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California. Division of Mines
and Geology, Bulletin.

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24
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no. 200

OLOGY OF THE $,
.METROPOLITAN AREA
CALIFORNIA

Del Mar, La JoUa, Point Loma,

La Mesa, Poway, and SWV4 Escondido

7V2 minute quadrangles

THE LIBRARY

THE UNIVERSITY

OF CALIFORNIA

DAVIS

o GEOLOGY OF THE

SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Prepared in cooperation witli the City of San Diego

SECTION A

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

SECTION B

EASTERN SAN DIEGO METROPOLITAN AREA

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

BULLETIN 200
1975

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

UCD LIBRARY

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STATE OF CALIFORNIA

EDMUND G. BROWN JR., GOVERNOR

THE RESOURCES AGENCY

CLAIRE T. DEDRICK, SECRETARY FOR RESOURCES

DEPARTMENT OF CONSERVATION

LEWIS A. MORAN, DIRECTOR

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

\f n f

III «

(^ »

CONTENTS

SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA

ABSTRACT 9

INTRODUCTION 11

GEOLOGIC SETTING 13

PRE-EOCENE DEPOSITS 14

Santiago Peak Volcanlcs 14

Gabbro of the Southern California Bathollth 14

Rosario Group 15

Lusardi Formation 15

Point Loma Formation 15

Cabrillo Formation 15

EOCENE DEPOSITS 15

La Jolla Group 15

Mount Soledad Formation 16

Delmar Formation 16

Torrey Sandstone 16

Ardath Shale 18

Scripps Formation 18

Friars Formation 18

Poway Group 19

Stadium Conglomerate 19

Mission Valley Formation 19

Pomerado Conglomerate 19

FACIES RELATIONSHIPS OF THE EOCENE ROCKS 20

EOCENE BIOSTRATIGRAPHY 20

POST-EOCENE DEPOSITS 29

IVIiocene 29

Andesite Dike 29

Pliocene and Pleistocene 29

San Diego Formation 29

Lindavista Formation 29

Bay Point Formation 29

Pleistocene and Holocene Surficial Deposits 30

Stream-Terrace Deposits 30

Landslide Deposits 30

Alluvium and Slope Wash 35

Beach Deposits 35

Artificially Compacted Fill 35

STRUCTURE AND SEISMIC HISTORY 35

REFERENCES CITED 38

SECTION B - EASTERN SAN DIEGO METROPOUTAN AREA

ABSTRACT 43

INTRODUCTION 45

PRE-EOCENE DEPOSITS 45

Basement Complex 45

Santiago Peak Volcanics 45

Plutonic Rocks of the Southern California Bathoiith 47

Rosario Group 47

Lusardi Formation 47

EOCENE DEPOSITS 47

La Jolla Group 47

Friars Formation 48

Poway Group 48

Stadium Conglomerate 48

Mission Valley Formation 49

Pomerado Conglomerate 49

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POST-EOCENE DEPOSITS 49

Pliocene and Pleistocene Rocks 49

San Diego Formation 49

Llndavista Formation 50

Pleistocene and Holocene Surflclal Deposits 50

Stream- Terrace Deposits 50

Landslide Deposits 50

Alluvium and Slope Wash 51

STRUCTURE AND SEISMIC HISTORY 51

MINERAL RESOURCES 53

REFERENCES CITED 56

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ILLUSTRATIONS

SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA

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

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

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

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

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

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

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

undercutting and incompetent rock, looking southeast 30

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

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

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

Rosario Group on Point Peninsula, looking west 31

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

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

looking east 35

Figure 1, Index map 12

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

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

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

Diego coastal area 17

Figure 5. Model of transgressive and regressive deposition 21

Figure 6. Relationship of biostratigraphy to lithostratigraphy 23

Figure 7. Index map of fossil mollusk localities 24

Figure 8. Index map of fossil calcareous nannoplankton localities 25

Figure 9. Index map of fossil mammal localities 26

Table 1 . Clay mineral analyses 32

SECTION B- EASTERN SAN DIEGO METROPOLITAN AREA

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

Plate 2B. Geology of the Poway quadrangle In pocket

Plate 38. Geology of the La Mesa quadrangle In pocket

Figure 1 , Location map 46

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

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

and modern erosion surface 48

Table 1 . Atterberg limits and particle size distribution 52

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

quadrangles 54

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SECTION A

Del Mar, La Jolla,

and Point Loma

quadrangles

ABSTRACT

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

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

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

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

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

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

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

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

(9)

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

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

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

(10)

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

GEOLOGY OF THE WESTERN SAN DIEGO METROPOLITAN

AREA, CALIFORNIA

Del Mar, La Jolla, and Point Loma quadrangles

by Michael P. Kennedy"!

INTRODUCTION

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

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

'Geologist, Californij

1 of Mines and Geology

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

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

(11)

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

^ y<> LAKE HODGES

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

WOODSON MOUNTAIN

POWAY

QUADRANGLE
-^ (Plate 2B)

QUADRANGLE
(Plate 3B)

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

C»

COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN

Qbp I '^''P- S°y Point Formation

Qin ■•••• I Qln, Lindovisto Formation

Tsd, Son Diego Formation

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

Tf, Friars Formation

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

Formation
Kcss, Cabrillo Formation

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

Kg, Granitic rocks of the
southern California
bathollth

Figure 2 Columnar section of the San Diego continental
margin.

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

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

GEOLOGIC SETTING

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

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

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

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

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

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

I^S^xl Rocks of the southern California batholith

IW;V/| Rocks of the Santiago Peak Volcanics

Sub-La Jolla
Present day unconformity
topography

Sub-Rosario
unconformity

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

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

PRE-EOCENE DEPOSITS

Santiago Peak Volcanics

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

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

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

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

Gabbro of the
Southern California Batholith

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Rosario Group

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

Lusardi Formation

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

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

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

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

Point Loma Formation

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

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

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

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

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

Cabrilio Formation

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

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

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

EOCENE DEPOSITS
La Jolla Group

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

Mount Soledad Formation

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

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

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

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

Delmar Formation

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

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

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

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

Torrey Sandstone

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Cretaceous

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CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

Ardath Shale

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

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

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

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

Scripps Formation

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

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

Friars Formation

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

Poway Group

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

Stadium Conglomerate

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

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

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

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

Mission Valley Formation

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

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

Pomerado Conglomerate

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

FACIES RELATIONSHIPS OF
THE EOCENE ROCKS

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

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

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

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

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

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

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

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

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Basement rock

E^^

^ss^

i:^^

4 KILOMETERS'

Fluviotile-
nonmarine deposits

Lagoonal Beach and neorshore Deep marine

deposits marme deposits deposits

300-1
200-

METERS'

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

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

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

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

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

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

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

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

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

EOCENE BIOSTRATIGRAPHY

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

GEOLOGIC
COLUMN

STAGE OR AGE

STRATIGRAPHIC SEQUENCE, FACIES RELATIONSHIP,
AND COMPOSITE FOSSIL LOCALITIES

ABSOLUTE AGE

(RADIOMETRIC)

IN MILLIONS

OF YEARS

I
o

Q-
UJ

z
< en

UJ UJ
O- o

IT t-
3«
Ul

3 =

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U. UJ

tins

UJ< cc

NORTH

AMERICAN

MAMMAL

AGES

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

42 —

43 —

44 —

45 —
45 —

47 —

48 —

49 —

50 —

LJ
<_>

LlI

<
_l

Z
<

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a:

z
o

»-

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E
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3

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

VALLEY V4 ^^>-

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

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

a.
o

o
a.

z
o
l-
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^...^^ ^^^"^Ms^^^^^^-E^i!!!^

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

^\„^^^T10N ^^^^ORMATION

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

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

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

Q
Q

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

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

UJ
(T

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0.

i
o

Figure 6. Relationship of biostratigraphy to llthostratigraphy.

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

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

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

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

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

^LACM 65190
UCMP V687I

vUCMP V6893

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

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

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

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

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

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

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

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

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

The nannofossils collected include
Reticulofenestra umbilica (Levin) and Discoaster

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

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

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

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

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

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

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

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

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

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

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

POST-EOCENE DEPOSITS
Miocene

Andesite Dike

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

Pliocene and Pleistocene

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

San Diego Fornnation

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

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

Lindavista Formation

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

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

Bay Point Fornnation

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

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

Pleistocene and Holocene
Surficial Deposits

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

Stream-Terrace Deposits

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

I Landslide Deposits

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

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

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

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

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

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

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

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

**'Z'A

^^^^^l^p^r^^-^^^

,^^^^^^:i

-i*'^^^^^

-"^i:-

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

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

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

TRACE OF THE MOUNT SOLEDAD FAULT

LANDSLIDE
" DEPOSITS

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

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

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

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

FORT ROSECRANS LANDSLIDES

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

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

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

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

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

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

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CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

Alluvium and Slope Wash

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

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

Beach Deposits

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

Artificially Compacted Fill

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

STRUCTURE
AND SEISMIC HISTORY

r--

I Faults in the San Diego coasial area lie within a

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

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

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

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

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

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

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

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

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

SECTION B

La Mesa, Poway,

and SlVi/4 Escondido

quadrangles

ABSTRACT

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

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

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

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

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

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

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

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

(43)

GEOLOGY OF THE EASTERN SAN DIEGO METROPOLITAN
AREA, CALIFORNIA

La Mesa, Poway, and SWV4 Escondido quadrangles

by Michael P. Kennedy^ and Gary L. Peterson2

INTRODUCTION

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

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

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

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

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

PRE-EOCENE DEPOSITS
Basement Complex

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

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

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

Santiago Peak Volcanics

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

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

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

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

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

(45)

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN

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

OIn, LIndovista Formation

Tsd, San Diego Formation

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

Tf, Friars Formation

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

Formation
Kcss, Cobrillo Formation

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

Kg, Granitic rocks of ttie
souttiern California
batliollth

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

Plutonic Rocks of the
Southern California Batholith

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

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

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

Rosario Group

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

Lusardi Formation

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

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

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

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

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

EOCENE DEPOSITS
La Jolla Group

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

Friars Formation

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

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

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

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

Poway Group

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

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

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

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

.? °7i\° °l'° o°o°

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

Stadium Conglomerate

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

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

Mission Valley Formation

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

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

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

Pomerado Conglomerate

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

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

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

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

POST-EOCENE DEPOSITS
Pliocene and Pleistocene Rocks

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

San Diego Formation

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

Lindavista Formation

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

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

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

Pleistocene and Holocene
Surficial Deposits

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

St re a nn -Terrace Deposits

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

Landslide Deposits

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

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

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

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

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

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

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

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

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

Alluvium and Slope Wash

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

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

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

STRUCTURE
AND SEISMIC HISTORY

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

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

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

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

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

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

Table

?. Atterberg limits and

particle

size distribufion.

Location
{All San Bernardino
Base and Meridian)

Atterberg Limits

Particle Size

No. on
map

Liquid
limit

Plastic
limit

Plastic-
ity index

Sand
(%)

Silt
(%)

Clay

Mineralogy*

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

Mostly montmorillonite, some mica,
trace of kaolinite.

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

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

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

Mostly montmorillonite, trace of
kaolinite.

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

Mostly montmorillonite, trace of
quartz.

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

Mostly montmorillonite, trace of
kaolinite and quartz.

10 m vertically above number 5.

Mostly montmorillonite, trace of
quartz.

22 m vertically above number 5.

Mostly montmorillonite, trace of
quartz.

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

Mostly montmorillonite, minor
quartz.

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

Mostly montmorillonite, minor
quartz.

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

Mostly montmorillonite, minor
quartz, trace feldspar.

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

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

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

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

:ontinued on page following.

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Table

I. Atferberg limits and particle size disfribution

continued).

Location
{All San Bernardino
Base and Meridian)

Atterberg Limits

Particle Size

No, on
map

Liquid
limit

Plastic
limit

Plastic-
ity index

Sand
(%)

Silt
(%)

Clay

(%)

Mineralogy*

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

MINERAL RESOURCES

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

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

CALIFORNIA DIVISION OF MINES AND GEOLOGY

BULL. 200

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

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

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

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

Mines, quarries, or pits*

Location
{All San Bernardino
Base and Meridian)

Geologic unit

Mineral resource

Remarks

1. BIy Stone Co. Quarry.

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

Plutonic rock of the
southern California
batholith.

Dimension stone.

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

2. Van Deventer quarry
(Daley Corporation).

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

Plutonic rock of the
southern California
batholith.

Dimension stone.

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

3. Four-Gee deposit (Golem).

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

Santiago Peak Volcanics.

Pyrophyllite.

Discovered in 1952 and
mined since 1953.

4. Property now owned by
Rancho Bernardo Inc.

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

Plutonic rock of the
southern California
batholith.

Decomposed granite.

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

5. Black Mountain deposit;
Oliver Wylie estate.

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

Santiago Peak Volcanics.

Arsenopyrite (Arsenic)
minor amount of gold
and silver.

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

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

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

Plutonic rock of the
southern California
batholith.

Decomposed granite.

Inactive 1972; active in
1957.

7. Fletcher Quarries.

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

Plutonic rock of the
southern California
batholith.

Decomposed granite.

Inactive 1972.

8. Einer Brothers (Poway
Pit).

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

Plutonic rock of the
southern California
batholith.

Decomposed granite.

Inactive 1972.

9. Candel and Johnson
(Poway Operation).

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

Stadium Conglomerate.

Concrete sand and
crushed gravel.

Inactive 1972; active
1958.

10. Escondido Sand and
Gravel Works.

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

Alluvium derived
mostly from rocks of
the Poway Group.

Concrete and bituminous
aggregate.

Inactive 1958.

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

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

Stadium Conglomerate
and Alluvium.

Bituminous aggregate.

Active 1972.

12. Nelson and Sloan
(Miramar Plant).

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

Stadium Conglomerate
and Alluvium.

Concrete sand and
crushed gravel.

Began operation 1956,
active 1972.

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

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

Alluvium.

Concrete and plaster
sand, and crushed
gravel.

Inactive 1972.

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

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

Alluvium.

Concrete and plaster
sand, and crushed
gravel.

Operation began in 1954
in 200 acres; inactive
1972.

IS. Acme Truck Co. (Pit #1)

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

Plutonic rocks of the
southern California
batholith.

Decomposed granite.

Inactive 1972.

continued on page follov

1975

GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Table 2. Mines,

quarries, and pits in the

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

es (continued).

Mints, quarries, or pits*

Location
(All San Bernardino
Base and Meridian)

Geologic unit

Mineral resource

Remarks

16. Fletcher Quarries— Ed
Fletcher Co.

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

Santiago Peak Volcanics.

Riprap.

Used in construction of
Mission Bay Park and
jetty.

17. Industrial Asphalt (Plant
36).

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

Santiago Peak Volcanics.

Bituminous aggregate.

Active 1972.

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

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

Santiago Peak Volcanics.

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

Began operations 1929.

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

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

Alluvium.

Ceramic and concrete
sand.

San Diego River bed
sand operation.

20. Daley Corp.

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

Friars Formation and
Stadium Conglomerate.

Crushed gravel, for con-
crete and bituminous
aggregate.

Active 1972.

21. Denton, American Sand

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

Alluvium.

Plaster sand.

San Diego River bed; be-

Inc.

gan operations in 1951,
active 1972.

22. Nelson and Sloan, Mission
Sand Co.

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

Alluvium.

Plaster sand.

San Diego River bed; in-
active 1972.

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

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

Poway Group and Al-
luvium.

Concrete sand and
crushed gravel.

Active 1972.

24. Olswick Prospect.

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

Stadium Conglomerate.

Unidentified uranium
minerals.

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

25. Independent Stone Co.

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

Santiago Peak Volcanics.

Crushed stone.

Inactive 1972.

' Compiled in part from Weber, 1963.

CALIFO!..

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

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

BULL. 200

REFERENCES CITED

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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nia Norte, earthquakes of February, 1956; a field report;
Seismological Society of America Bull., v. 48, p. 101-116.

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Diego County. California: California Div. Mines and
Geology County Rept. 3, 309 p.

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tuff clasts in the upper Paleocene of southern California;
Geol. Soc. America Bull . v. 79, p. 1461-1486.

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

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— fj.

'-?- i-ltCtS

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

PREPARED IN
THE CITY

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

2H
C3

GEOLOGY OF THE DEL MAR QUADRANGLE
SAN DIEGO COUNTY, CALIFORNIA

by Michael P. Kennedy

SCALE 1 24000

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

EXPLANATION

[q7]

ArtiBcial fill

8 >o

i ^ c

g en ^

Landslide deposits

Stream-terrace deposita

Bay Point Formation

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

Lusardi Formation

Santiago Peak Volcanics

:ontrol by USGS and USC & GS

2.000' -

i.ooo* -

oeifle OcMfi

CARMEL VALLEY FAULT

Tsc

1,000'-

" ■// 111

Upp.r Cr.loc.0

.„..„„

,o..U„

„.,.„

...

TORREY PINES FAULT
SALK FAULT

SYMBOLS
Contact

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

Fault, showing dip

{dathed whtre appToximatelu located;

dotted where ameeaird: V. upthrown

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

Anticline, showing
direction of plunge.

Syncline, showing
direction of plunge.

X-

Strike and dip of bedding.

Landslide with direction of movement
indicated by arrows.

Clay sample locality.

Fossil mollusk locality.

Fossil coccolith locality.

Fossil vertebrate locality.

LOCATION MAP

11 If 11

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

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

PREPARED IN COOPE
WITH
THE CITY OF SAN [

PREPARED m COOPERATION

WITH

THE CITY OF SAN DIEGO

SAN D EGO METROPOLITAN AREA
BULLETIN 200 PLATE 3A

GEOLOGY OF THE POINT LOMA QUADRANGLE
SAN DIEGO COUNTY, CALIFORNIA

by Miohapl P. Kennedy

SCALE 1 24000

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

1975
EXPLANATION

Beach aand

I LOWER LOW WATER

Alluvium

Landslide deposits

I Qbp I

Bay Point Formation

Lin da vista Formation

Mount Soledad Formati<

Mission Valley Formation

Rosario Group

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

Contact

(dtuhed where approrimalcly loco

Fault, showing dip

(dathed wherf appranmateiy located;

dolled where concealed; U. uplhrown

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

-H-"

»y. «3

P A C I F/ I C

OCEAN

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

TOPOGRAPHIC BASE M/

Control by USGS and USC & G

Strike and dip of bedding.
Strike of vertical joint.

Landslide with direction of
indicated by arroT.

Fossil moUusk locality.

LOCATION MAP

. 20027 GEOLOGY \-

CHAEL P KENNEDY. 1970

ROSE CANYON FAULT ZONE

ISM

Ecoan« roeki undlfTsra

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

'9Si2'30"

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

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

SAN DIEGO METROPOLITAN AREA a ,

BULLETIN 200, PLATE 3B

117*00"

GEOLOGY OF THE LA MESA QUADRANGLE
SAN DIEGO COUNTY, CALIFORNIA

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

SCALE 1 24000

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

1975

EXPLANATION

Alluvium and Slopewash

Qstc, Slopewfuh: Qai & Qno. Alluvium and i

Landslide deposits

Lindavista Formation

San Diego Formation

Poway Group

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

Granite rocks

i of Ike eouthem Cali-

Santiago Peak Volcanics

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

"'0

2
>

OPOGRAPH C BASE
ConliolbyUSGSanc

Fault, showing dip

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

dolled where eonceaied: U. uplhrovm

Landslide with direction of movement
indicated by arrows.

Clay sample locality.

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

^^..

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

GEOLOGY OF THE POWAY QUADRANGLE
SAN DIEGO COUNTY, CALIFORNIA

by Michael P. Kennedy and G. L. Pet

SCALE 1 24000

1975
EXPLANATION

Alluvium and Slopewash

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

Landslide deposits

Lindavista Formation

Poway Group

Tp. Pomertulo Conolof

atone Tongue of Pomeru.. _ ..

ion Valley Formaiion: Ttl, Stadium Co'Ujiomerate.

Friars Formation

Lusardi Formation

Santiago Peak Volcanics

8 I

c - '2
5 5> T

'oximatelu located:

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

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

PREPARED IN COOPERATION

WITH

THE CITY OF SAN DIEGO

SAN DIEGO METROPOLITAN AREA (^3

BULLETIN 200, PLATE IB p^ ^

GEOLOGY OF THE SOUTHWEST QUARTER

OF THE ESGONDIDO QUADRANGLE

SAN DIEGO COUNTY, CALIFORNIA

by Michael P. Kennedy

SCALE 1:24000

1000 2000

4000 5000

Granite rocks

UndiffereiituUed oranilic rocks of the aoulhem Cali-
fornia batholith.

Santiago Peak Volcanics

Contact

idaahed where approximatdy located:
dotted where concealed)

dTI

Fault, showing dip

{dashed where approximately located:

CONTOUR INTERVAL 20 FEET

DOTTED LINES REPRESENT 10 FOOT CONTOURS

DATUM IS MEAN SEA LEVEL

1975
EXPLANATION

Zo
en

1
J

Qsw

Qal + Qsw

Alluviui

Qaw. Slopewath: Qal
undifferejttiated.

Lan(

n and Slopewash

d- Qsw. Alluvium arvi Slopewash

Qls

slide deposits

Tmv

Poway Group

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

Friars Formation

Control by USGS and USC & G

Contact

(dtuhed where approximalely located:
dotted where coTicealed)

Fault, showing dip

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

Strike and dip of bedding"^
in sedimentary rocks.

Strike and dip of bedding
in metasedimentary rocks.

Strike and dip of joint.
Strike of vertical joint.

Landslide with direction of movement
indicated by arrows.

LOCATION MAP

GEOLOGY MAPPED BY MICHAEL P KENNEDY. 1971

7*4^1

rf^S^Ji

A^T

fel

\^W

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