yo aubs. oad! a
asqole svedt ~sheM diomaT io oF ‘oth SPRatHy mao.te's
mond ‘ase aoe etime wiibyor wed @, tnd sires Weer :

154
Unconsolidated Bottom Materials

Sediments are classified on the basis of a three-component
system of gravel, sand, and silt content, and are subdivided
further on the basis of color. Although the sediments represent
a gradual progression from sand nearshore to silts offshore,
this progressive change is disrupted by areas of coarse sedi-
ment. These coarse deposits are composed of relic sediments,
organic debris, and authigenic minerals.

The highest percentages of sand are in the nearshore
regions, at the head of Santa Monica Canyon, and in some iso-
lated patches on the outer portions of the shelf. Sand is the
main sediment component in the bay. The greatest percentages
of silt are along the basin slope and in the submarine canyons.
Clay rarely exceeds 20 per cent of the sediment except in parts
of the submarine canyons and in the Santa Monica Basin.

All deposits have fine-grained sediment associated with
them, indicating that fine material is deposited to some extent
in ail parts of the bay. Intermittent removal of fine-grained
sediment may be the most important factor in preserving the relic
deposits.

An examination of the sand fractions of the sediment
resulted in the establishment of six distinct types; (1) fine
quartz-feldspar sand, (2) rock fragment sand, (3) glauconite
sand, (4) phosphorite-glauconite-shell sand, (5) shell sand,
and (6) red sand.

Fine quartz-feldspar sand covers most of the shelf, and is

the terriginous detrital material being deposited in the bay at

the present time.

“ade tt mee
pop ktavoxed deetiors oy 8 nl tarenegse 2 tae |
anaes: aii ramdud SAF GE) he beg Ee wipes at hone ome}
era a eid daoni bee wats i tooo ong OE etn eine

aay “nealexganit te davoust toute wie eet
i oiisy edt galvseeing nt aor ert Fite wo ye seo any ad am 9

Hramlbgs sot do tot shat, lye ‘eat te aot raainase

okt CL). Vesaed ir: “ike td vaendabteates . is

BUS)5)

Rock fragment sand is the coarse fraction of nearshore
and offshore sands and silty sands, and represents a relic
sediment that was deposited during lower stands of sea level.

Glauconite sand is the coarse component on the basin slope
circling ‘he outer shelf, on the seaward portion of the shelf
off the Malibu coast, and near the tip of the shelf south of
Redondo Canyon.

Phosphorite=-glauconite-shell sand is the coarse fraction
of the sands and gravels, and of the finer sediments of the
outer shelf projection between the two submarine canyons.

Shell sand occurs as the coarse component of some of the
fine-grained sediments on the basin slopes.

Red sand is in scattered areas in the nearshore region.
This material is a relic beach or dune deposit formed at
lower stands of the sea, and has not yet been covered by Recent
deposition.

The distribution of median diameters indicates that the
grain size of the sediments decreases in an offshore direction.
The decrease is modified by coarse relic material, authigenic
minerals, and organic fragments occurring offshore. Also,
slumping or sliding of sediment on the slopes tends to modify
this distribution pattern.

The distribution of coarse sediments in patches through-
out the bay tends to indicate that there are localized areas
of non-deposition, or areas of intermittent deposition.

The distribution of median diameters indicates that there
is continuous marine deposition taking place nearshore between

Santa Monica and Redondo Beach, and on the shelf off the Malibu

juoitoos th waotevie ma me seeaorsnd atromkbey ad} to oske we
lmbseghitoue )lekxed aor ok tern, gergoo vd bot ha bam: ek eaco798b. outt
eth verona lta: yabrineco atnomges? obragro bana +2 lars0a
vtkbow of abaot aeqake: a mo tosmi hee te wade te ne: miei

| | iy) .Srottag nobtedhat abt e
_méuabait nerdotog oh eiitakbes sRthoo ko. nodtndhetekb oat

anaes bortisoat O28 Oaerh Pas staat k ot ahmed ved

Mortisoqsh ner ELorce tech to node. #0 vaoks 2nd

wxeat Tate aerank bak eadtoeat naibom® to. 02d

156

coast. The sediments in these regions are affected by currents
and waves at the present time, and as a consequence reflect
present environmental conditions.

Most of the shelf sediments are well-sorted. Moderately-
and poorly-sorted sediments on the basin slope and on the
shelf occur in areas where relic sediments are found, and/or
where authigenic minerals and large accumulations of shell
fragments form part of the deposit.

There is a tendency for the shelf sediments to show better
sorting near the edge of the shelf, perhaps as a result of
stronger currents or turbulence which tend to produce better
sorting in the sediments.

With the exclusion of the area where the head of Redondo
Canyon comes close to shore, the sediment pattern is essentially
the same from shore to an offshore distance of four miles.

This pattern consists of an offshore gradation from sand to
sandy silt. The areas where relic sand is still exposed are
probably areas where sediment by-passing takes place. Also,
the shelf sediments are probably reworked occasionally and the
finer fragments are removed during intermittent erosion and
deposition.

At the head of Santa Monica Canyon, and inshore from the
central shelf projection 4 to 6 miles from shore, there are
sediments which are generally coarser than those nearer the
coast. The existence of relic sediments near the surface
indicates that sedimentation must be slow at present. This
may be due to either a smaller supply on this section of the

shelf, or to greater turbulence which prevents permanent

wutotarebel Sbetsone tian ip thsonione — ms v0 see

(gliabineere eh maaitaq tmeakhes: oft ~hrode ot aeots kemo2 doce
seakle wo? No ‘sostatedh wrodatio ice of sxede mont omae, sit
ot bxae next mohiabers waedetto ap to sthianes nxoting: whet |
‘gua Deaoqwe Litre ef baie pkbex Siakw eaaxe sat meres haa |
,ozlA oepmtd) eeches qitk aping-wect! Pant bow wxent BRO7R) vidationg |

odd bus yl ieagtessoe badbiow wes yifeis 2; 6 1 etnemt ten tied add §
bis ooltor9 Faatthayeral, gehen osvemes xe eteeapen? 1
te | nna eget

sit mox? siedeak bea gkeynad co eT: to) be ot) ‘OnE: 4
e210 oxo? svete meee eerie 3 Arb to bt osLoxq Viwda tas
edt FOG StOKT MEAT BHOtood PALATES’ OER | tod ste: et
eon tas 32) seem siaemibes Oo: em te oones edie wit,
Meet y Payeewe: te WLS ee Power ioetheaoebhes! tadt :
att 1s nokpoet eked do yhiyon aot amem sate a
Pe ite | adhe erg sedate aon stedaed 1 wataeta/ ed,

WENT

ore

accumulation of finer material. Fine sediment may (be deposited
in this area, but is removed or reworked more of ten than in the
areas close to shore. \

The central shelf projection contains an area of rock and
gravel, and the sediment distribution is patchy over tthe entire
area. Topographic evidence indicates mounds and depressions.
Sediments here contain authigenic mineral grains and she11
fragments which are often considered to indicate an ene
ment of non-deposition, yet the sediment containing these
components is often fine grained with appreciably amounts of
silt and clay. It is, therefore, an inescapable conclusion
that a large portion of this area is receiving sediment. In
all probability, deposits are accumulating in depressions on
this surface, and the small prominences which are the loci of
formation of authigenic minerals and of shelled animals are
being swept free of sediment. Most of the gravel area is
probably covered by fine-grained material, and gravel at the
surface is limited to the vicinity of the rock outcrops.

The percentage of calcium carbonate increases in an off-
shore direction. It is generally low over most of the shelf
and slightly higher on the offshore slopes. The exceptions to
this distribution are the high percentages found in patches
on the central shelf between Santa Monica and Redondo Canyons.
Almost all the calcium carbonate is derived from shell debris.
High percentages indicate that deposition in these regions is
Slow and that little sediment derived from land is deposited.

The highest values of organic carbon are found beyond

the shelf break. The distribution follows closely the

oe
: ee

by mide d
\ he

, a "1 f
: 3d Ylete Ee
alia ‘a
;
) ee dt ee nd Seo: fe ka fed 28
7 6 * "
ra 5 vA be Pus > &
- } f hy an L bb haha ‘-b.4
it . £

158

topography and sediment size indicating that organic particles
are selectively transported from nearshore and the topographic
highs and deposited in deeper water in the same manner as
detrital sediments. The high values near the Hyperion outfall
indicate that here there is a faster rate of deposition of
organic matter than can be oxidized, removed, or masked by
detrital sediment.

Cores and borings, especially those close to shore, show
extreme vertical variations in texture. These variations may
be due to many factors, including (1) fluctuations in quantity
of sediment reaching the bay from the watersheds and other
sources, (2) redistribution during periods of especially
strong turbulence in the bay or in periods of calms, (3) the
deposits may be related to former positions of sea level,

(4) formation of special topographic features or changes in
bottom topography, such as offshore bars, which may allow the
accumulation of unique deposits, and (5) slumping of sediments.

It is likely that many of the textural changes in the
cores from the submarine canyons are the result of slumping.

The clays and vegetation found in cores nearshore and
also in borings made on land close to shore are believed to
be due to deposition behind offshore bars. Landward migration
of sand from these bars may be the source of the sand in the

El Segundo Sand Hills.

adie ‘bak abadesotam itt ape , ets. nel
| “yilskosges) Ye ivobyeq pekaiet Aobiucix athoa: a)

9a 8) eemles te whokesq af aoqed wa he gemeanel 3
oy ers, “ytoves HD, te maz kt hao ote} 6? bete Catt ad tom

ae nz eogandy 70 eowtset Dkiqninogey cekoag ‘ jn
et wolfe Taw elo kab yezad aexomeily ap toe aridaatgoqoi
oy aamakbea Ww sige CU) baw eben supple to 0

‘A

‘bens snoiterses 2908 th ey aoktat Rey baa cate oft

neue

159

Relation of Transportation and Deposition of Sediment
to Discharge of Sludge into the Bay

Existing patterns of sediments in Santa Monica Bay
indicate that oceanographic conditions which cause the
deposition and transportation of the sediments may fluctuate
enough in some areas to create a condition of intermittent
deposition and removal of fine-grained material. This con-
dition seems to be especially true near the head of Santa
Monica Canyon and along the inshore side of the central
shelf projection where sands and silty sands are composed of
a relic coarse fraction plus a fine fraction deposited from
suspension. The preservation of relic material in these
surface sediments indicates that although the fine silt can
deposit here, often the sediments are reworked and most of
the fine material resuspended. This area is in the vicinity
of the end of the sludge outfall.

Currents in this portion of the bay flow toward shore
during most of the year. It is evident that particles of
sludge emanating from the end of the outfall which go into
suspension will move shoreward as they settle. However, it
is also important as a result of information collected on
sedimentation in the bay to recognize the possibility of
resuspension and further movement toward shore of any sludge
accumulating in these areas of the shelf. Thus, there is a
distinct possibility that sludge accumulating near the end of
the outfall and at a distance inshore might be carried pro-
gressively toward shore by repeated resuspension and current

motion and form a sludge deposit at a point intermediate

between the end of the outfall and shore.

ae elias na Sa,
. allie hO st @ oa +i .,

ie ia 1a! eee eee a tea alt a ae
Le ig wean: nee iia bait he spas, oes A

160
Areas of Rock Bottom

Rocks occurring in Santa Monica Bay are classified into
three groups; (1) bedrock, (2) gravel (transported rock), and

(3) phosphorite (a chemically precipitated rock).

Bedrock

The major area of bedrock exposed on the sea floor
occurs on the outer shelf pro jection between the two sub-
marine canyons, and rocks that are believed to be in place
occur off Malibu and the Palos Verdes Hills. The major
rock types found on the outer shelf are shales, but mud-
stones, siltstones, and sandstones also occur. Some of the
rocks have been dated as Miocene in age. Fragments of schist
recovered from the outer shelf are either basement rock
(Jurassic or older) or from a Miocene=-age breccia. Other
investigators have dredged rock from the Redondo or Santa

Monica Canyons.

Gravel

There are extensive patches of gravel in the nearshore
region, off Palos Verdes Hills, and near Malibu. Gravel in
extensive quantities is known to underly finer sediment in
other parts of the bay, but the full extent is unknown. Some
material of gravel size also occurs in the fine sediment of
the bay, but is widely dispersed. The gravel fragments are
primarily composed of igneous rocks with lesser amounts of
metamorphic and sedimentary material. The major gravel
deposit far offshore is surrounded by finer sediment, indi-

cating that it is relic and was not transported to this

ee tare
LOC atie ZF

‘
RY wits
ry lt Deel oy gel
ba) a SP ae

han

d maewolerg Wace
‘ ny) ; hes

ot Le Bae Tye uel 7 -
: Ph in, th
ren B Lela

Lee Aa
pin ein Yaste.

ce Gob
eo hat

ona
i

eR i

oh} Yee aa ke.
a ee | >

end by.

pons Ma a

aah hich

Nsae 36
Bipot Comte

161

location during the present cycle of sedimentation. It was
probably transported and deposited in the littoral zone during
a Pleistocene lowering of the sea. Its source was the bedrock
outcrops nearby and/or fluvial transport to its present
location by streams flowing from the east - presumably Ballona
Creek. The gravel is flanked by coarse-to medium-grained

sand containing a great proportion of rock fragments. These
rock fragment sands are thought to have been deposited at

the same time as the gravels.

Phosphorite

Phosphorite occurs in the sediment over the outer shelf
and on the outer edge of the shelf south of Redondo Canyon.
The presence of phosphorite is indicative of slow or non-

deposition of sediment in these areas.
Geologic Structure

The increase of the thickness of overburden in a shore-
ward direction from the central shelf projection indicates
that the bedrock area is high and that a trough exists near-
shore where great thicknesses of sediments have accumulated

| Two theories are presented to explain the geologic
structure of the outer shelf; (1) a continuation of the Palos
Verdes fault zone into the bay in which the outer shelf has
been uplifted in relation to the nearshore area, or (2) the
underlying consolidated rock dips gently toward shore with
bedrock exposed on the outer shelf.

The absence of schist among the rocks dredged from Santa

Monica Canyon by other investigators may indicate that the

4 it
A an

ange a snoie moat 7 _"

cpt Gps o k & td otqodee |

neuode ke ab msbardxov0 Yo oer std ‘0 paiee oor ;
aey eo bat pobsestio-ny Stene tentape git 90) woktverkb: baa )
mqner etetke Agnes w Pode bow alt eb aene aooxbed! nt ith
botalvnvons owed etmomhiog lo weapentokat: teary oisdw “a
atyolosg rr a migtaxs OF De ie@ery ose ao iroote owt:
(tole sdt to rokteuaetdnd a CL) 7 ebede etuo vote to’ onutoogte 1
tad dtede totue. ett abbas ud yad edt ofad oune stents asbuey ‘
adr (8) 20 ees MaReMAbe sdt OF eobtaew ab oe
sittw anode bsaves, ites eqih faon) beta bktokmoy | iiehinaat

| | tate rete a? mo bee |

ston tee heybisx aa oo% ate. gmoma, teidne be
ose tat disei sel Yam “azovepliaaymd xoitto

162

area north of the shelf projection has been down-faulted, or
tilted to the south.

The geologic structure of the bay is not considered to
be unique and faults are probably as numerous as on land. In
addition, it is likely that faulting is as active in the bay
as elsewhere in the southern California region. Although
there is no topographic expression of faulting on the shelf,
data strongly suggest one or more major faults. It is not
known whether the outfalls cross active subsurface faults.
However, since there is no surface expression of faulting
along the proposed outfall route, it may be presumed that no
vertical displacement will occur even if the faults are now
active.

Earthquakes resulting from movements along active faults,
either within the bay or elsewhere in the region, should be
regarded as probable. A long rigid outfall on unconsolidated

sediments may then be subjected to considerable stresses.

“4 Motte aie 0 5 edd twe'l Yo! wae zes aksgragoge? ‘
alice.

tom wh eT > yettwe? rotamr 3am 70 0 Toog eee at
eet toe pow Fasadie ovktaa ‘anarcy Mela ot eat

“on ants: Siecccyi atonal twos tuk tae
wae in atm ads 1 ween uEe tke o

; ay
Bs eat

SS 7

itive ovEton groks etapmovon not ttt navn “aateepainat
od Biugda ymalQos wht nt wrndwenty wa vaet ott mitt bw:

“ betabksouanoeu as bia Lowe :bighs wt A sidadoag 6a rs
sesneate biderebhenn2 op hetooldee ed month xual .

163
REFERENCES

Anonymous, 1916, Shore at Venice, California, best protected
by permanent sea wall and low groins: Eng. Record,
ve 73, no. 2, pe 36, 51-54 (rept. of Leeds and Barnard,
engineers).

Anonymous, 1917, Experiment with groins at Santa Monica Beach
successful. Wood and concrete structures are effectively
building up sand deposits: Eng. Record, v. 75, no. 13,
PeESOlasoa.

Anonymous, 1933, Santa Monica Breakwater: Shore and Beach,
Wo tbs ido Othe

Alden, J., 1856, Deposit of red sand inside of the bar of San
Francisco Bay, California: Ann. Rept. U. 5S. Coast
Survey, 8555 app. )20, pe 162.

Allison, L. E., 1935, Organic soil carbon by reduction of
chromic acid: Soil Sci., v. 40, p. 311-320.

Bache, A. D., 1852, Letter to the Secretary of the Treasury,
communicating information relating to Trinidad, Humboldt,
and San Diego Bays: Ann, Rept. U. S. Coast Survey 1851,
app. 50, p. 528=530.

Bache, A. D,, 1856, Letter from the Superintendent to the
Secretary of the Treasury, with copy of a communication
from Captain W. E. Call, Po. M.S. S. Columbia, and
extracts from a letter of Captain James Witkins, P. M.
S. S. Golden Age, relative to facilities for navigation
afforded by the development of a deposit of reddish sand
detected by Commander Alden inside of the bar at the
entrance to San Francisco Harbor, California: Ann. Rept.
U. S. Coast Survey 1856, app. 16, p. 119-120.

Bailey, T. L., 1943, Late Pleistocene Coast Range orogenesis
in southern California: Geol. Soc. America Bull., v. 54,
Do 1549-1568.

Bailey, T. L., 1954, Geology of the western Ventura Basin,
Santa Barbara, Ventura, and Los Angeles Counties:
Calif. Div. Mines Bull. 170, Map sheet no. 4.

Bailey, T. L., and Jahns, R. H., 1954, Geology of the Transverse
Range Province, southern California, in Geology of
Southern California, Chap. II, Geology of Natural Provinces:
Calif. Div. Mines Bull. 170, p. 83-106, 14 figs.

Beach Erosion Board, 1938, Beach erosion study at Ballona
Creek and San Gabriel River, California: Cooperating
agency State of California acting through the Los
Angeles Flood Control District.

Se : taisetona ‘teed skego tea. — da. rion 2101 200m
econ {owoet oases sq Weel ban t Layr 882). BS req uth -
‘ poe bes tte ‘ a 98 i ie Pian hae

‘dpoott ‘pont pene }
indeed og susan 4

Wut be Science ereL. mist 0
f Bow Das boow “Hee aoe
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164

Beach Erosion Board, 1948a, Littoral drift study, Los Angeles,
California: U. S. Army, Corps of Engineers, Beach
Erosion) Board Bull} v.)2, no. 3, p» 1-4.

Beach Erosion Board, 1948b, Review of reports on Redondo Beach
Harbor, appendix 6, shore-line effects: U. 5. Army, Corps
of Engineers, Los Angeles district.

Beach Erosion Board, 1948c, Report on survey of navigation
harbor at Playa del Rey, California: U. 5S. Army, Corps
of Engineers, Los Angeles district.

Beach Erosion Board, 1948d, Shoreline effects, harbor at
Playa del Rey, California. Enclosure 20 of report of
survey of harbor at Playa del Rey, California: U. S.
Army, Corps of Engineers, Los Angeles district, ii,
ol pe, Plo, maps, diagram.

Beach Erosion Board, 1948e, Shore-line effects, harbor at
Playa del Rey, California: U. S. Army, Corps of
Engineers, Los Angeles district. Enclosure 20
accompanying report on harbor at Playa del Rey,
California, dated Aug. 16, 1948, 51 p., 29 pls.

Beach Erosion Board, 1950a, Beach erosion control report of
cooperative study of the Pacific coast line of the state
of California, Point Mugu to San Pedro Breakwater: U. S.
Army, Corps of Engineers, Los Angeles district, Sept. 1.

Beach Erosion Board, 1950b, Appendixes 1 to 6, inclusive to
accompany beach~-erosion control report on cooperative
study of Pacific Coast line of the state of California,
Point Mugu to San Pedro Breakwater: U. S. Army, Corps
of Engineers, Los Angeles district, Sept. 1, app. l,
prior repts., 35 p.3 app. 2, description of the area,
36 p25 Lipl} appa 3; "eeolery, 52 p., 2 tables, 6 pis.3
app. 4, winds and waves, 13 p. including 3 tables,

3 pls.; app. 5, destructive waves along the southern
California coast, 22 p. incl. photos; app. 6, hydro-
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water escapes beneath the sea-level: Geog. Jour., v. 14,
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Briggs, C. R., and MacMillan, A. J., 1937, Beach processes
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Handin, J. W., 1951.

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165

Brongersma-Sanders, M., 1948, The importance of upwelling
water to vertebrate paleontology and oil geology: Verh.
konkl. Nederlandsche Akad. v. Wetensch. afd. Naturkunde,
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California Bureau of Sanitary Engineering, 1943, Report on a
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California Institute of Technology, Seismological Laboratory,
1934, Bulletin on Local Shocks,

Chace, B. w., 1953, Los Angeles County beach development :
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Clark, J. T., 1944, Index to descriptive catalog of earth-
quakes of the Pacific Coast of the United States, 1769-
1928: Seosmol. Soc. America Bull., v. 34, p. 35-62.
This is the index to the catalog by S. D. Townely and
M, W. Allen, published as v. 29 (1939), no. 1, p. 1-298,
of the Seismol. Soc. America Bull.

Clements, T., and Emery, K. O., 1947, Seismic activity and
topography of the sea floor off southern California:
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Cohee, G. v., 1938, Sediments of the submarine canyons off
the California coast: Jour. Sed. Petrology, v. 8,
pe 19-32,

Congressional Documents, 1897, 55th Cong., 1st sess., S. Doc.
18, 330 p., charts, pls., Deep-water harbor at Port
Los Angeles or at San Pedro, California.

Congressional Documents, 1949-50, , 81st Cong., 1st sess.,
H. Doc. 303, 37 pe, 2 charts, Redondo Beach Harbor,
Calif ornia.

Corey, W. H., 1954, Tertiary basins of southern California:
Calif. Div. Mines Bull. 170, Chap. III, p. 73-83.

Cotton, C. A., 1942, Shorelines of transverse deformation:
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Cotton, C. A., 1944, Glacial epochs of the Santa Monica
Mountains: a discussion: Jour. Geology, v. 52, p. 355-
S566

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166

Crowell, J. C., 1950, Submarine canyons bordering southern
Calafiornia: Geol. Soc. America Bull., v. 61, p. 1453-
1454 (abs.).

Crowell, J. C., 1952, Submarine canyons bordering central
and southern California: Jour. Geology, v. 60, p. 58-83.

Davidson, S., 1887, Submarine valleys on the Pacific Coast of
the United States: Calif. Acad. Sci. Bull., v. 2,
Po 265-268.

Davidson, G., 1897, The submerged valleys of the coast of
California, U. S,. A., and of Lower California, Mexico:
Calit. Acad. Scic Rroc., 3rd ser., geology, v. 1,

p. 73-103, 9 pis; Rev. by W. S. T. Smith, Jour. Geology
VES RGISOTOR ps 1533-534.

Davis, W. M., 1931, Shorelines of the Santa Monica Mountains,
California: Pan Am. Geologist, v. 55, p. 362-363 Cabs.);
Geol Soee America Bulli, (Proc. for 193815 iw. (43) €1932).
Deve27 Gabs a);

Davis, W. M., 1932, Glacial epochs of the Santa Monica Mountains,
Calaforniias Natl. Acad. Sei. Proc., v. 18, p. 659-665;
Geol. Soc. America Bull., v. 44 (1933), p. 1041-1133,
16 pls.; Pan Am. Geologist, v. 59 (1933), p. 306-307
(abs.); Nature, v. 131 (1933), p. 288 (abs.); Geol.
Soca Gmericarbull. proc. fom 1933, v.45 (1934), ip. 304—
305; Rev. in Geographical Rev., ve 24 (1934), p. 139.

Navas, Noo Mo, rutnam, Wo Gon and Richards, G. L., Jr.., 1930,
Elevated shorelines of the Santa Monica Mountains,
California: Pan Am. Geologists, v. 54, pe. 154 (abs.);
Geol. Soc. -America Bulls, proc. for 1930, v. 42 (1931),
De 309-310 (abs.).

Dietz, R. S., 1952, Geomorphic evolution of continental
terrace (continental shelf and slope): Am. Assoc.
Petroleum Geologists Bull., v. 36, p. 1802-1819,

Dietz, R. S., and Emery, K. O., 1938a, Phosphorite on the sea
floor off southern California: Am. Assoc. Petroleum
Geologists Bull., v. 22, pe 1717 Cabs.)).

Dietz, R. S., and Bmery, K. O., 1938b, Marine phosphate deposits
off the coast of California: Geol. Soc.,America Bull.,
ve 49, p. 1878, (abs.); Am. Assoc. Petroleum.Geologists
Bulticnive oops 177 Cabsia).

Dietz, R. S., Emery, K. O., and Shepard, F. P., 1942, Phos-
phorite deposits on the sea floor off souther California:
Geol. Soc. America Busters Veo 33\5 Po 815-848.

we
pe Pat

Me mmcet . ae pede | , to. ods. aes a

Pieitces ‘glk SP ou DRE eRe fe cl ae
#) ma yl \g

167

Dietz, R. S., and Menard, H. W., 195la, Origin on the shelf -
break: Geol. Soc. America Bull., v. 62, p. 1501 (abs.).

Dietz, R. S., and Menard, H. W., 1951b, Origin of abrupt change
in slope at continental shelf margin: Am. Assoc.
Petroleum Geologists Bull., v. 35, p. 1994-2016.

Driver, H. L, 1948, Genesis and evolution of Los Angeles Basin,
California: Am. Assoc. Petroleum Geologists Bull.,
Vemoe ype LOD=12)5)0

Drury, N. B., 1936, California's part in preserving shore and
beach: Shore and Beach, v. 4, p. 80-82.

Durrell, C., 1954, Geology of the Santa Monica Mountains, Los
Angeles and Ventura Counties: Calif. Div. Mines Bull.
170, map sheet no. 8.

Eckis, R., 1934, South coastal basin investigation; geology
and ground water storage capacity of valley fill: Calif.
Div. Water Res. Bull. 45, 273 p., 5 maps.

Emery, K. O., 1938, Rapid method of mechanical analysis of
sands: Jourc Sed. Petrology, v. 8, no. 3, p. 105-121.

Emery, K. O., 1941, Lithology of the sea-floor off southern
GCalatornias) Ph. Do ‘thesis, Univ. Fl.), Abs. thesis’ 3) p.

Emery, K. O., 1947, Phosphorite from the sea floor: Rocks
and Minerals, v. 22, p. 8-9.

Emery, K. O., 1952, Continental shelf sediments of southern
California: Geol. Soc. America Bull., v. 63, pe. 1105-
1108. 3

Emery, K. O., 1954a, General geology of the offshore area,
southern California: Calif. Div. Mines Bull. 170, Chap II,
pe 107-111.
= SS te

Emery, K. 0., 1954b, Some characteristics of southern California
sediments: Jour. Sedimentary Petrology, v. 24, p. 50-59.

Emery, K. 0., 1955, Grain size of marine beach gravels: Jour.
Geol., v. 63, now. 1, pe 39-49, 1 pl., 4 figs., 4 tables.

Emery, K. O., Butcher, W. S., Gould, H. R., and Shepard F. P.,
1952, Submarine geology off San Diego, California: Jour.
Geology, v. 60, p. 511-548.

Emery, K. O., and Dietz, R. S., 1950, Submarine phosphorite
deposits off California and Mexico: Calif. Jour. Mines
and Geology, v. 46, pe 7-15, 5 pls.

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168

Emery, K. O., and Foster, J. F., 1948, Water tables in marine
beaches: Jour. Marine Research, V. 7, P. 644-654

Emery, K. O., and Rittenberg, S. C., 1952, Early diagenesis
of California basin sediments in relation to origin of
oil: Am. Assoc. Petroleum Geologists Bull., v. 36,
pe 735-806

Emery, K. O., and Shepard, F. P., 1941, Lithology of the sea
floor off southern California: Geol. Soc. America Bull.,
ve 52, Pe 1899-1900 (abs. )

Emery, K. O.,y and Terry, R. D., 1956, A submarine slope of
southern California: Jour. Geol., V. 64, P. 271-280

Emery, K. O., and Shepard, F. P., 1945, Lithology of the sea
floor off southern California: Geol. Soc. America Bull.,
Ve 56, Pe 431-478

Fairbridge, R. We, 1947, Coarse sediments on the edge of the
continental shelf: Am. Jour. Sci., V. 245, p. 146-153

-Fleming, R. H., 1937=38, Tides and tidal currents in the
Gulf of Panama: Jour. Marine Research, V. 1, P. 192-206

Fleming, R. H., and Revelle, R., 1939, Physical processes
in the oceans, in Trask, P. D., Recent marine sediments,
Symposium pub. by Am. Assoc. Petroleum Geologists,
Tulsa, Okla., p. 48-141

Frasher, C. McL., 1943, General account of the scientific
work of the VELERO III in the eastern Pacific, 1931-41;
Part III. A ten-year list of the VELERO IIIcollecting
stations including an appendix of collecting stations
of the Allan Hancock Foundation for the year 1942;
Los Angeles, Univ. Southern Calif. Press, Allan Hancock
Pacific Expeditions, V. 1, No. 3, p. 259-431, incl. 15
charts.

Goldberg, Jo, 1940, The geological significance of the coastal
terraces of the Santa Monica Mountains: M. A. thesis,
Univ. Calif., Los Angeles, 133 p., 18 pls, 3 figs.,

Grant, U. S., 1938, Geological problems involved in the
conservation of beaches: Pacific Southwest Acad. Pub.
16, p. 27-28

Grant, U. S., 1943, Waves as a sand-transporting agent: Am.
Jour. Sci., V. 241, p. 117-123; Shore and Beach, V. 11
pe 46-48, 52.

Grant, U. S., 1946, Effect of ground-water table on beach
erosion: Geol. Soc. America Bull., V. 57, pe 1252 (abs.).

ray Ee,
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Grant,

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Hall,

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169

U. S., 1955, The relation between amount and character
of beach sand and denudation rate in source areas:
Pacific Petrol. Geologisit, v. 9, nos 5.

U. S., and Shepard, F. P., 1937, Changes along the
California coast: Geol. Soc. America Bull., proc. for
UOSGy Wie c4Sig GD OK), Cabs! >’.

U. S., and Shepard, F. P., 1938a, Short-period oscilla-
tions of southern California beaches and adjacent sea
filloor: (Geol sec. America Bull.,, proc. for 1937, v.49,
pe 84-85 (abs.).

U. S., and Shepard, F. P., 1938b, Magnitude of some
shore processes in southern California: Geol. Soc.
America Bull, proc. for 1937, v. 49, pe 239-240 (abs.).

U. S., and Shepard, F. P., 1946, Effect of type of wave
breaking on shore processes: Geol. Soc. America Bull.,
Wo Sly M5 se (Goose ps

n,:D.,R., 1944, Coastline plans and action for the
development of the Los Angeies metropolitan coastline:
Los Angeles, Haynes Foundation, 38 p. incl. illus.

Cre enichiten Celis s)anGdmWood), Hi.) Os ihOS2)suhe
earthquake in Santa Monica Bay, California, on August
$0, 1930: Seismol. Soe. America Bull., v. 22), p. 138-=
1S. pS. Wh, ie,

Je Ve, Jre, 1952, Artificially nourished and constructed
beaches: U. S. Army, Corps of Engineers, Beach Erosion
Board, Tech. Memo 29, 25 p.; Third Conf. Coastal Eng.,
Berkeley, (1953), p. 119-136..

» Je W., 1949, The source, transportation and deposition
of beach sediment in southern California: Ph. D. thesis,
Unive.) Calitvy Eos Anreles, Ou7sipe, L2 eplisas UsS Army,
Corps of Engineers, Beach Erosion Board Tech. Memo. 22,
Gost) LZaokp. sine 2 etablesh. 2) plist.

nie We, and) Cudwaick, jin) GC.) 1949),) Accretion) of beach
sand behind a detached breakwater: Scripps Inst.
Oceanography, Submarine Geology Rept. no. 8, 15 Pe,

1 pl., 1 fig.; U. S. Army, Corps of Engineers, Beach
Erosion Board Tech. Memo. 16 (1950), 13 p.

N. H., 1947, List of seismic sea waves: Seismol. Soc.
America Bulll., v. 37, ps 269-287. (First pub. in
Internat. Geod. and Geophys. Union, Comm. pour. 1'Elude
des Raz de Maree, no. 4 (1934), p. 20-41).

M, L., 1954, Tectonics of faulting in southern California:
Calafiy Divo Mines Bull.) 170),. Chap. IV; .p. S=13%

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170

Hill, R. T., 1928, Southern California geology and Los
Angeles earthquakes: Los Angeles, Pub. by Southern
Calf Acad. ocinnecoce De, Lllus., 4uplsi.

Hjulstrom, F., 1939, Transportation of detritus by moving
water, in Recent Marine Sediments, pub. by Am. Assoc.
Petrol.eGeole., tulsa, Ola. pe S—Sai.

Hoots, H. W., 1931, Geology of the eastern part of the Santa
Monica Mountains, Los Angeles County, California: U. S.
Geol. Survey Prof. Paper 165-C.

Inman, D. L., 1949, Sorting of sediments in the light of
fluid mechanics: Jour. Sed. Petrology, v. 19, p. 51-70.

Inman, D. L., 1952, Measures for describing size distribution
of sediments: Jour. Sed. Petrology, v. 22, p. 125-145.

Inman, D. L., 1954, Beach and nearshore processes along the
southern California coast: Calif. Div. Mines Bull. 170,
Chap. V, pe 29-34.

Jenkins, J. T., 1921, A textbook of oceanography: Constable & Co.,
London.

Johnson, A. G., 1935, Beach protection and development around
Los Angeles: Shore and Beach, v. 3, pe 110-113.

Johnson, A. G., 1940a, A report on protection and development
of the beaches in the Westgate addition and Santa
Monica Canyon addition: Los Angeles Dept. Public Works,
Bur. One Eneic . wADr vl.

Johnson, A. G., 1940b, A report on erosion of the beaches in
the Venice district: Los Angeles Dept. Public Works,
BurOt Engin, April.

Johnson, A. G., 1940c, Southern California beach erosion.
Problems aggrevated by unwise man-made structures and
lack of centralized controls Shore and Beach, v. 8,
pes LO6=109, 120, 121".

Johnson, A. G., 1951, Santa Monica Bay shoreline development
plans, in Proc. First Conf. Coastal Eng., pub. by
Council on Wave Res., Univ. Calif., Berkeley, p. 271-
ple, GS esterC\,

Kelley, V. C., 1932, Geology of the Santa Monica Mountains
west of the Malibu Ranch, Ventura County, California:
Master's thesis, Calif. Inst. Tech.

Kenyon, E. C., Jr., 1951, History of ocean outlets, Los Angeles
County Flood Control District: Firs Conf. on Coastal
Eng., Berkeley, p. 277-282.

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171

Kerr, A. R., 1938, Littoral erosion and deposition of Santa
Monica Bay: M. A. thesis, Univ. Calif., Los Angeles,
49 pe, anew. tables. SO) pls.

Krumbein, W, C., 1941, Measurements and geological significance
of shape and roundness of sedimentary particles: Jour.
Sed) Petrology venlh, pe 64—72.

Krumbein, W. C., and Pettijohn, F. J., 1938, Manual of sedi-
mentary petrography: Appleton-Century-Crofts, Inc.,
New York, 549 p.

Krumbein, W. C., and Sloss, L. L., 1953, Stratigraphy and
sedimentation: W, H. Freeman & Co., San Francisco,
497 De

Kuenen, P. H., 1939, The cause of coarse deposits at the
outer edge of the shelf: Geologie en Mijnbouw, le Jr.,
No E65 1@6 Bo fos WOSsIs

Lapsley, W. W., 1937, Sand movement and beach erosion: M. S,
thesis, Univ. Calif., Berkeley, 27 p. + app. 9 p.,
8 pls., photos p. 10-16. (includes model studies of
Santa Barbara and Santa Monica).

Larsen, G. P., 1939, Santa Monica Beach, California: Shore
andwBeachi wand, mDet lool.

Larsen, G. P., 1942, Breakwaters along the California coast:
Shore and Beach, v. 10, p. 69.

Layne, J. G., 1935, Annals of Los Angeles, 1769-1861: Calif.
Historical soOC Eo pecen bub.) OO.) Oy pe all—do.

Leeds, C. T., 1916, Shore protection at Venice, California.
General statement of damage which has been done: Prof.
Mem., U. S. Army, ‘“orps of Engineers, v. 8, no. 37,
Pp. 42-58, diagrams, folded pls.

Livingston, A., Jr., 1939, Geological journeys in southern
California: Dubuque, Iowa, 2nd ed., Wm. C. Brown Co.,
USE Poo 5 SHES Mee eels jaz Js UeniebresGieeye) ies ebavel Wig (Ge
Putnam, 1933, Pub. no. 1, Los Angeles Jr. College,
Geol Sete Viemlne 104. Diese dels.

Longwerl, CG. R., Knopf, A., and Filant, R. F., 1950, Physical
geology: John Wiley & Sons, New York, 602 p.

Los Angeles County Flood Control District, 1948, Biennial
report on hydrological data, seasons of 1945-46, and
1946-47: Unpub.

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172

Los Angeles County Regional Planning Commission, 1938, Marina
del Rey. Report on proposed harbor at Playa del Rey: June.

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Be Nia

af ; ron ent

L738

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174

Revelle, R., and Shepard, F. P., 1939, Sediments off the
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2 tables.

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| a ea Ps %
A abc ay an? ue hes

175

Shepard, F. P., 1951, Mass movements in submarine canyon
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176

Trask, P. D., 1952, Source of beach sand at Santa Barbara,
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S mye | Py oe

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U. S. Waterways Experiment Station, Vicksburg, Mississippi,
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Dec. 127

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Wheeler, G., 1936, Davis's study of California marine terraces:
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Woodring, W. P., Bramlette, M. N., and Kew, W. S. W., 1946,
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Woodring, W. P., Bramlette, M. N., and Kleinpell, R. M.,
1936, Miocene stratigraphy and paleontology of the
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Woodring, W. P., and Kew, W. S. W., 1932, Tertiary and Pleis-
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Zalesny, E. R., 1956, Foraminiferal ecology of Santa Monica
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Zielbauer, E. J., and Davis, R. S., (undated), Geologic
studies relative to investigational work for prevention
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Flood Control District, appendix A., 17 p., + pls.

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