CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
SEISMIC STRATIGRAPHY AND FAULT ACTIVITY
OF THE INNER SAN PEDRO SHELF, CALIFORNIA
A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in
Geology by
Madeline Marie Woods
August, 1984

The Thesis of Madeline Marie Woods is approved:
California State University, Northridge i i

Acknowledgments
The author is grateful to Dr. Peter Fischer of Caliornia State University, Northridge, for suggesting this study. Dr. Fischer, along with Dr. Donn Gorsline of the
University of Southern California and Dr. Gerald Simila of
California State University, Northridge, reviewed the manuscript and provided many helpful suggestions. Special thanks are extended to the crew of the R/V Nautilus for assistance in data collection, and to Charles Chamberlain for assistance with photography. i i i

TABLE OF CONTENTS
PAGE
ACKNOWLEDGEMENTS •••••••••••••••••••••••••••••••••••••••• i i i
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ===
.vi
LIST OF TABLES •••••••••••••••••••••••••••••••••••••••••• vii
LIST OF PLATES •••••••••••••••••••••••••••••••••••••••••• vii
ABSTRACT ••••••••••••••••••••••••••••••••••••••••••••••• viii
CHAPTER
1. INTRODUCTION ••••••••••••••••••••••••••••••••••••••••• 1
GENERAL STATEMENT ••••••••••••••••••••••••••••••••• 1
PREVIOUS WORK ••••••••••••••••••••••••••••••••••••• 4
2.
3.
REGIONAL GEOLOGY •••••••••••••••••••••••••••••••••• 6
TECTONIC SETTING ••••••••••••••••••••••••••••••••• 12
METHODS AND PROCEDURES •••••••••••••••••••••••••••••• 17
INTRODUCTION ••••••••••••••••••••••••••••••••••••• 1 7
GEOPHYSICAL SURVEYS •••••••••••••••••••••••••••••• 1 7
CSUN SURVEYS ••••••••••••••••••••••••••••••••••• 17
CERC SURVEY •••••••••••••••••••••••••••••••••••• 21
USGS SURVEY. • • • • • • • • • • • • • • ••••••••••••••••••••• 2 2
DAMES AND MOORE SURVEY •••••••••••• o • • o • • • • • • • • •
22
DATA REDUCTION AND INTERPRETATION •••••••••••••••• 23
STRATIGRAPHY •••••••••••••••••••••••••••••••••••••••• 2 5
INTRODUCTION •••• o • • • • • • • • o • • • • • • • • • • • • • • • • • • • • • • •
25
BASEMENT ROCKS ••••••••••••••••••••••••••••••••••• 28
MIOCENE •••••••••••••••••••••••••••••••••••••••••• 32
PLIOCENE ••••••••••••••••••••••••••••••••••••••••• 3 3 iv
(I '

TABLE OF CONTENTS (Continued)
PAGE
3. STRATIGRAPHY (continued)
PLEISTOCENE ••••••••••
. . .. . . . . . . . . . . . . . . . . . . . .
.35
LOWER PLEISTOCENE •••••••••••••••••••••••••• 37
UPPER PLEISTOCENE •••••••••••••••••••••••••• 42
UNNAMED DEPOSITS AND LP IV ••••••••••••••• 47
LP I I I 50
LP I I . . • • • . • . • . • . • . • • • • • • . • . • . . . . . . • • • . • . 51
LATE PLEISTOCENE CHRONOLOGY ••••••••••••••••••••• 54
HOLOCENE • ••••••••••••••••••••••••••••••••••••••• 58
4. STRUCTURE •••••••••••••••••••••••••••••••••••••••••• 62
FAULTING • •.••••.•••••••••.•••••••••••.•••.• e • ••• 62
5. NEOGENE EVOLUTION OF THE SAN PEDRO SHELF ••••••••••• 69
6 • SUMMARY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • til 8
a • •
= = = 8 0
7 • REFERENCES • •••••••••••••••••••••••••••••••••••••••• 84
Q ' v

List of Figures
PAGE
1 . Index Map. . . . . . . . . • . . . . . • . . . . . . . . • . . • . . . . . . . . . . . . 2
2. Major Structural Features of the Los Angeles
Basin and Surrounding Area •••••.••••••••••••••• 3
3. Gaps and Mesas along the Newport-Inglewood
Zone of Deformation ••••••••••••••••••••••••.••• 9
4. Major Faults in Southern California •••••••••••••• l3
5. Earthquake Epicenters in the Los Angeles Basin and Surrounding Area •••••••••••.••••••••••••••• l6
6. Location of Rotary Borings and Vibratory
Corings on the San Pedro Shelf •••••••.••••••••• 20
7. Cenozic Stratigraphic Correlation Chart •••••••••• 26
8. Sparker Line 445 (USGS) •••••••••••••••••••••••••• 36
9. Sparker Line 449 (USGS) •••••••••••••••••••••••••• 40
10. Sparker Line 453 (USGS) •••••••• •••••••• •••••••• •• 41
11. UN I BOOM Line 455 (USGS) •••••••••••••••••••••••••• 4 3
12. Sparker Line SA (Dames & Moore) •••••••••••••••••• 48
13. UNIBOOM Line 455 (USGS) •••••••••••••••••••••••••• 49
14. Acuray Line A-G (CERC) ••••••••••••••••••••••••••• 52
15. UNIBOOM Line 4A (Dames & Moore) •••••••••••••••••• 53
16. Acuray Line A-5 (CERC) ••••••••••••••••••••••••••55
17. Quaternary Sea Ley51 reuctuations and their
Corresponding 0 /0 Stages ••••••••••••••••••• 56
18. Acuray Line A-G (CERC) ••••••••••••••••••••••••••• 60
19. Cross Section A-A' ••••••••••••••••••.•••••••••••• 64
20. Aquapulse Line SW 8 •••••••••••••••••••••••••••••• 66
21. Acuray Line A-G (CERC) ••••••••••••••••••••••••••. 68
22. A Rotational Model for Southern California
Tectonic History •.••••••••.•••••••••••••••••••• 71 vi
0 .

I
II
List of Plates
(in pocket)
Trackline Map - CSUN and CERC Data (1:24,000)
Trackline Map - USGS, Dames and Moore, and
Western Geophysical Data (1:24,000)
III Structure Contour Map of the Top of the Upper
Pliocene (Pice Formation) (1:24,000)
IV Structure Contour Map of the Top of the Lower
Pleistocene (San Pedro Formation) (1:24,000)
V
VI
Isopach Map of Holocene Sediments (1:24,000)
Geologic Map of the San Pedro Shelf with
Holocene Overburden Removed (1:24,000)
List of Tables
PAGE
1. Seismic Profile Data Summary •••••••••••••••••••••••• l8
2. Equipment Specifications •.••••.••.•••••••••••••••••• l9
3. Detailed Stratigraphy of the San Pedro Shelf and
Onshore Correlatives •••••••••••••.••••••••••••••• 29
4. Age Dates of Pleistocene Sediments in the vicinity
of the Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 vii

ABSTRACT
SEISMIC STRATIGRAPHY AND FAULT ACTIVITY
OF THE INNER SAN PEDRO SHELF, CALIFORNIA
Madeline Marie Woods
Master of Science in Geology
As part of the southern California Continental Borderland, the San Pedro Shelf represents the southwestern extension of the Los Angeles Basin. The wide configuration of the shelf is predominantly a function of tectonic activity and the resulting sedimentation patterns. The major structural features of the San Pedro Shelf are the Palos
Verdes uplift and Palos Verdes fault, the Wilmington
Graben, and the offshore extension of the Newport Inglewood
Zone of Deformation.
Pliocene sediments of the Wilmington Graben consist of the Repetto and Pico Formations. Cumulative thickness of these formations ranges from tens of meters in the inshore viii

area to hundreds of meters in the axis of the graben.
Quaternary sediments consist of the lower Pleistocene San
Pedro Formation, a series of upper Pleistocene deposits designated LP IV through LP II, and Holocene sediments.
The upper Plesitocene units represent stratigraphic sequences and they have been correleted to published sea level fluctuation curves and corresponding oxygen isotope stages.
A series of faults corresponding to faults mapped by Junger and Wagner ( 1977) have been identified on the shelf. These faults, which bound the landward edge of the
Wilmington Graben, do not disrupt sediments younger than lower Pleistocene. I t is suggested that the faults became inactive when the right-lateral shear regime of the present-day Newport Inglewood fault took effect in early
Pleistocene time. I t is possible that these faults represent an old branch of the Newport Inglewood fault.
Two active (?) faults offshore of Newport Beach are believed to represent offshore extensions of the Newport
Inglewood Zone of Deformation. Recent activity on this zone is also evidenced by recent structural growth on the
Huntington Beach anticline. Sedimentation patterns of the Pleistocene units imply continued uplift of the anticlinal structure during the depositional periods. Several minor faults exhibiting upper Pleistocene deformation are mapped on the southern flank of the anticline. These faults trend northeast-southwest and show evidence of movement in late Pleistocene time. xi

1. INTRODUCTION
General Statement
This study was undertaken to investigate a series of faults southwest of the Newport-Inglewood Zone of
Deformation (NIZD) along the inner San Pedro Shelf, California. The purpose of the study was to develop a model that would elucidate the neotectonic relationship among the
Newport Inglewood Zone of Deformation (NIZD), the Palos
Verdes fault zone, and the above mentioned faults in light of the Pliocene-Quaternary evolution of the San Pedro
Shelf.
The study area is located off southeastern Los Angeles
County and southwestern Orange County, California (Figure
1). To the north and northeast i t is bounded by the coastline, to the west and southwest by the Los Angeles-Long
Beach breakwater, to the southeast by the Newport canyon, and to the south by the 25- to 30-meter isobaths.
As a southwestern extension of the Los Angeles Basin
(Figure 1), the San Pedro Shelf has been active tectonically since the inception of the basin in middle Miocene time (Nardin and Henyey, 1978). The series of faults examined in this study have been previously mapped by
Junger and Wagner (1977). As mapped by these authors, the faults extend from offshore Seal Beach to a point south of
Huntington Beach (Figure 2) • An exact age of the fault activity was not determined, but a general age of late
Pliocene was noted by these authors.
1

30'
TRANSVERSE RANGES
LOS ANGELES BASIN
118°
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CALIFORNIA
CONTINENTAL
BORDERLAND
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FIGURE 1 INDEX MAP OF THE STUDY AREA
PENINSULAR RANGES
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FIGURE 2 - MAJOR STRUCTURAL FEATURES OF THE LOS ANGELES BASIN AND SURROUNDING AREA w

Immediately onshore from the study area is the Newport-Inglewood Zone of Deformation (NIZD), a prominent structural feature of the basin area. This zone has been studied extensively by the petroleum industry because anticlinal structures of the zone, along with a series of en echelon faults, have produced significant stratigraphic oil and gas traps (Yeats, 1973). The seismicity of this area has also been monitored closely as the zone has proven active during late Pleistocene-Holocene time (Barrows,
1974: Hileman and others, 1973). The largest earthquake attributed to the zone was the Long Beach earthquake of
1933, which registered 6.3 on the Richter scale with an approximate epicenter 5. 5 km southwest of Newport Beach
(Barrows, 1974: Dames and Moore, 1977).
Extending south from offshore Laguna Beach to Oceanside is the offshore extension of the NIZD, also referred to as the South Coast Offshore Zone of Deformation (SCOZD)
(Woodward-Clyde Consultants, 1979). This fault consists of a series of non-continuous, right-lateral, strike-slip faults on trend with the NIZD.
Previous Work
Early studies of the continental borderland by .. Shepard and Emery (1941) and
~m~~y
(1954, 1960) were peri6r~ed using only bathymetric profiles and rock dredge samples.
Moore (1954) utilized these same kinds of data to study unconsolidated sediment distribution and characteristics on
4

the San Pedro Shelf. In 1960, Moore initiated the use of subbottom reflection profiles for a study of the
California continental borderland.
Improvement of seismic reflection techniques yielded more detailed studies of the geology of offshore areas.
Bechtel (1967), using sparker and arcer profiles along with sediment borings, mapped a portion of the inner San
Pedro Shelf in a site evaluation study for a proposed combination power and desalination plant. A reconnaissance study of the geology of the borderland was completed by Vedder and others (1974) using deep penetration sparker data, magnetic and gravimetric data, and sediment samples.
In preparation for offshore lease block sales, Greene and others (1975) evaluated the San Pedro Shelf and other selected borderland areas for geologic hazards. Deep penetration sparker and high resolution profiles were used by Junger and Wagner (1977) to map the geology of the
Santa Monica and San Pedro Basins. Nardin and Henyey
( 1978) completed a study of the Pliocene-Pleistocene diastrophism of the Santa Monica and San Pedro Shelves, analyzing geophysical profiles along with jet and dart core samples.
Recently, several smaller scale studies were completed on the San Pedro Shelf. Lee (1977) mapped the offshore extension of the Newport-Inglewood fault zone and also analyzed the grain size and trace metal geochemistry of the surface sediments in the Newport canyon vicinity. Detailed
5

studies of recent activity and earthquake capability of the extension of the Palos Verdes fault on the San Pedro shelf were completed by Dames and Moore Consultants (1977),
Darrow and Fischer (1983), and Fischer and others (1984).
The preliminary seismic stratigraphy of this area has been established by several workers. As part of a geophysical and geotechnical platform site evaluation, Fischer and others (1977) proposed a Late Quaternary model for the outer San Pedro Shelf (OCS tracts 261-262). Rudat (1980) and Rudat and others (1984) extended this seismic stratigraphic model to the inner San Pedro Shelf, incorporating with i t the Late Quaternary evolution of the shelf.
Regional Geology
Coastal southern California comprises portions of three geomorphic provinces: the Coast Ranges, Transverse
Ranges, and the Peninsular Ranges. All three of these provinces extend offshore and the study area lies within the submerged portion of the Peninsular Ranges (Figure 1).
The offshore counterpart of the Peninsular Range province has been termed the California Continental Border.land ( CCB) by Shepard and Emery (1941).
In the Peninsular Ranges, northwest-southeast trending fault zones divide the province into roughly parallel block faults establishing the predominant structural style of the area (Mayuga, 1968). The northwest-southeast trending Palos Verdes Hills and the coastal plain, including the
6

Los Angeles Basin, are the distinct geomorphic units of the area. The Los Angeles Basin lies at the north end of the
Peninsular Ranges: the basin structurally extends offshore as the Santa Monica and San Pedro Shelves (Junger and
Wagner, 1977). It is bounded to the north by the Santa
Monica and San Gabriel Mountains, to the east by the Santa
Ana Mountains, and to the west and south by the Palos
Verdes Hills and the Pacific Ocean The basin originated in early mid-Miocene time, and is believed to have begun as a pull-apart structure over a "hot-spot" that was associated with the East Pacific Rise (Crowell, 1974).
The Los Angeles Basin floor is presently buried beneath 7,000 meters of Miocene and post-Miocene sedimentary rocks (Woodford and others, 1954). The southwestern section of the basin is underlain by a glaucophane schist
(Catalina Schist); the northern and eastern sides of the basin are underlain by pre-upper Cretaceous crystalline rocks. These two basement complexes are juxtaposed along the Newport-Inglewood Zone of Deformation (NIZD), the prominent structural feature of the basin area.
The NIZD is marked by a northwest trending series of en echelon faults and shallow drag anticlines, expressed as low hills and mesas, extending from Beverly Hills to
Newport Bay (Yerkes and others, 1965) (Figure 2). To the northwest the fault zone terminates at the Santa Monica fault zone: to the southeast i t extends offshore as several splay faults that appear to terminate against the offshore
7

extension of the San Joaquin structural high (Woodward
Clyde Consultants, 1979). Approximately 24 separate faults of significant displacement are associated with the NIZD.
Several of these break the surface where they form topographic escarpments in the Pleistocene alluvial materials
{Barrows, 1974). Displacement on these faults is dominantly right-lateral, however, some exhibit normal, reverse, or left-lateral displacement where faults are associated with major folds. The numerous anticlinal folds along with the diverse fault patterns of the basin sediments along the NIZD are apparently a result of deep-seated wrench faulting.
The Huntington Beach anticline, a part of the NIZD, extends onto the San Pedro Shelf directly southwest of
Huntington Beach. This feature trends east-west and has had a large impact on the Pleistocene and Holocene sedimentation patterns of the shelf.
Six gaps are incised in the low hills and mesas of the
NIZD. From northwest to southeast, they are: Ballona,
Dominguez, Alamitos, Sunset, Bolsa, and Santa Ana {Figure
3) (Poland and others, 19 56) • These gaps are believed to have been stream-cut into the late Pleistocene surface and later deformed.
As previously stated, the Palos Verdes Hills form the southwestern border of the Los Angeles Basin. The hills have a maximum elevation of 450 meters. They are characterized by a rolling topography in the upper portion
8

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FIGURE 3 LOCATION OF GAPS AND MESAS OF THE COASTAL AREA
1..0

{Moore, 1954). Thirteen terraces have been recognized on the Palos Verdes Hills, implying successive periods of uplift {Woodring and others, 1946). These terrace levels, along with the presence of warped late Pleistocene terrace deposits along the northeast side of the hills, suggest continuing recurrent deformation of this area (Bechtel,
1967).
Two anticlinal structures are present in the Palos
Verdes-Long Beach area (Figure 2) . The Wilmington anticline, located just north of the Palos Verdes Hills, has a total length of approximately 30 kilometers: it has a core of Catalina schist that is overlain by 3,500 meters of
Neogene sediments (Junger and Wagner, 1977). The Palos
Verdes Hills anticline underlies the Palos Verdes Hills, extending both northwest and southeast into the offshore area for a total length of approximately 70 kilometers
(Junger and Wagner, 1977: Nardin and Henyey, 1978). This anticline is faulted on the northeast flank by the Palos
Verdes Hills fault, which strongly tilts and folds Pleisto-
I cene and older strata.\
~
Palos Verdes Hills fault is a steeply dipping reverse fault with considerable dip slip and notable components of strike-slip displacement (Yerkes and others,
1965: Bechtel, 1967). The fault extends northwest into the
Santa Monica Bay, where i t is thought that the Redondo
Canyon fault abuts i t near Redondo Beach (Nardin and
Henyey, 1978). To the southeast i t extends into the San
10
0 •

Pedro Bay where i t juxtaposes the nearly-horizontal beds of the Wilmington Graben with the steeper dipping beds of the
Palos Verdes Uplift.
[:he San Pedro
Shel~J ranges in width from 200 kilometers south of Long Beach to less than 2 kilometers south of the Palos Verdes Peninsula. The shelf~as been divided into two separate structurally controlled sections, the
Palos Verdes Uplift and the Wilmington
(Figure 2)
(Junger and Wagner, 1977). As stated before, the Palos
Verdes Uplift is controlled by the offshore extension of the Palos Verdes Hills fault. The Wilmington Graben contains a thick section of upper Pliocene and Quaternary sediments. As proposed by Junger and Wagner (1977), it is a downdropped block, bounded to the south by the Palos
Verdes fault, and to the north by a discontinuous series of
==--..,_~1 faults.
I
The Newport submarine canyon is incised into the southeast edge of the San Pedro shelf. Water depths in the canyon exceed 100 meters and the bathymetric slopes average
9% (5.1 ) along the canyon walls. This canyon is the seaward expression of the Santa Ana River, which presently discharges approximately five kilometers northwest of the canyon head. Felix and Gorsline (1971) believe the canyon has formed at a point where the shelf is narrow and sand moved by longshore drift is concentrated at a convergence zone.
11
(l '

TECTONIC SETTING
San Andreas Fault System
The southern California area, including the California
Continental Borderland (CCB), is dominated tectonically by right-lateral, strike-slip faulting. The major structural feature of the area is the San Andreas fault system, and i t represents the general boundary between the Pacific and
North American plates. The actual boundary between the two plates is most probably a wide, ductile boundary, represented by western North America (Atwater, 1970). Both the San
Andreas and the San Jacinto fault zones, which are northwest trending, right-lateral faults, comprise the San
Andreas fault system (Woodward-Clyde Consultants, 1979).
This system is paralleled to the west by other smaller scale, right-lateral fault zones, such as the Whittier-
Elsinore, Newport-Inglewood, and San Clemente fault zones
(Figure 4).
The San Andreas fault system is believed to have initiated approximately 30 million years ago (Atwater,
1970). Prior to this, in middle Tertiary time, subduction was actively occurring off western North America. The right-lateral shear couple between the North American and
Pacific plates was initiated when the east Pacific rise encountered North America.
While determining relative positions of the Pacific and North American plates, Atwater and Molnar (1973)
12

0
Scale
0~~~~~5~0~~~~1::;00
Miles
50 100 150 Kms.
Modified from Albee and Smith ( 1966)
FIGURE 4 MAJOR FAULTS IN SOUfHERN CAUFORNIA
13

established plate rates and motions for the last 30 million years. The present rate between the Pacific and North
American plates is 5.5 centimeters/year.
The smaller faults that parallel the San Andreas fault system are presumably responsible for some of the strain release of this system. However, the faults to the west, including those mapped in this study, show an apparent progressive westward decrease in total displacement, continuity of surface trace, and earthquake activity. This is evidenced by the following strike-slip displacement values compiled by Woodward-Clyde Consultants (1979).
Feature Total
Displacement
(km)
San Andreas 480 to 700
San Jacinto 5.2 to 24
8 to 13
Age of
Displaced
Units
Cretaceous to
Miocene
Source
Hill-Hobson,
1968; Ehlig and others,
1975
Post Cretaceous to Middle
Pleistocene
Sharp, 1967,
1978
Tertiary Weber, 1977 Whittier-
Elsinore
Newport-
Inglewood
3 Late Miocene Hill, 1971
The decrease in total displacement also indicates a slower geologic slip rate. This pattern suggests an eastto-west gradient in strain from the inception of the present strain regime in Miocene time to the present (Woodward Clyde
14

Consultants, 1979). Earthquake epicenters for Los Angeles. and the surrounding area support this east-to west gradient strain pattern (Figure 5).
15
I .

(') i
THOUSAND OAKS
0 l[) cD
&' lf1
N
CD
0
0 cD l[)
['-r-:
0
\f) r-
+
L;)
N
-
['--
I
0
0
-
['--
I
+
I +
34. 5.D
LEGEND
REPORTED EARTHQUAKE MAGNITUDES rTJ
I
)
8.0
( j l
'
'
7.0
0
6.0
C)
5.0 r2)
Q)
4.0
3.0
Richter magnitude symbol sizes are shown on a continuous nonlinear scale.
The epicenters cover the time period 1918 through 1982. Data source: National Oceanic and Atmospheric Hypocenter Data File, 1983.
Only epicenters with magnitudes greater than
3.5 are shown.
16
(')
(')
PIP
33. s::. u
(')
\
\
\
\
\
\
\
\
\
\
\
(')
\
\
\
\
\
\ \
EARTHQUAKE EPICENTERS
IN THE LOS ANGELES BASIN
AND SURROUNDING AREA
FIGURE 5

2. METHODS AND PROCEDURES
Introduction
The major portion of the data base for this study was provided by seismic reflection profiling. A total of 1,080 line kilometers of seismic data were obtained (Table 1).
The types of data included: side-scan sonar, 3.5 kHz high resolution, Uniboom, shallow and intermediate penetration sparker, and Common Depth Point (CDP) (Table 2, Plates I and II). Reflection profiles were examined and correlated with existing onshore well data (State of California,
Division of Oil and Gas, 1961) and offshore corehole data available (Bechtel, 1967; Lee, 1977; Fischer and others,
1977). Also incorporated were available vibracore data obtained from the Coastal Engineering Research Center
(CERC) and the University of Southern California (USC)
(Figure 6). Bathymetric data was adapted from Continental
Shelf Data Systems, San Pedro Chart 120-38-3, and is presented on Plate I.
Geophysical Surveys
California State University, Northridge (CSUN) Surveys
Field work for the author consisted of the collection of 3.5 kHz continuous high resolution data. A total of 105 line kilometers of data were collected aboard the R/V
Nautilus in October, 1979. Equipment consisted of an EDO
Western Corp. model 515 system (Table 2), with the 3.5 kHz tuned transducer mounted and towed in an Envicom "fish."
17

...
Table 1 - Seismic Data Profile Summary
3.5 kHz Uniboom Sparker Side-scan-sonar COP SOURCE
CSUN*
1973-1979
CERC**
1973
555 km
175 km
USGS***
1973
Western Geophysical
(proprietary) 1972
Dames and Moore
1978
SUBTOTALS 730 km
TOTAL 1,080 km
85 km
40 km
125 km
85 km
35 km
55 km
175 km
40
40 km km
10 km
10 km
*
**
***
California State University, Northridge
Coastal Engineering Research Center
United States Geological Survey
1-'
00

SOURCE
SYSTEM
POWER
Table 2 - Equipment Specifications
FREQUENCY
(kHz)3
PENETRATION
(meters)
CSUN*
3.5 kHz
CERC**
Acuray
2-10 kwl
1,200 j2
USGS***
Uniboom
Sparker
Dames and Moore
Uniboom
Sparker
5,000-6,000 j
120,000 j
500 j
1,000 j
Western
Geophysical
Sparker
COP
(1200% stack)
120,000 j
120,000 j
3.5
.65-3.0
.31-1.6
.5-3.0
.8-.35
2.5
* California State University, Northridge
** Coastal Engineering Research Center
*** United States Geological Survey
15-30
50
50
850
100
125-175
1000
6000
RESOLUTION
(meters)
SWEEP
0.5
0.5
1.0
15.0
0.5
5.0
1/4 sec
1/4 sec
1/4 sec
3 sec
1/4 sec
1 sec
15.0
20.0 lkw kilowatt
2j joule
3kHz - kilohertz
3 sec
5 sec
......
1.0

. 33°47'
33°40'
118000' 118°10~
LONG BEACH
SAN GABRIEL RIVER e ARMY CORPS OF ENGINEERS
• usc
• BECHTEL CORP.
0 SHELL OIL COMPANY
SAN PEDRO BAY
~.
14
•A-38
•A-16
6 V-1
AV-8
AV-14 • A-17 A V-15
•v-5
_. V-28
•v-22 eA-40 6V-9
•v-19
AV·2• V-3 e A-18 A V-13 eA-19A V-16 e A-23 6 V- 10 A-22 e -. A-21
A V-6 A V-27
A V-11
•A-24
HUNTINGTON BEACH
•A-10 A V-26
.A..V-7
""AV-12 e
A-26
• A-12 A V-30 A V-2& e A-41 e
A-27
• A-13 e
A-11
Q CH-261-1
CH-261-2
FIGURE 6 LOCATION OF ROTARY BORINGS AND VIBRATORY CORINGS ON THE SAN PEDRO SHELf l'V
0

Tow speed varied between four and five knots, and record quality was generally good to very good. Positioning on this survey was provided by precision radar fixes (range and bearing), Loran C, and, in part, by a Del Norte electronic navigation system. The accuracy of the Del Norte system is + 3 meters, and when compared to the Del Norte system, the combined Radar-Loran C systems yielded an accuracy of + 150 meters.
Surveys run between 1973 and 1977 employed the same
EDO Western system, but earlier surveys (1973-1974) utiiized a sled-mounted transducer. This factor, along with an increased boat speed of 5 to 7 knots, reduced data quality considerably. Quality ranged from poor to good on these surveys. Navigation on the earlier surveys was provided by combining triangulations from two or three shore-based alidade stations with radar ranges and bearings. An accuracy of + 30 meters was recorded when visual contact was maintained, and this was reduced to + 300 meters for positioning beyond visual range (Rudat, 1980).
Coastal Engineering Research Center (CERC) Survey (1973)
This survey was run by McClelland Engineers (formerly
Bolt, Bernack, and Newman, Inc.) for the Army Corps of
Engineers, Coastal Engineering Research Center during June of 1973. High resolution Acuray data were collected with an average grid spacing of two kilometers. Data quality varied from good to very good, with an average penetration
21

of 50 meters (Table 2) • Positioning for this survey was provided by a mini-ranger navigation system, with an accuracy•of + 10 meters.
United States Geological Survey (USGS) Survey (1973)
The USGS conducted this survey aboard the R/V George
B. Kelez in 1973 (Leg 2, Wagner, 1975). Uniboom and intermediate penetration sparker data were collected, with an average grid spacing of two kilometers. Average penetrations for the Uniboom and sparker data were 50 and 850 meters, respectively, with data quality varying from fair to good (Table 2). A Shoran navigation system provided positioning for the survey with an accuracy of + 10 meters
(Greene and others, 1975).
Dames and Moore Survey (1978)
This survey was run by Dames and Moore Consultants, under contract to Shell Oil Company in March of 1978.
Several types of data were collected~ those useful to this study were Uniboom, sparker, and side-scan sonar. The quality of the data was generally very good, and positioning for the survey was furnished by a mini-ranger navigation system (Motorola), with an accuracy of + 3 meters.
22

' 0
Data Reduction and Interpretation
In the seismic reflection method, a seismic pulse is produced by a system and is then reflected from interfaces having different physical properties (Dobrin, 1976). The most common methods of seismic pulse generation are mechanical impact, explosion, or vibration. Reflection from interfaces results from a contrast in acoustic impedance of the material. The seafloor, faulting, bedding planes, unconformities, and gas zones are examples of typical acoustic ref lectors (Sieck and Self, 1977) • Acoustic reflectors are displayed graphically on a recorder, with the records exaggerated five to fifteen times. The scale of the record depends on the ship speed and the recorder paper feed. The power and frequency of the system determine the depth of penetration and degree of resolution of the system. For a detailed discussion of the seismic reflection method and the interpretation of seismic reflection profiles, the reader is referred to Moore (1960),
Dobrin (1976), and Sieck-and Self (1977).
Depth to acoustic reflectors is a function of the sound velocity of the reflecting materials. Sound velocity can be calculated from the physical properties of the reflected unit. Hamilton (1974) determined a laboratory velocity of 1,664 meters/second for sandy-silt {5.1 phi}.
By correlating reflectors from seismic profiles to actual borehole horizons, Bechtel {1967} calculated a velocity of 1, 731 meters/second for the upper 75 meters of Pleis-
23

tocene sediment (this included both upper and lower Pleistocene deposits) off of Bolsa Chica State Beach (Figure 4).
Using this same method, Fischer and others (1977) found velocities of 1, 700 meters/ second for Holocene sediments and 1,731 meters/second upper Pleistocene sediments on the
San Pedro Shelf. As a result of these studies, the author used a velocity of 1,700 meters/second for Holocene sediments and 1, 731 meters/second for Pleistocene (upper and lower) sediments.
The survey area was mapped at a scale of 1:24,000. The following maps were produced:
Structure contour map of the top of the Upper
Pliocene (Pico Formation) Plate III
Structure contour map of the top of the lower Pleistocene (San Pedro Formation) Plate IV
Isopach map of Holocene sediments - Plate V
Geologic map of the San Pedro Shelf with Holocene overburden removed - Plate VI
24

3. STRATIGRAPHY
Introduction
As previously stated, the San Pedro margin has been divided into two separate structurally controlled sections, the Palos Verdes Uplift and the Wilmington Graben (Figure
2). This study is primarily concerned with the Wilmington
Graben and coastal area, but a stratigraphic overview of the Palos Verdes Uplift is also included. A Cenozoic correlation chart is presented (Figure 7) with three generalized stratigraphic columns: the Palos Verdes
Uplift, Wilmington Graben, and the Long Beach~Newport Beach coastal zone. Stratigraphy of the Palos Verdes Uplift is extrapolated from the onshore work of Woodring and others
( 1946) in the Palos Verdes Hills. The stratigraphy has been documented on the shelf with jet and dart core data and with seismic reflection profile data correlations
(Junger and Wagner, 1977: Nardin and Henyey, 1978: Rudat,
1980).
Stratigraphy of the coastal zone is taken from published reports of oil fields (California Division of Oil and Gas, 1961) and water wells (Poland and others, 1956:
California Department of Water Resources, 1966). Coastal units are correlated with offshore borehole data (Bechtel,
1967: Lee, 1977) and extended into the Wilmington Graben through use of seismic reflection profiles.
Units exposed in the study area range in age from lower Pleistocene through Holocene. Due to the thickness
25

YEARS
S.P.
CALIF.
BENTHIC
PALOS VERDES
UPLIFT
WILMINGTON
GRABEN
LONG BEACH TO
NEWPORT BEACH
2
3
.4 u
0
N
5
0 z
10 LU u
15
20
30
60
90
PALOS VERDES SAND w z w u
0
.....J a.. w z w u
0 /
1-
V)
....
,~~
~
/
/ w
.....J a.. f(,'-~
~~~
/
/
/
~~~
~'(,~
/
/
/ <--'~~
~'(,~<(;
. /
/
/
TERRACE AND
COASTAl SANDS
SAN PEDRO FM.
Q'(,,;tt..O
MONTEREY SH. 1-
--'
::::>
MALAGA
_.. MUDSTONE <{ ----
VALMONTE u..
DIATOMITE
V)
ALTAMIRA w
SHALE
0 w z
0
N
"v'"''t'
~
0' w
>
LPN: TO LP I
6
SAN PEDRO FM.
PICO FM.
REPETTO FM.
? - - ?
PUENTE FM.
TOPANGA
FM.
R
....
~
Q) c
Cl
0
3:
\ J c
0
....
Q)
Cl c
::I
.::::!. w z
0
N
1-
--'
:::>
<{ u..
SAN PEDRO FM.
I
PUENTE FM.
TOPANGA
V)
0
--'
<{ a..
0 w
~
<{ z z
:::>
OLIGOCENE
TO
PALEOCENE u
6
N
0
V) w
LATE CRETACEOUS
TO LATE JURASSIC
BASEMENT ROCKS
CATALINA
SCHIST
CATALINA
SCHIST
CATALIN:t..
SCHIST
FIGURE 7- CENOZOIC STRATIGRAPHIC CORRELATION CHART
26

27
Footnotes from Figure 7
1 Rudat (1980),
Woodring and others (1946)
Nardin and Henyey (1978)
Junger and Wagner (1977)
2 This study and
Rudat (1980),
Modified from Truex (1974), (Wilmington Oil Field)
Mayuga (1970), {Wilmington Oil Field)
3 This study and
Rudat (1980),
Bechtel (1967), Bolsa Island Site (Figure 2)
Poland and others (1956), Coastal Water Wells
Allen and Hazenbush (1957), Sunset Beach Oil Field
Wissler (1943)
4 Nardin and Henyey {1978)
5 Note that time scale is progressively compressed
6 Table 3 summarizes lithologies, thicknesses, and other information regarding these units.

of the Pliocene-Pleistocene section in the Wilmington
Graben, definition of units below the Pico Formation (upper
Pliocene) was not possible with the data available. A subcrop geologic map was constructed for the study area with Holocene overburden removed, using seismic reflection profiles and available borehole data. Table 3 gives a detailed description of Upper Pliocene through Holocene units mapped in the study area and their onshore correlatives.
Although redefining of temporal boundaries of Neogene epochs has been suggested as a result of recent work on planktonic foraminiferal zonation and radiometric dating
(Nardin and Henyey, 1978), the author conforms with past usage in referring to the Monterey Formation as Miocene, the Repetto Formation as Pliocene, and the Pico Formation as Pliocene in age. The onset of the Pleistocene is accepted as 2.5 million years before present (b.p.) (Boellstorff, 1978), and of the Holocene transgression as 18,000 years b.p. (Curray, 1964).
Basement Rocks
The Catalina schist forms the western basement complex of the Los Angeles Basin, including the San Pedro Shelf, and is believed to constitute the basement for the major portion of the continental borderland (Vedder and others,
1974). Exposures of this schist occur along the core of the Palos Verdes anticline (Woodring and others, 1946) and
28

Table 3
Detailed Stratigraphy of the San Pedro Shelf and Onshore Correlatives (Modified from Rudat, 1980)
Area Lithology
Thickness
(max) Source Comments Unit
Palos Verdes
Sand
Lowest terrace
San Pedro
Off Bolsa
Chica State
Beach
Coastal water wells
Marine coarse grained sand and gravel with silty sand, and silt.
Basal sandy gravel to conglomerate grading to silt, sand and gravel in varying proportions.
50
15
5 m m m
Woodring and others (1946)
Bechtel (1967)
DH101@-62m
(base)
Poland and others (1956)
Locally rests on lower Pleistocene and Miocene rocks.
Thick nonmarine sediments cap this formation and merge into the upper part of the older alluvium of L. A. basin. Correlative to units LP IV to LP
I on San Pedro shelf.
Conformable with San Pedro Fm below. Anomalous thickness suggests that this unit includes older deposits.
Also caps hills and mesas along
Newport-Inglewood zone.
Terrace & unnamed coastal deposits
Palos Verdes
(P.V.) Hills higher
Coastal
Basal sandy gravel to conglomerate grading to silt, sand and gravel in varying proportions.
Marine, cleanly washed, poorly sorted, stratified sand and gravel with some silt and rubble, nonmarine rubble, gravel, and sand cap terraces.
Silt, clay, sand, and
35 m
210 m
Woodring and others (1946),
Yerkes and others (1965)
Poland and
Up to 5 m of marine and nonmarine sediments.
30 m of
Found in Wilmington area, part of Long Beach plain, under Sunset Gap, and beneath Huntington
Beach Mesa. In Bolsa Island drill holes (Bechtel, 1967), a portion of the sediments named
Palos Verdes Sand may be correlative with these sediments.
San Pedro Fm P.v. Hills Divided into three members:
(1) San Pedro Sand cross-bedded sand with gravel silty sand and silt.
(2) Timms Pt. Silt silt and silty sand.
(3) Lomita Marl calcareous sand.
185 m
(90 m)
(85 m)
Woodring and others (1946)
Members may be
San Pedro Fm. facies in the
Nonetheless
San Pedro sand is always in upper part.
~
1.0

"'"
Unit
San Pedro
Fm
Pice Fm
Repetto Fm
Area
Off Balsa
Chica State
Coastal water wells
Off Newport
Beach
Coastal oil fields
P.V. Hills
Coastal oil fields
San Pedro basin and
Wilmington graben
Lithology
Table 3 (page 2 of 3)
Thickness
(max)
Poorly sorted, coarse sand, and gravel.
Silt, clay, sand and gravel.
270
270 m m
Source
Bechtel (1967) drill holes @
-44 to -72 m
(top)
-244 to -305 m
(base)
Poland and others (1956)
Poorly sorted coarse grained sand and gravel.
180 m Lee (1977)
Fine to coarse, occasionally pebbly, gray sand with olive gray and olive brown mostly soft, massive, claystone and siltstone.
Wilmington Wissler (1943)
360 m
Seal Beach
830 m
Huntington
Beach 400 m
Soft, massive, glauconitic foraminiferal siltstone
50 m Woodring and others ( 1946)
Alternating beds of fine to coarse, loose to compact, occasionally pebbly, poorly cemented sand and sandy silt.
Wilmington
350 m
Seal Beach
830 m
Huntington
Beach 460 m
Alternating beds of fine to coarse, loose to compact, occasionally pebbly, poorly cemented sand and sandy micaceous shales, siltstone and claystones.
1200 m
Wissler (1943)
Junger and
Wagner (1977)
Comments
Conformable with P.V. sand above.
Correlative but thicker and and more heterogeneous than on
P.v. Hills.
Strong angular unconformity at base.
Unconformably overlies Repetto Fm in Wilmington,
Sunset Beach, and Huntington Beach Oil Fields (Mayuga, 1970: Hazenbush and
Allen, 1958: Allen and
Hazenbush, 1957).
Greatly abbreviated on the hills, compared with 1,200-
1,500 m in L.A. Basin. Disconformable with underlying
Malaga Mudstone.
In Wilmington and Huntington
Beach oil fields the Repetto is conformable on the Puente
Fm (Mayuga, 1970, Allen and
Hazenbush, 1957). Conformable off west Newport Beach
(Lee, 1977). w
0

Unit
Monterey
Shale
Puente Fm
Puente Fm
Topanga Fm
Basement
Rocks
(Catalina
Schist)
Area
P.V. Hills
Coastal oil fields
Off west
Newport aeach
Coastal oil fields
Palos Verdes
Hills
Table 3 (page 3 of 3)
Lithology
Divided into three members:
Malaga Mudstone - Radiolarian mudstone
Valmonte Diatomite -
D~atom~te, diatomaceous shale, and diatomaceous mudstone.
Altamira Shale (divided into 3 sub-units). Silt sandy, cherty, porcelaneous, phosphatic, chert, and limestone.
1220 m
Organic shale, sand and schist bearing conglomerates at the base. Platy
2,000 m shales, silty sands, sandy claystones and fine to medium sands, grading to predominantly fine to coarse sands with micaceous siltstone and platy shale at the top.
Finer grained lithology than the on-land section.
830 m
Medium to coarse sandstone and dense shale.
Green to greenish-gray quartz-sericite schist, red-weathering to lavenderweathering quartz-talc schist, and blue schist with quartz and glaucophane or crossite.
300 m
?
Source
Woodring and others (1946)
Wissler (1943)
Comments
On the San Pedro shelf Junger
& Wagner (1972) estimate a thickness of 1300 m.
Present in Wilmington, Sunset Beach, and Huntington
Beach oil fields (see Pico
Fm. for sources).
Lee (1977), oil industry bore-holes,
Base @-2,000 to 2,700 m, Top
@-1,870 m
Wissler (1943)
Woodring and others (1946)
From aquapulse seismic profiles, this unit exhibits a south-westward thinning towards a basement high, and dips to the north
(Rudat, 1980).
Present in Wilmington,
Sunset Beach, and Huntington Beach oil fields (see
Pico Fm for sources).
May be correlative with
Franciscan assemblage
(Reed, 1933). w
1-'

on parts of Santa Catalina Island (Mayuga, 1968). This western basement complex is not present east of the Newport-Inglewood zone of deformation (Vedder and others,
1974).
The age of the Catalina schist is not precisely known. Exposures of this fine-grained, gray green, chlorite bearing schist show close similarity to the Franciscan schist of central California, implying a Cretaceous age
(Woodford and others, 1954). However, textural properties of the Catalina schist also resemble the pre-Cambrian
Pelona schist (Woodford and others, 1954). A K-Ar age of
95-109 million years (middle Cretaceous) has been found for the Catalina schist exposed on Santa Catalina Island (Suppe and Armstrong, 1972).
No exposures of basement rock are present in the study area or along the adjacent coastal zone. Borehole data offshore from the Santa Ana river places the basement at a depth of 2,730 meters below the seafloor (Lee, 1977, proprietary). Junger and Wagner (1977) and Rudat (1980) report local exposures of this schist southeast of Pt. Fermin on the San Pedro Shelf.
Miocene Rocks
Overlying the Catalina schist in the Palos Verdes
Hills is the Monterey Formation of upper Miocene age (Figure 7). The Monterey Formation is divided into three members: the Al timira Shale, the Valmonte Diatomite, and
32

the Malaga Mudstone (Woodring and others, 1946) . Occurrenee of the Monterey Formation on the offshore portion of the Palos Verdes uplift has been documented by dredge hauls
(Moore, 1954) and jet and dart core data (Nardin and
Henyey, 1978). Using this data along with seismic reflection profiles, Rudat (1980) mapped the Monterey Formation over most of the Palos Verdes uplift, correlating seafloor outcrops evident on seismic reflection profiles with existing boring data.
In the Wilmington Graben and along the coastal area,
Miocene rocks consist of the Topanga Formation of middle
Miocene age, and the Puente Formation of upper Miocene age
(Figure 7). As observed in coastal oil well data (California Division of Oil and Gas, 1970), the top of the upper
Miocene occurs at a depth of 1.676 meters to 792 meters below the surface along the coastal area. Borehole data offshore from the Santa Ana river places the top of the
Miocene (Puente Formation) at a depth of 1,870 meters (Lee,
1977).
Pliocene
Pliocene rocks in the Palos Verdes Hills consist of the Repetto Formation of lower Pliocene age. Although the name Repetto Formation has been abandoned by the USGS for not meeting the requirements for the definition of a formation, the nomenclature of local usage is used here to avoid confusion. The Repetto Formation consists of soft,
33

massive, glauconitic, foraminiferal siltstone, and lies disconformably on the Malaga Mudstone (Woodring and others,
1946). This formation attains a maximum thickness of 45 meters in the Palos Verdes Hills, and the upper Pliocene
(Pico Formation) is absent (Woodring and others, 1946}.
The limited section of the Repetto Formation and the absence of the Pico Formation (upper Pliocene) suggest that deformation began in the early Pliocene in the Palos Verdes
Hills and continued through late Pliocene. The strongest period of deformation occurred after the deposition of the
Repetto Formation (Woodring and others, 1946).
Both the Repetto and Pico Formations are found in the
Wilmington Graben and coastal area. These two formations have been further divided by Wissler (1943) into lower, middle, and upper subdivisions on the basis of foraminiferal assemblages. The Pico Formation lies unconformably on the Repetto Formation, and Conrey (1967} attributes this to uplift of the western margin of the Los Angeles Basin at the end of the early Pliocene. Thickness of the Pliocene in these areas ranges from several meters to several hundreds of meters. The Repetto Formation is not identified on the seismic reflection profiles of this study.
In the coastal areas, the upper division of the Pico
Formation is marine and consists mostly of sand, silt, and clay (Poland and others, 1956). The middle and lower Pico
Formation and the Repetto Formation are largely marine siltstone and shale.
34

The upper portion of the Pico Formation is identified in the Wilmington Graben with the seismic reflection data
(Figure 8). From limited borehole data offshore of the
Santa Ana River, the upper part of the Pliocene is composed primarily of yellow clay and gray silty clay with interbedded poorly sorted sands (Lee, 1977). The section of the
Pico Formation that is identified on the seismic reflection profiles displays horizontal bedding in the southwestern portion of the area. In the inshore area, i t reflects the local structure of the Wilmington anticline and the Wilmington Graben (Figure 8).
The top of the Pico Formation occurs at a depth of 575 meters below sea level on the outer shelf and at a depth of 125 meters below sea level offshore of Huntington Beach
(Plate III). Landward of this fault zone the location of the Pliocene-Pleistocene boundary is questionable due to the resolution of the geophysical data.
Pleistocene Sediments
As stated earlier, Boellstroff (1978) proposes an age of 2.5 million years b.p. for the Pliocene-Pleistocene boundary. Butzer (1974) proposed a division of the Pleistocene as follows: lower (1.8 million to 700,000 years b.p.), middle (700,000 to 130,000 years b.p.), and upper
(130,000 to 10,000 years b.p.). Butzer•s (1974) divisions between lower and middle ( 700,000 years b. p.) and upper
(130,000 years b.p.) are used in the following discussion.
35

• d
-
....
~-:-~~ _::·~··~~.::-!:~~:::.~_:.:,.::~:~~~3~::0::~::-.:~
:~-~-~~~.:~~-~.;!!'!~
~ ,._
....
~--·-
...
~~.t.:.!~..:..:....-_~.!.!.:'!:.·-~:~::.:..:.=-~o::~---·-~~~~
_,..,.. --<
--
~~~
--...
::.;
:
~~=~
~"''~>---x·
-
""'--~·'-··'·
.
.... .;·.~~·~??--;::;,~----~~~~~~=--
-
~--
-~::_$..~~~~.;:;;~-------,
... -----::" .. --=2: ~ ._..l, . :~~
~~ ~ ~
.
~- ~:0-•
::;' ..... •_-;. :·,
".':'.~···'·":
.•.. ' ... ·:, ...
/~· ~. ~\
.::- ...
~-~?:-:·.
~
•• • .: .....
~':!;· ·~
•• • .. ;: ;·
~···· .,~·· '\"'~-·•''· s::·., .-._ · . . ~~~:.:-~i:~.: ~ ~ ~~ .:.:~·~1~~-:~~-:. ~ ·)··.:,~/ :~~~~
·;·.·
·,·.~:·~:.;:~:.=:; ::·:.; :::~~~·! -~. ~ ;,\ ~~ ~-.:~:~-~~::
~ 1~
1
1
5 20 25
~
Seafloor
~~as~~~~~
----
"--.. -
~--
-
Bubble Pulse r j w
:E j::
..J
0 w
U>
~<(
::il=
::!>
:::!:<(
8~
0
~
1-
1
FIGURE 8 SPARKER LINE 445 (USGS)
36

• d
Lower Pleistocene
In the Palos Verdes Hills, the lower section of the
Pleistocene is represented by the San Pedro Formation, which lies unconformably on either the Repetto Formation or the Monterey Formation. Woodring and others (1946) assigned the San Pedro Formation to the lower Pleistocene based on faunal assemblages, and divided i t into three members in the Palos Verdes Hills: the basal Lomita Marl, the Timms Point Silt, and the San Pedro Sand. Recently,
Wehmiller and others ( 1977) dated samples from the Timms
Point Silt and the San Pedro Sand of this locality (Table
4). These authors found an age of one million (+ 200,000 years b.p.) for the Timms Point Silt, and an age of 350,000 to 450,000 years b.p. for the San Pedro Sand. These findings confirm an age assignment of lower Pleistocene to the Timms Point Silt, but assign a middle Pleistocene age to the San Pedro Sand.
Wehmiller and others (1977) also dated mollusks from the twelfth or highest tereace of the Palos Verdes Hills and obtained an age of 450,000 (+ 100,000) years b.p ••
These findings make the deposition of the upper portion of the San Pedro Sand coincident with the cutting of one or more of the high Palos Verdes Hills terraces (Wehmiller and others, 1977). Woodring and others (1946) had previously believed these upper terraces were cut during the late
Pleistocene.
Along the coastal area, the lower Pleistocene is
37

UNIT/TERRACE
Upper Pleistocene
Deposits
Table 4
Age Dates (Modified from Rudat, 1980)
ABS. AGE
(Y.B.P.)
23,300 (+2,100-1,600)
-
Upper Pleistocene
Deposits
Upper. Pleistocene
Deposits
Lowest terrace
Laguna·Beach
Newport Beach
&
32,700 (+2,000)
-
69,000 (+7,000)
-
Palos Verdes (P.V.) Sand 86,000 (+9,000)
Lowest San Pedro terrace
P.V. Sand
Lowest P.v. Hills terrace
P.v. Sand
Lowest San Pedro terrace
4th P.v. Hills terrace
91,000 (+15,000)
-
120,000-140,000
120,000-140,000
METHOD
AND SOURCE c14 wood c14
Shells
Uranium series closed system
Shells
Uranium series open system
Shells
?
Amino Acid
Saxidomus
(mollusk)
Amino Acid
Tegula, Epilucina
REFERENCE
Bechtel (1967)
DH102@ - 99'
Bechtel (1967)
DH101@ - 52'
Szabo
M1477
& Vedder (1971)
Szabo & Rosholt (1969)
1.6 km sw of M5908
Yerkes & Wentworth (1965)
Wehmiller and others
(1977) M5908 & M2074
Wehmiller and others
(1977) o18/o16
STAGE
Early stage 5
Early stage 5
Terraces higher than
4th (P.v. Hills)
Wehmiller and others
(1977)
7
San Pedro Sand
(12th-highest P.v.
Hills terrace)
12th-highest P.v.
Hills terrace
Timms Pt.
Silt
Malaga Mudstone
Altamira Shale
350,000-450,000
<.:!:.100 1000)
360,000
]..'000,000 (.±.200,000)
3,500,000
4,500,000
14,500,000
(+1,100,000)
Amino Acid
Tegula, Epilucina,
Polinices
Uranium series closed system
Amino Acid
Saxidomus, Protothaca
Chione
Fission-track
Upper and Lower
Malaga Ash
K-Ar
Portuguese Tuff
Wehmiller and others
(1977)
Szabo & Vedder (1971)
Wehmiller and others
(1977)
Boellstorf and
Steineck (1975)
Turner (1970)
9-ll w co

locally unconformable with the underlying Pliocene sediments. It is correlative with the type San Pedro Formation of the Palos Verdes Hills (Lomita Marl, Timms Point Silt, and San Pedro Sand) but i t is much thicker and more heterogeneous (Poland and others, 1956).
The sediments of early Pleistocene age were deposited in a shallow to moderate depth marine basin. They consist of clays, silts, sands, and fine to coarse gravels, derived from the erosion of the San Gabriel, San Bernadino, and Santa Ana mountains (California Department of Water
Resources, 1966). South of the NIZD the San Pedro Formation dips gently seaward. Beneath Sunset Gap the San Pedro sediments reach a thickness of 275 meters, thinning to six meters at the south end of the Newport Mesa (Poland and others, 1956).
In the study area, the Pliocene-Pleistocene boundary is locally characterized by an angular unconformity (Figures 8 and 9). Bechtel (1967) reports a conformable contact between these sediments based on borehole data located approximately 1000 meters seaward of Sunset Beach.
The San Pedro Formation is distinguished by gentle southwest-dipping beds. The dip of the beds along the inner shelf appears to be a result of local subsidence and posible structural growth. The lower Pleistocene sediments are disrupted by the northern fault zone bounding the Wilmington Graben, and this fa~lt activity is reflected by steeper dipping beds in the inshore area (Figure 10).
39

-
135 130 125 120
Seafloor
Bubble Pul•e l
~~ ~~
(,)W w>
Cllc(
:Ja:
...JI-
~>-
8~
O l
0
~
FIGURE 9
... 5000 FEET ...
SPARKER LINE 449 (USGS)
40

98 ds
90 85 or Seafloor 8
1
0
~Tp ~~
:::: ::::::::---==
~~
Bubble Pulse
[ p~~
~
- - T p
-
0 z
0
(.) w
~
..J
..J
~
..J w
>
<( a:
I-
>
<(
8
~
~
1 l
1l
I
-5000 FEET .,
FIGURE 10 SPARKER LINE 453 (USGS)
41

Borehole data seaward of Newport Beach identifies the San Pedro Formation as a poorly sorted, coarse-grained sand to gravel unit (Lee, 1977). At this location the lower Pleistocene section is 180 meters thick, increasing to approximately 225 meters in the central portion of the
Wilmington Graben.
The top of the San Pedro Formation occurs approximately 350 meters below sea level at the seaward edge of the study area (Plate IV). This contact rises to the northeast, and the San Pedro Formation is believed to crop out approximately one mile southwest of Huntington Beach, on the crest of the Huntington Beach anticline (Figure 11)
Upper Pleistocene
The sediments of upper Pleistocene age in the Palos
Verdes Hills include both marine and non-marine capping terrace deposits (Woodring and others, 1946). Deposits of middle Pleistocene age are believed to be minor or absent in this area. This is because the middle Pleistocene is recognized as a time of intense deformation associated with the Pasadenan phase of the Cascadian Orogeny (Yeats, 1976).
However, the older publications referred to in this section
(Woodring and others, 1946, and Poland and others, 1956) use the terms "upper" and "lower" in a relative sense without absolute chronological meaning. Only recently has age dating permitted an assignment of absolute age to any of the deposits discussed below, and although many of these
42

L HOLOCENE
.l ~ ~.1
FIGURE 11 UNIBOOM LINE 455 (USGS)
..,...-Seafloor
43

ages may require further refining, they are presented in this discussion.
Marine terrace deposits are found capping all thirteen
Palos Verdes Hills terrace levels. They unconformably overlie the San Pedro Formation, and this unconformity is believed to represent a nondepositional hiatus. Woodring and others (1946) assigned the formal name of the "Palos
Verdes Sand" to the marine deposits capping the first
(lowest) terrace. These marine deposits were given a formal name only because of the extensive occurrence of the first marine terrace on the Palos Verdes peninsula.
All of the marine deposits are capped with continental deposits on the terraces of the Palos Verdes Hills. The presence of both marine and continental sediments is a result of uplift of the Palos Verdes Hills throughout the late Pleistocene.
The Palos Verdes Sand at the first terrace in San
Pedro has been age dated by several authors (Table 4).
Wehmiller and others (1977) obtained an age of 120,000 to
140,000 years b.p. for the marine deposits on the first terrace, and the same age for the marine deposits on the fourth terrace in the western Palos Verdes Hills. As previously stated, these authors found the deposition of the San Pedro Sand coincident with the cutting of the twelfth and thirteenth Palos Verdes terraces. This fact, along with the latest Pleistocene age found for the fourth terrace, would assign a time frame of middle Pleistocene
44

to terrace levels five through eleven.
The marine deposits capping terrace levels five through eleven are believed to correspond to a series of
"unnamed upper Pleistocene deposits" identified in the coastal area by Poland and others {1956). As mapped by
Poland and others {1956), these deposits are present over a major part of that area. They are believed to be absent in the Seal Beach area, the central part of the Huntington
Beach Mesa, and in the southern part of the Newport Mesa.
Well log data identify these upper Pleistocene deposits as fine sand and silt with coarse sand and gravel layers
{Poland and others, 1956). The unnamed deposits are conformable with the underlying San Pedro Formation in the coastal area, and they are distinguished by a change in lithology from fine-grained deposits above to coarsegrained deposits below.
Correlatives of the Palos Verdes Sand and the nonmarine capping terrace deposits present on all thirteen terraces are also found in the coastal area. However, in this area both of these deposits are predominately of marine origin. These deposits have a cumrnulative thickness of approximately 20 meters {Poland and others, 1956). The capping terrace deposits occur almost everywhere throughout the hills and mesas of the Newport-Inglewood belt, but the correlative of the Palos Verdes Sand is believed to be absent on portions of Landing Hill, Bolsa Chica Mesa, and
Huntington Beach Mesa {Poland and others, 1956).
45

Both the unnamed upper Pleistocene deposits and the overlying marine deposits are mapped in the study area.
The overlying marine deposits found along the coastal area are represented by a series of units designated Late
Pleistocene {LP) IV, LP III, and LP II by Fischer and others (1977). These units were identified as separate seismic stratigraphic depositional sequences after Vail and
Mitchum (1977), and Fischer and others (1977) found them to be net offlapping sequences representing Pleistocene high and low stands of sea level. These authors mapped these sequences on the outer San Pedro shelf and correlated them to corehole data in that area (Figure 6 Shell Oil
Company coreholes}. Using only seismic reflection profiles, Rudat ( 1980) extended this interpretation over a large portion of the San Pedro shelf, including a portion of the study area of this report. Recently, Darrow and
Fischer ( 1983) revised the terminology of the "LP" units, changing their name to "Pl" {Pleistocene) units. The Pl designation is proposed as a more accurate terminology for the units, as the "IV" unit is believed to be middle
Pleistocene in age. The discussion that follows on these units is adopted in part from Fischer and others (1977},
Rudat (1980), and Darrow and Fischer (1983). The author has chosen to use the "LP" terminology to conform with
Rudat (1980), a major reference of this study.
46

Unnamed Deposits and LP IV
The "unnamed deposits" that correlate to those mapped onshore by Poland and others (1956) are believed to be middle to late Pleistocene in age. These deposits are found over the entire area with the exception of an area just seaward of Huntington Beach where the San Pedro
Formation is believed to crop out (Plate VI). These middle
Pleistocene deposits are conformable with the underlying
San Pedro Formation only in the inshore area northwest and southeast of Huntington Beach. In Bechtel corehole DH-101, located offshore of Bolsa Chica State Beach, they are conformable and consist of silts, sands, and gravels with a sandy gravel and conglomerate basal layer. Just offshore of Huntington Beach they appear to be unconformable as a result of continued structural activity during deposition.
Farther offshore in the Wilmington Graben, these deposits are forset and unconformable with the San Pedro Formation
(Figure 12), implying different conditions of deposition possibly associated with fault growth along the northern edge of the Wilmington Graben during the early Pleistocene.
Unit LP IV is only locally unconformable with the
"unnamed deposits". Offshore of Huntington Beach, USGS line 455 shows an unconformable contact between these two units (Figure 13). Elsewhere in the study area, this contact is not identifiable, and i t is only tentatively mapped (Plate VI). It is probable that similiar conditions existed during the deposition of both of these units and
47

'" "
4
IJ\
\l'i llS
/16
II{
~-
..
..
~
.....
,
,-.-6,
~ '
-~:· • tr
·~~· ·~.
· '
115 125
Seafloor
120
LP IV+ Op
- c - - -
FIGURE 12 SPARKER LINE 5A (DAMES
----
& MOORE).
---en w
::i: i=
0 -1 z w
0
>
<(
-1
-1 a:
!!! 1-
>
<(
:::!E:!:
0
M
I
0
~
48

8 9 10
,-seafloor
- ?
30 MILLISECONDS lWQ-WAY TRAVEL TIME
{
1000 FEET ---:oo
FIGURE 13 UNIBOOM LINE 455 (USGS)
49

• <) that they may represent the smae depositional sequence over the major portion of the survey area. They are unconformable at this location because of the influence of structural activity on the Huntington Beach anticline during their period of deposition
The unnamed deposits thin toward the south, and
Fischer and others (1977) report unit LP IV lying unconforably on the San Pedrro Formation on the outer edge of the shelf. LP IV is thin along the northeast portion of the shelf, and i t thickens to the south as i t heads towards the shelf break. Seismic reflection profile coverage was not adequate enough in the southeastern portion of the survey area to determine the relative thickness of LP IV or the exact stratigraphic relationship between i t and the unnamed deposits. The unnamed deposits are known to be absent on portions of the Newport Mesa, and their existence offshore of this area could not be verified.
LP III
The limit of occurence of unit LP III follows that of
LP IV but i t is located farther seaward (Plate VI). LP III lies unconformably on LP IV and is believed to also consist of silts, sands, and gravels. Fischer and others (1977) report three seismic stratigraphic facies within LP III on the outer shelf: Facies I, conglomerate filled channels
7
Facies II, sand filled channels7 and Facies III, silt-sand filled channels. These facies were identified based on
50

seismic character and geographic distribution of apparent gravels, however, they were not identifiable in the study area. On the outer shelf a basal gravel bed approximately two meters thick was noted on the outer shelf, but was not confirmed in the study area.
In the study area LP III has a gentle southeasterly dip which steepens as i t onlaps LP IV over the structural high offshore of Huntington Beach (Figure 14}. LP III ranges in thickness from approximately 40 meters in the
Wilmington graben to approximately eight meters at its northeastern extent where i t appears to be partially truncated by Holocene beds (Figure 14}. Where LP III is overlain by LP II, i t is slightly thinner (Figure 15}, implying erosion after deposition of LP III by a transgressive pulse at the beginning of LP II time (Rudat,
1980}.
LP II
LP II lies unconformably on LP III and has a northeastern limit that is slightly seaward of the limit of LP
III (Plate VI}. In the study area this unit is generally thin, ranging in thickness from approximately five to seventeen meters. At several locations along the northeastern limit the basal unconformity of this unit forms a terrace (Figure 15} • LP II commonly displays tightly spaced forset beds, suggesting a nearshore environment of deposition with prograding terrace deposits (Rudat,
51

48
···-'¥·.
..
~:·.·
. p:: .
• ·.·I·
\ -.,. ~
. . .
..
. . .
50
HOLOCENE
-
LP I l l - - - - -
54
,.- Seafloor
FIGURE 14
2000 FEET
ACURAY LINE A-G (CERC)
52

1~8
-
Multiple/
-
HOLOCENE\
--....
1Js
.(Seafloor Channe~)
LP II
I
. FIGURE 15
1500 FEET I
UNIBOOM LINE 4A (DAMES & MOORE)
53

1980) (Figure 15).
LP II is commonly channeled, and channels filled with sand and gravel (Fischer and others, 1977) (Figure
15). The main body of this unit is silt and clayey silt and i t appears on the seismic reflection profiles as continuous horizontal high amplitude reflections.
Holocene sediments overlie LP II in the study area.
Truncation from the Holocene transgression is shown on the seismic reflection profiles (Figure 16}. On the basin slope LP II is overlain unconformably by unit LP I, but this area was not mapped in this study. For further information on unit LP I the reader is referred to Fischer and others (1977) and Rudat (1980).
Late Pleistocene Chronology
Several workers have documented the feasibility of using the o
18
;o 16 ratios of planktonic foraminifera shells to indicate changes in water temperature, ice volume, sea levels, and worldwide climatic changes (Emiliani,
1966: Shackelton and Opdyke, 1973 and 1976). Twenty-two stages have been recognized for the Pleistocene (Figure
17). In order to develop a chronology for the Late Quaternary evolution of the San Pedro basin margin, Rudat
(1980) correlated the Holocene/LP I to LP IV units with the ol8;ol6 oxygen isotope curve. The basis of the correlation is the lower age limit of the San Pedro Sand, which was correlated with stages 9 to 11: the correlation of the
54

--
,·
55
L.
HOLOCENE
,'s
L
-
FIGURE 16
I
-
-
----
2000 FEET
----
_l
ACURAY LINE A-5 {CERC)·
----
20

LP I channeling.
Final trenching of Newport-Inglewood gaps.
Slight aggradation Newport-Inglewood gaps.
Coiling ratios of Neogloboguadrina oachiderma change-shoaling begins.
Initial trenching of Newport-Inglewood gaps.
0
CXl
-
......
-
0
0
0
~
LP I)LP
I~
LP 111)
1.0-4_?-?--?
UPPER
PLEISTOCENE da
000
YRS.
Palos Verdes (P.V.) Hills terrace.
Hi lis terrace .
-
\ Palos Verdes Sand
4th P.V. Hills terrace
1st terrace in San Pedro
MIDDLE PLEISTOCENE
San Pedro Sand
Palos Verdes HillS'
12th terrace.
700,000
YRS.
LOWER PLEISTOCENE
FIGURE 17 QUATERNARY SEA LEVEL FLUCTUATIONS AND THEIR CORRESPONDING o16;o18 STAGES
(RUDAT, 1980)
(J1
0\

• tl
Palos Verdes Sand with stage 5 (Wehmiller and others
1977): and the upper age limit which places the Holocene/LP
I unit within stages 1 and 2.
Using these boundaries, and assuming each unit was deposited during a cold/warm cycle of the curve, the following provisional time sequence was produced by Rudat
(1980). I t is recognized that non-uniform rates of sedimentation and subsidence, along with varying amounts of erosion, would result in a more complex correlation.
Unit 0 1a10
16
Stage (K
Age
Years B .P.)
1. (a) Holocene
2.
(b) LP I
LP II
3.
4.
LP III
LP IV
1
2
3-4
5-6
7-8
0-10
10-20
20-30
30-140
140-230 (?)
On the outer shelf LP IV overlies the San Pedro Sand, so LP IV is correlated with the next younger major cold/ warm cycle (stages 7 and 8). The unnamed deposits which are present on the inner shelf are believed to also correlate to these stages. LP III is correlated to stages 5 and
6, and since LP II is thinner than LP III i t correlates well with the brief cycle of stages 3 and 4 •
57

Holocene
Holocene deposits along the coastal zone consist of clay, silt, sand, and gravel, predominantly of fluvial origin. They are the latest contributions of the Los
Angeles, San Gabriel, and Santa Ana rivers. The coarse sand and gravel layers are chiefly the channel deposits of major streams that were incised at the end of the late
Pleistocene and rapidly infilled. The fine sand, silt, and clay are mostly floodplain deposits contributed during flood stages (Poland and others, 1956).
Based on general physical character and water-bearing characteristics, the Holocene deposits are divided into an upper and a lower division composed of fine and coarse grained materials, respectively. These deposits have a thickness of approximately 30 to 50 meters in the water gaps, thinning to approximately 6 meters on several of the hills and mesas (Poland and others, 1956).
Corehole data at the proposed Balsa Island site show the Holocene sediments to consist of a basal very fine to coarse grained, gray to dark gray micaceous sand and silty sand with scattered pebbly lenses, grading upward to a buff gray sand with scattered round pebbles and shell fragments
(Bechtel, 1967). Vibracore data throughout the study area show the surficial sediments ( 0 to 5 meters) to be olive gray and gray silts and sands.
An isopach map of the Holocene sediments was prepared for the study area and is presented as Plate v.
The
58

Holocene sediments range in thickness from zero meters seaward of Huntington Beach, to approximately 22 meters southeast of the Santa Ana river mouth. In the area offshore of Huntington Beach, the late Pleistocene sediments are believed to crop out as a result of continued structural growth possibly associated with the Huntington
Beach anticline, a part of the NIZD. Due to uplift associated with this structure, the Holocene sediments are presumably eroded away after deposiion by current and wave action.
To the west and southwest of this topographic high, the Holocene sediments thicken to approximately 14 meters.
On the geophysical records they appear ~~ fairly horizontal reflectors of moderate amplitude. They are distinguished throughout the study area from the underlying late Pleistocene sediments by a nearly horizontal erosional surface
(Figure 14). This erosional surface was cut during the last stage of the Wisconsian glacial and the following transgression. On the outer San Pedro shelf, benthic foraminifera of Holocene age were reported in logs from coreholes 261-1 and 262-2 (Fischer and others, 1977).
Southeast of the topographic high, in the vicinity of the Santa Ana river mouth, the sediments thicken rapidly to a maximum of 22 meters. South and southeast of this area, along the shelf edge of the Newport canyon, the thickness of the Holocene sediments thins rapidly from 22 meters to 2 meters (Figure 18).
59

--~~-
.
'
.
.('
,.:.~ :.-'-~-~·-· : .. "f''.:_c_.
'-
' If::~-~~~~-·'·~· ~.j
___ ·_
···---~·-:-~·-L-:-!........:.: -~-·
60
5 8
FEET
FIGURE 18 ACURAY LINE A-4 (CERC)

The Holocene sediments appear as a southeasterly prograding wedge onlapping the late Pleistocene sediments
(figure 18). The major source of these sediments are the
Santa Ana River (the landward expression of the Newport canyon) and the Orange County sewage outfall. Changes in location of the Santa And River mouth in the past 100 years have caused the point of longshore drift convergence and sand concentration to move approximately one kilometer northwest of the present canyon head (Felix and Gorsline,
1971). Sedimentary distributions on the shelf suggest that the Newport canyon has shifted laterally several times during the Holocene and late Pleistocene as a result of the changing point of sand input to the system (Felix and
Gorsline, 1971).
61

4 • STRUCTURE
In accordance with the structural style of the Peninsular Range Province, faulting in the study area is characterized by a northwest-southeast trend. No folding was observed in the Quaternary deposits of the study area, although the presence of the Huntington Beach anticline has a direct effect on sedimentation patterns of the Quaternary
This section discusses faults mapped in this sediments. study.
A structure contour map of the top of the Pico Formation (upper Pliocene) is presented as Plate III. A structure contour map of the top of the San Pedro Formation
(lower Pleistocene) is presented as Plate IV. Plate VI is a geologic map of the area with the Holocene overburden removed.
Faulting
Several major and minor faults were mapped in the survey area (Plate VI). The major faults are designated by the letters A through E, and minor faults are referred to by their proximity to the major faults.
The major faults mapped represent the mainland boundary of the Wilmington Graben, and they correspond to the faults mapped previously by Junger and Wagner (1977).
These faults separate the horizontal sediments of the graben from steeper-dipping sediments associated with a structural high. Due to the line spacing of the geophy-
62

. ' sical data, the faults are presented as a discontinuous series, although they may well form a more continuous fault zone (as depicted on Figure 2).
Fault A is located approximately 6.0 kilometers seaward of Bolsa Chica State Beach and trends northwestsoutheast with an approximate length of 3.4 kilometers. On the geophysical records this fault is characterized by approximately 20 meters of vertical separation in the lower
Pleistocene sediments (Figure 10). Fault A is not mapped as disrupting any sediments younger than lower Pleistocene.
Fault B, located 3.7 kilometers offshore of Huntington
Beach, trends approximately east-west for a distance of 2.6 kilometers. This fault also disrupts lower Pleistocene deposits, but the vertical separation is only approximately
10 meters (Figure 19). Horizontal separation could not be determined for either faults A or B.
Several smaller fault traces associated with faults A and B were mapped in the study area (Plate VII). The trend of these fault breaks could not be determined due to the line spacing of the data, but they are approximately the same age, and they are believed to also be associated with the subsidence of the Wilmington Graben.
Faults C and D both have the same seismic characteristics as faults A and B, but these faults do not disrupt sediments above the upper Pliocene (Plate VI). Fault c is located 3.1 kilometers seaward of the Santa Ana River mouth, and i t trends east-west with an approximate length
63

A o-.
• LP II HOLOCENE
,,,,,,,~
400,
800
1200
--:---_
~
?
I
-1
~
~
~~
~ ~
1
-----
---
·~I ~~
~
...............
-
~
1w w u.
~
:I:.
1-
0.. w
0
I I ~I l
~~
asp
LP Ill
.......
' '
-
Tp
\..
-
_SEAFLOOR r-0
A'
l-400
\.. ..
,
1800
11200
11600
I
2000 2000
2400
2400
VERTICAL EXAGGERATION 5:1
CROSS SECTION A-A'
FIGURE 19
64

' 0 of 2.1 kilometers. Located 1.4 kilometers seaward of
Newport Beach, fault D is approximately 5.0 kilometers in length and also trends east-west. Fault D has been questionably connected to fault E, located 2.3 kilometers seaward of the Newport Beach channel mouth. Fault E trends approximately northwest-southeast for a distance of 1.4 kilometers (Figure 20}.
Landward of faults D and E the seismic reflectors have a wavy discontinuous character (Figure 20}, much more chaotic than that found landward of faults A and B (Figure
10}. This is believed to be related to the onshore wrenching-style of deformation associated with the NIZD.
An attempt was made to correlate faults mapped in this study to those mapped by Morton (1973} in the vicinity of the NIZD. Morton (1973} mapped the main trace of the NIZD and two fault splays as extending offshore into the survey area (Plate VI}. The main trace is mapped extending offshore in the vicinity of the Newport pier, and this trace is reported as portraying Holocene movement. One fault splay is mapped heading offshore just west of the
Santa Ana river mouth, with reported Pleistocene movement, and a second splay is mapped off of the Huntington Beach pier, also with Pleistocene movement. Faults mapped in this study in the vicinity of the Huntington-Newport Beach area include: one fault located northeast of fault C with an tentative age of late Pleistocene, two faults located landward of fault D, with ages of early and late Pleisto-
65

0.
0.5. u;
0
~
~
:X
~ w
0
1.0.
•
LOCATION
65 41
•
......
, 7 sw
0
SCALE
2 KM
NE
66
FIGURE 20 AOUAPULSE LINE SW 8 (LEE, 1977)

cene, and one fault located northeast of the Balboa pier, with an age of late Pleistocene (Plate VI).
No direct correlation could be made with the faults mapped by Morton (1973). Poor data quality in the nearshore area offshore of Huntington Beach prohibited any good correlation with the two splay faults, although one single fault break, with an age of early Pleistocene, was mapped approximately 610 meters off of the Santa River mouth.
Fault E (Figure 20), offshore of the Balboa pier, could correspond to the offshore extension of the main trace of the NIZD, with navigational inaccuracy accounting for part of the discrepency. However, this fault does not exhibit any breaks in the Holocen-e sediment. Guptill and Heath
( 1981) have found evidence of Holocene (surface) displacement along the main trace of the NI ZD in the vicinity of
Newport Mesa, approximately 3. 2 kilometers northwest of where the fault is projected offshore.
Farther northwest, directly offshore of Huntington
Beach, several smaller faults are mapped trending northeast-southwest, opposite the structural trend of the area.
These faults disrupt upper Pleistocene sediments (Figure
21). and i t is possible that these faults also have a horizontal displacement component. These faults are believed to be associated with continued growth of the
Huntington Beach anticline.
67

-1
-; i
I
·---·-··-·---
I l---
-----1-.
--·-
68
HOLOCENE
;::;Z Op
- - - -
GAS
Seafloor
J r
~
Op
I
2000FEET
I
FIGURE 21 ACURAY LINE A-G (CERC)

5. NEOGENE EVOLUTION OF THE INNER SAN PEDRO SHELF
This section discusses the structural evolution of the San Pedro shelf and the surrounding coastal area. An overview of the origin of the continental borderland is followed by a detailed discussion of the Quaternary events responsible for the present-day configuration of the Los
Angeles Basin, the Palos Verdes Hills, and the San Pedro
Shelf.
The California Continental Borderland consists of a series of basins and ridges created largely by faulting.
The origin of the borderland is problematic because an offshore block with a sedimentary sequence of Cretaceous and Paleogene rocks is separated from a mainland sequence of the same age by a metamorphic terrane of Catalina Schist
(Yeats, 1979). Researchers in the area disagree as to whether the middle Miocene structrual style, which was responsible for creating this enigma, was of a strike-slip or of an extensional nature. Howell and others (1974,
1975) advocated the strike-slip hypothesis, proposing 120 to 160 kilometers of oblique right-slip along an East Santa
Cruz Basin fault (ESCB) separating the offshore block from the mainland. In several of his earlier papers, Yeats
(1968,1973, and 1976) advocated an extensional regime during middle Miocene time, and suggested rifting of the offshore block away from the mainland.
Recent work north and south of the Channel Islands by
69

' i1
Junger {1979) found no evidence of the ESCB fault. All of the northwest-trending strike-slip lineaments reported are late Miocene or younger in age. At the time Howell and others {1974) proposed this fault, it was still believed that the San Andreas fault was also undergoing strike-slip movement during this time. It has since been determined that all of the displacement along the San Andreas fault has occurred within the last 12 million years {Crowell,
1975).
Recent paleomagnetic studies of Neogene igneous rocks of southern California have added insight to this problem.
Kamerling and Luyendyk {1979) and Luyendyk and others
(1980) have found crustal units of Miocene rocks from the
Santa Monica Mountains and Anacapa Island with apparent clockwise rotations of approximately 70 to 80 degrees.
They proposed that these rotated crustal units were small lithospheric plates that were separated from the North
American plate in the right-lateral shear couple between the North American and Pacific plates. This model is presented as Figure 22. These authors believe that the rotations began in late Oligocene time { 29 million years b.p.) at the earliest, during the initial contact of the
North American and Pacific plates. The rotations probably ended in late Miocene time when the San Andreas fault broke through southern California {Kamerling and Luyendyk, 1979).
The east to west shift to different surfaces of weakness caused local extension and compression within the broad
70

-··
' en w
(.!) z
<(
0::
1en
<(
0
(.JI 1 I 1/
' J
.,,_
.....
-.,
/ A Y /
,,
_,._,
·-
0 IOOkm apprax.
I
0::
<(
..J
:::l en
.z z w
(L
3-A
A rotation model for southern California tectonic history. Faults used in the model are: Coast Ranges west from San
Andreas = Cuyama, Rinconada, Nacimiento, Hosgri, and Santa
Lucia Bank. Peninsula Ranges west from San Andreas = San
Jacinto, Elsinore, Newport-Inglewood, and East Santa Cruz-San
Clemente. Transverse Ranges = Big Pine-Pinto Mountain, Santa
Ynez-Biuc Cur, Simi(?)-Hayfield, and Malibu Coast-Santa Moni-
0 ca-Salton Creek. In the Mojave region, the rotated block is bounded by the Garlock, Calico, and Manix-Cady faults. A. Inand unrotatcd blocks. C. Late Miocene rime geometry showing the ferred initial fracture pattern and prerotation geometry for through-cutting of the Transverse Ranges by San Andreas, San
Oligocene time in southern California. B. Miocene-Pliocene time Gabriel, and Elsinore faults, and the jump of the San Andreas fault
(?) geometry after the clockwise rotation event which probably occast to the San Jacinto. Basins are shown filled. D. Present geometry curred in mainly Miocene time. Sinistral and dextral slip has ocshowing offset of the Transverse Ranges along the San Andreas curred and deltoid basins have opened at the joins of the rotated fault. Miocene basins are not shown here.
I I
0 IOOkm opprox.
Taken from Luyendyk and others (1980), Geol. Soc. Amer. Bull., Part 1, v. 91, P- 214-215
3-C ci'
0:: ::0
)> z
G>
ITI
(/)
(I)
"
>
" ..
~
;!I
~
/
/~
A ROTATIONAL MODEL FOR
SOUTHERN CALl FORNI A
TECTONIC HISTORY
( Luyendyk and others , 1900)
FIGURE 22 f
71

' I shear zone. This model would allow for the proposed ESCB fault of Howell and others (1974). Yeats (1979) acknowledges that his earlier model of pure extension (Yeats,
1976) requires modification in light of the new evidence of rotation.
The model presented by Luyendyk and others (1980) also accounts for the presence of offshore and onshore basins in
California. Triangular basins such as the Los Angeles,
Santa Maria and Santa Cruz basins would have opened at the joining of the rotated and unrotated blocks, as the blocks rotated clockwise. In an earlier paper, Blake and others
(1978) also related the formation of the basins to the plate tectonic evolution of the San Andreas fault system.
They stated that the development of the basins was related to tectonic interaction of the North American and Pacific plates and to changes in azimuth of relative shear between the two plates. The Neogene basins in southern California began to develop in late Oligocene to early Miocene time, due to their proximity to the area where the plates first made contact 29 million.years b.p •• The Neogene basins in northern and central California developed approximately 10 million.years.b.p. in response to a change in azimuth of relative shear from a more northerly to a more westerly direction. This change took place between 21 and 4.5 million.years.b.p. and resulted in extensional strain, thus creating the conditions required for basin formation.
72

' 0
Pre-basin strata of the present day Los Angeles Basin were deposited in a shallow marine or non-marine environment during three cycles of marine transgression and regression (Yerkes and others, 1965). The inception of the basin in late Miocene time was characterized by a period of thick sedimentation and volcanism, which was followed by deformation and erosion of the north portion of the basin in the late Miocene (Crowell, 1974). This deformation resulted in a phase of accelerated subsidence and deposition in the late Miocene which continued into the early
Pleistocene.
The initiation of late Miocene deformation along the
NIZD is believed to coincide with the start of the domination of. San Andreas wrench faulting in southern California.
During the late Miocene, regional stresses in the NIZD were expressed as relatively short normal faults with northwest to northerly trends. These short faults are known to displace Miocene strata along the entire zone. Several of the faults displace lower Pliocene formations in some of the oil fields along the NIZD, but they generally do not disrupt upper Pliocene or Pleistocene formations.
The existing pattern of the NIZD developed in the Los
Angeles Basin throughout the Pliocene with continuing sedimentation and right-lateral shearing (Harding, 1973).
The stress fields that had produced the normal faults along the NIZD were overriden by the right-lateral shear system, and the normal faults became inactive (Yeats,
73

' d
1973). Most of the strain of the system was being relieved along the NIZD by Pleistocene time, resulting in two relatively rigid blocks moving past one another along a zone of active faulting. The fault zone mapped in this study,
Faults A, B, C, and D, do not exhibit any deformation above the lower Pleistocene. It is believed that these faults became inactive with the onset of right-lateral shear system. Also, a decrease in sedimentation rates in the
Pleistocene affected subsidence in the graben, thus contributing to the death of the faults.
The Palos Verdes Hills fault is believed to have originated in late Miocene or early Pliocene time as a transcurrent fault with dominant right-lateral separation
(Dames and Moore, 1977). In late Pliocene or early Pleistocene time, the Palos Verdes hills were uplifted by reverse movement along the Palos Verdes Hills fault, possibly accompanied by overthrusting on the Redondo Canyon fault. During this period, the area south of San Pedro was probably still dominated by strike-slip separation, with that pattern of movement continuing into the present. The
Palos Verdes uplift acted as a barrier to sedimentation throughout the Pliocene, and i t was during the middle
Pliocene that the uplift experienced its most intense period of deformation of the Neogene rocks. Subaerial exposure of the uplift was followed by partial resubmergence, evidenced by the abbreviated Pliocene and lower
Pleistocene section on the Palos Verdes uplift.
74

In early Pleistocene time, after the filling of the
Los Angeles Basin, the deposits of the lower San Pedro
Formation began to prograde to the southwest and southeast in the Wilmington GRaben. The ancient shoreline is believed to have oscillated across the present-day Downey plain, with sediments supplied by the Los Angeles and San
Gabriel rivers (Poland and others, 1956). Subsidence was probably already occuring in the graben, evidenced by the thickness of the San Pedro Formation in the offshore area.
During this period, the Palos Verdes Hills were an island, and they did not contribute much to local sedimentation
(Poland and others, 1956).
By middle Pleistocene time the Pasadenan phase of the
Cascadian Orogeny had begun, accompanied by local uplift and the cutting of the twelfth (highest) Palos Verdes Hills terrace (Woodring and others, 1946) • This phase is believed to have continued through the middle Pleistocene at a constant rate, subsequently forming terrace levels eleven through five in the Palos Verdes Hills. The San Pedro Sand was deposited in the time period. between 500,000 and
300,000 years b.p. in the Palos Verdes Hills, and this period has been correlated to oxygen isotope stages 11 to 7
(Wehmiller and others, 1977; Rudat, 1980).
The Pasadenan phase of the Cascadian Orogeny is recognized along the coastal a~ea by the presence of local unconformities, associated with initial deformation on the
NIZD. The Wilmington Graben was probably subsiding at this
75

time, and the shoreline on the shelf was located close to the present-day location of the Palos Verdes fault (Rudat,
1980). Deposition of the unnamed deposits mapped in the study area is believed to have begun in middle Pleistocene, and unit LP IV was deposited during a transgressive-regressive glacioeustatic cycle associated with oxygen isotope stages 8 and 7, between 230,000 and 140,000 years b.p.
(Rudat, 1980). Stage 6 is recognized by a lowering of sea level, with the shoreline probably surrounding the
Palos Verdes Hills. During this time unit LP IV experienced a period of channelization on the shelf.
The late Pleistocene and Holocene periods are correlated to oxygen isotope stages 5 through 1 (Figure 17).
The beginning of the late Pleistocene was marked by submergence of the Palos Verdes and Los Angeles coastal area and the deposition of the Palos Verdes Sand (Poland and others, 1956). At this time, sea level is believed to have been approximately six meters higher than the present day, and this high is correlated to oxygen isotope stage 5
(Figure 17) (Rudat, 1980). The Palos Verdes Sand was deposited during the stage 5 high stand of sea level, and during the following general regression of stages 4 and 3.
In the Wilmington Graben Rudat (1980) has tentatively correlated the base of unit LP III with surface cut by the stage 5 transgresion. Also, the third and s1~cond Palos
Verdes terrace levels may have been cut at this stage.
Rudat (1980) found the sporadic lowering of sea level
76

associated with stages 5 through 3 to have yielded three stages of trenching. The present-day gaps of the coastal area were formed at this time, and most of the deformation of the NIZD was completed prior to the second stage of trenching. The Palos Verdes fault is believed to have experienced its greatest late-Quaternary activity at this time, while the Wilmington Graben continued subsiding.
During the stage 4 low-stand, unit LP III was being eroded and unit LP II was beginning to accumulate at a paleo-shelf break, in close proximity to the presentday shelf break. A transgressive pulse on the shelf created stage 3, and this advance cut the basal LP II unconformity and established a shoreline near the shoreward edge of the Wilmington Graben (Rudat, 1980). Activity along the Palos Verdes fault during the depostion of unit
LP II is evidenced by truncation of this unit along the fault. LP II is not believed to have extended much farther than its present mapped limits (Plate VI).
The lowest late Pleistocene, 11 Wisconsian
II I level is correlated to oxygen isotope stage 2 (Figure 17). Deformation along the NIZD and final trenching of the coastal gaps occured at this time. This low-stand ended between 13,000 and 11,000 years b.p., and the following transgression cut the basal Holocene unconformity and deposited a basal sand.
As sea level rose, finer Holocene sediments accumulated
(Plate V).
77

As previously mentioned, the NIZD has been identified as an example of wrench-stlye faulting (Harding, 1973).
Most of the observed deformation is consistent with the fault model of Moody and Hill (1956), wherin second-and third-order faults may form adjacent to the main lateral fault. The NIZD displays several types of evidence, both structural and sedimentary, that identify it as a wrench fault system; 1) laterally offset fold axes and fold flanks; 2) horizontal slickenslides in well cores; 3) offset similar stratigraphic facies relationships and juxtaposed dissimilar facies; 4) highly variable nature of the zone of deformation ; 5) en echelon fold and fault pat terns; 6) indicated strike-slip genesis of secondary associated structures; 7) parallelism of the zone with other documented wrench faults; and 8) clay-cake model studies (Harding, 1973; Woodward-Clyde Consultants, 1979).
Right-lateral displacement of 914 to 1524 meters has been measured on the lower Pliocene surface of the NIZD. A vertical displacement of 122 meters has been measured on the basement surface, 305 meters in the Pliocene strata, and 61 meters at the base of the Pleistocene (Yerkes and others, 1965). Recent movement is indicated by arching and erosion of marine upper Pleistocene and younger non-marine strata in the hills of the zone, and also documented by seismicity (Figure 5) (Yerkes and others, 1965; Teng and
Henyey, 1975). Guptill and Heath (1981) have also reported positive evidence of Holocene activity on the north branch
78

of the NIZD on Newport Mesa. These authors believe this break to be evidence of the 1933 Long Beach earthquake.
Fault E, identified in the study area, is believed to represent an offshore extension of the NIZD (Figure 20).
This fault marks a boundary between the flat lying sediments of the shelf and a series of discontinous chaotic reflectors. The minor fault located just east of Fault
E is believed to also represent an extension of the NIZD.
This fault was identified on high resolution profiles, and is mapped disrupting upper Pleistocene sediments and possibly Recent sediments. Deep-penetration geophysical profile data was not available in the vicinity of this fault to identify i t as a major structural feature.
Other evidence for recent movement on the NIZD is the continued structural growth of the Huntington Beach anticline. As shown on Plate VI, the landward limit of deposition of units LP IV and Qp was controlled by this structure. It is possible that either the sediments were originally deposited and later uplifted and eroded, or that they were never deposited on the crest of the anticline. A steepening of the seafloor slope is evident on Figure 14, where the LP units onlap the structure. Holocene sediments are also absent over a portion of this topographic high
(Plate V). Shallow gas and several minor faults trending northeast-southwest were mapped on the southern flank of the anticline. The faults are also interpreted to be a result of the structural activity.
79

' 0
6. SUMMARY
As a southwestern extension of the Los Angeles Basin the San Pedro Shelf has been active tectonically since the inception of the basin in middle Miocene time. The shelf consists of two major structural features, the Palos Verdes uplift and the Wilmington Graben. In late Pliocene or early Pleistocene time, the Palos Verdes Hills were uplifted by reverse movement along the Palos Verdes Hills fault. The Palos Verdes Hills fault is believed to have originated in late Miocene or early Pliocene time as a transcurrent fault with dominant right-lateral separation and minor vertical separation. The Wilmington Graben is a down-dropped block containing a thick sequence of upper
Pliocene and Quaternary sediments. It is bounded to the south by the Palos Verdes fault and to the north by a series of discontinuous faults and the shoreline.
The Catalina schist forms the basement complex of the San Pedro Shelf and of a major portion of the continental borderland, however this western basement complex is not present east of the Newport Inglewood zone of Deformation. Overlying the Catalina Schist in the Wilmington
Graben is the Topanga Formation of middle Miocene age, and the Puente Formation of upper Miocene age. Neither the basement complex or the Miocene rocks were identified in the study area on seismic reflection profiles due to the thick section of Pliocene and Quaternary sediments.
Pliocene deposits of the Wilmington Graben consist
80

' tl of the Repetto Formation of lower Pliocene age and the Pico
Formation of upper Pliocene age. The Pico Formation lies unconformably on the Repetto formation, and the thickness of the Pliocene section in the graben reaches several hundreds of meters. The top of the Pico Formation occurs at a depth of 575 meters below sea level in the outer shelf and at a depth of 125 meters below sea level in the vicinity of the Huntington Beach anticline.
The Pliocene-Pleistocene boundary is locally characterized by an angular unconformity in the study area. The
San Pedro Formation of lower Pleistocene age overlies the
Pico Formation and is distinguished on the geophysical profiles by gently southwest-dipping beds. The dip of the beds is interpreted to be a combined result of faulting and subsidence. The top of the San Pedro Formation occurs at a depth of 350 meters below sea level in the axis of the graben, rising to the northeast, where i t is believed to crop out close to the crest of the Huntington Beach anticline.
Deposits of middle and upper Pleistocene age in the study area consist of the "unnamed depostis" of Poland and others (1956), and the LP units of Fischer and others
{1977). These units are identified as seismic stratigraphic depositional offlapping sequences representing Pleistocene high and low stands of sea level. Units LP IV, III, and II offlap sequentially, with LP IV extending closest to shore. The LP units are disrupted by the presence of the
81

Huntington Beach anticline, located offshore of Huntington
Beach. It is possible that the units were deposited on the structure and later eroded, or that they never extended on to the uplift.
A tentative correlation between the LP and Holocene units and the oxygen isotope curve of Shackelton and Opdyke
(1973) was made by Rudat (1980). Shackelton and Opdyke
(1973) have reported twenty-two stages for the Pleistocene.
Assuming that each unit was deposited during a warm/cold cycle, and using boundary constraints given by Wehmiller and others (1977), Rudat (1980) produced a provisional time sequence for the deposition of the upper Pleistocene and Holocene units.
The majority of faulting mapped in the study area follows the typical structural trend of the Peninsular
Ranges, being northwest-southeast. Faults are mapped corresponding to the fault zone mapped by Junger and Wagner
( 1977), and these faults do not disrupt deposits younger than early Pleistocene. Two faults are mapped that are interpreted to correlate to an offshore extension of the
NIZD in the vicinity of the Balboa Pier. One of these faults shows late Pleistocene and possibly Holocene movement and a possible Holocene disturbance.
Several smaller faults showing late Pleistocene movement are mapped along the southern flank of the Huntington Beach anticline. The depositional pattern of the upper Pleistocene units in conjunction with active(?)
82

faulting are evidence for the continued growth of this structure.
In conclusion, the "unnamed" fault zone of Junger and
Wagner (1977) has not been active beyond early Pleistocene time. As viewed from the south, the faults of this zone step left, suggestive of wrench faulting, however, only vertical deparation could be demonstrated. These faults may be an older southwestern extension of the NIZD, or i t is possible that they form a completely separate zone, which was cut off to the south by the offshore extension of the NIZD.
Also, evidence for continued growth of the Huntington
Beach anticline has been identified on the shelf. Recent
(?) east-west trending shallow faults on the southern flank of the anticline along with a thinning or absence of the upper Pleistocene and Holocene units around the structure are suggestive of growth. I t has not been determined whether or not the Upper Pleistocene units were originally deposited and later eroded with subsequent uplift of the structure, or that they were never deposited on the crest of the structure due to continued growth throughout the late Pleistocene.
83

7. References
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84

Butzer, K. w., 1974, Geological and tives on the middle Pleistocene: p. 136-148. ecological perspec-
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·~~
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------, 1960, The Sea off Southern California: a modern habitat of petroleum: New York, John Wiley and Sons,
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~-Fischer,
~.
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85

1 Fischer, P. F., Simila, G., and Patterson, R. H., 1984, The evolution and activity of the Palos Verdes Fault Zone:
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1
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-----, 1975, Possible Strike-Slip Faulting in the Southern
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86

• f) f
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M. J .
I
Amer.
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Moore, D. G., 1954, Submarine Geology of San Pedro Shelf:
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