Geology of the San Diego Metropolitan Area, California

Physicai Sci .Li

2^ C3 A3 N0.2nn

California. Division of Mines and Geology, Bulletin. II.G.D. JiilU^Wtf^Ai Physical ScLLib.

TIM 24 OB $, A3 OLOGY OF THE no. 200 .METROPOLITAN AREA CALIFORNIA

Del Mar, La JoUa, Point Loma, La Mesa, Poway, and SWV4 Escondido 7V2 minute quadrangles THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA DAVIS o GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA

Prepared in cooperation witli the City of San Diego

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

SECTION B EASTERN SAN DIEGO METROPOLITAN AREA La Mesa, Poway, and SWV4 Escondido 7V2 minute quadrangles by Michael P. Kennedy and Gary L. Peterson

BULLETIN 200 1975

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

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STATE OF CALIFORNIA THE RESOURCES AGENCY EDMUND G. BROWN JR., GOVERNOR CLAIRE T. DEDRICK, SECRETARY FOR RESOURCES

DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY LEWIS A. MORAN, DIRECTOR THOMAS E. GAY JR., ACTING STATE GEOLOGIST

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III (^ » CONTENTS

SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA

ABSTRACT 9 INTRODUCTION 11 GEOLOGIC SETTING 13 PRE-EOCENE DEPOSITS 14 Santiago Peak Volcanlcs 14 Gabbro of the Southern California Bathollth 14 Rosario Group 15 Lusardi Formation 15 Point Loma Formation 15 Cabrillo Formation 15 EOCENE DEPOSITS 15 La Jolla Group 15 Mount Soledad Formation 16 Delmar Formation 16 Torrey Sandstone 16 Ardath Shale 18 Scripps Formation 18 Friars Formation 18 Poway Group 19 Stadium Conglomerate 19 Mission Valley Formation 19 Pomerado Conglomerate 19 FACIES RELATIONSHIPS OF THE EOCENE ROCKS 20 EOCENE BIOSTRATIGRAPHY 20 POST-EOCENE DEPOSITS 29 IVIiocene 29 Andesite Dike 29 Pliocene and Pleistocene 29 San Diego Formation 29 Lindavista Formation 29 Bay Point Formation 29 Pleistocene and Holocene Surficial Deposits 30 Stream-Terrace Deposits 30 Landslide Deposits 30 Alluvium and Slope Wash 35 Beach Deposits 35 Artificially Compacted Fill 35 STRUCTURE AND SEISMIC HISTORY 35 REFERENCES CITED 38

SECTION B - EASTERN SAN DIEGO METROPOUTAN AREA

ABSTRACT 43 INTRODUCTION 45 PRE-EOCENE DEPOSITS 45 Basement Complex 45 Santiago Peak Volcanics 45 Plutonic Rocks of the Southern California Bathoiith 47 Rosario Group 47 Lusardi Formation 47 EOCENE DEPOSITS 47 La Jolla Group 47 Friars Formation 48 Poway Group 48 Stadium Conglomerate 48 Mission Valley Formation 49 Pomerado Conglomerate 49

(3) POST-EOCENE DEPOSITS 49 Pliocene and Pleistocene Rocks 49 San Diego Formation 49 Llndavista Formation 50 Pleistocene and Holocene Surflclal Deposits 50 Stream- Terrace Deposits 50 Landslide Deposits 50 Alluvium and Slope Wash 51 STRUCTURE AND SEISMIC HISTORY 51 MINERAL RESOURCES 53 REFERENCES CITED 56

(4) ILLUSTRATIONS

SECTION A - WESTERN SAN DIEGO METROPOLITAN AREA

Plate 1A. Geology of the Del Mar quadrangle In pocket Plate 2A. Geology of the La Jolla quadrangle In pocket Plate 3A. Geology of the Point Loma quadrangle In pocket

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

1 Table . 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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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 unconformity 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 nonmarine 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 subsurface 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 indicates 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 nonmarine 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 metamorphic 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 succession 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 surficial 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 gently folded by the later episode include those of Upper Cretaceous and later age. Sediments approximately 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 between 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 incompetent 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 use in the north county, Del Mar, La Jolla, Miramar, - Lindavista and Point Loma areas. The are a is un- In 1965 the California Division of Mines and derlain primarily by sedimentary rocITiTiowever, oc- in with Geology cooperation the City of San Diego casional outcrops of plutonic and metamorphic a geologic investigation began comprehensive aimed rocks do occur. Very small surficial landslides at a better understanding of the geologic hazards (mostly unmapped due to scale of map) associated that exist within the greater San Diego metropolitan with expansible clay deposits in the northern and area This report is (Kennedy, 1967, 1969). one eastern parts of the area are abundant. These land-_ product of that investigation is complemented and slides are closely associated with the outcrops of by a similar report on the La Mesa, Poway, and Friars and Dclmar Formations. The rock units map- SWi/-* Escondido quadrangles (Kennedy and Peter- ped and discussed herein are shown in diagram- son, 1975). Together the Del Mar, La Jolla, and matic relationship in figure 2. Point Loma quadrangles are approximately 350 Previous investigations that have been square kilometers (km^) in extent and constitute the especially useful in this study include a ground western part of the greater San Diego metropolitan water investigation by A.J. Ellis (1919), a area (figure I and photo 1 ). stratigraphic and paleontologic thesis of the La Jolla The western San Diego metropolitan area is un- quadrangle by M.A. Hanna (1926), studies of the derlain sand, gravel, and clay resources by valuable Pliocene deposits of San Diego by L.G. Hertlein and deemed feasibly extractable in today's market for U.S. Grant IV (I 939, 1944), a monograph on the

'Geologist, Californij 1 of Mines and Geology mineral resources of San Diego County by F.H.

(11) CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

^ y<> LAKE HODGES

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

WOODSON MOUNTAIN POWAY QUADRANGLE -^ (Plate 2B)

/ QUADRANGLE (Plate 3B)

Figure 1. Index map stiowlng the location of the Del Mar, La Jolla. and Point Loma quadrangles. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 13

complex upon which the younger sedimentary suc- COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN cession rests. See figure 2 and cross sections A-A' (plate lA), B-B', C-C (plate 2A), and D-D"

Point (plate 3A). C» Qbp '^''P- S°y Formation I •••• The Santiago Peak Volcanics (Black Mountain Qin I Qln, Lindovisto Formation Volcanics of Hanna, 1926) rest with angular unconformity on the Bedford Canyon Formation where Tsd, Son Diego Formation the latter has been preserved. The Bedford Canyon Formation is not known to exist at the surface in Tp, Pomerodo Conglomerate Tmv, Mission Valley Formation this area. In the Santa Ana Mountains to the north, Tst, Slodium Conglomerate the Santiago Peak Volcanics have an exposed length

of 1 30 km (Larsen, I 948), and to the south they ex- Tf, Friars Formation tend from the international boundary to near the Tsc, Scripps Formotion Ta, Ardoth Stiale center of Baja California (Allison, 1964). They oc- Tt, Torrey Sandstone cur in the subsurface throughout most of the Td, Delmar Formation southern California continental margin (Hertlein Tms, Mount Soledod Formation and Grant, 1944; Gray et ai, 1971). Kcss, Cabrillo Formation (sandstone part) The Santiago Peak Volcanics have undergone Kccg, Cabrillo Formation mild metamorphism and have been intruded by (conglomerate part) rocks of the southern California batholith. The Kp, Point Loma Formation plutonic rocks of the batholith that crop out in the Kl, Lusardi Formation Jsp, Santiago Peak Volcan mapped area are gabbros, which have a steeply inclined contact with the older metamorphic rock.

Kg, Granitic rocks of the The southern California batholith forms the southern California backbone the Peninsular Ranges of southern bathollth of 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- Figure 2 Columnar section of the San Diego continental nia peninsula on the south. The batholithic rocks margin. within the study area were named and described by Larsen (1948). Deposition of Upper Cretaceous clastic marine Weber (1963), and the San Diego-El Centre and nonmarine strata followed the emplacement, geologic map sheet by R.G. Strand (1962). uplift, unroofing, and deformation of the southern California batholith (figure 3). The basal formation The author would like to extend special thanks of the clastic succession is the Lusardi Formation, a to D.M. Morton and G.W. Moore of the United boulder fanglomerate that forms the base States Geological Survey for encouragement, help in nonmarine of the Rosario Group. The Lusardi Formation was the field, and many valuable discussions pertinent to laid down along the western margin of the tectonic this study. Acknowledgment is due also to M.O. a deeply weathered surface of Woodburne and M.A. Murphy of the University of highlands and upon California Riverside and Professor A.O. Woodford the plutonic and metamorphic rock (Peterson and Nordstrom, 1970). The clasts of the Lusardi For- of Pomona College for long interest in this study mation are composed essentially of these two rock and enthusiastic help in the field and laboratory; to types, suggesting a local source area (Nordstrom, D. Bukry, D.J. Golz, C.R. Givens, J. P. Kern, ED. Point Formation is the in- Milow, W.J. Zinsmeister, and the late E.C. Allison 1970). The Loma termediate formation of the Rosario Group. It un- for assistance in the paleontologic aspects; A.K. derlies of the Point Peninsula and the Baird for help in petrographic aspects; P.K. Morton, most Loma hills southeast of La Jolla and is conformably C.H. Gray, Jr., G.B. Cleveland, B.W. Troxel, F.H. overlain by marine sandstone and conglomerate of Weber, Jr., Y.H. Smitter, R.G. Strand, G.L. Peter- the Cabrillo Formation. The Cabrillo Formation is son, and J.I. Ziony for many interesting discussions the formation of the Rosario Group and in the field and for reviewing the maps and uppermost manuscript. 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- GEOLOGIC SETTING conformity, figure 3) is marked by residual clay deposits of montmorillonite that grade downward to Pre-Eocene rocks in the southern Peninsular fresh basement rock and upward into the Eocene Ranges of California are subdivided into four major sedimentary rock. The decomposed granitic rock units. From oldest to youngest they include the Bed- and clay were primary sources of sediment for the ford Canyon Formation, Santiago Peak Volcanics, Eocene depositional basin and give rise to the southern California batholith, and the Rosario granitic appearance of the arkosic sandstone of Group. Together these units form the basement these sedimentary facies. 14 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

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

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

I^S^xl Rocks of the southern California batholith

IW;V/| Rocks of the Santiago Peak Volcanics

Figure 3. Diagrammatic sketch Intrusive contact between of the basement complex and Sub-Rosario the Santiago Peak Volcanics superjacent strata. Sub-La Jolla unconformity and the southern California Present day unconformity batholith topography

PRE-EOCENE DEPOSITS Age estimates for the Santiago Peak Volcanics have ranged from Late Triassic (Hanna. 1926) to

mid-Cretaceous (Milow and Ennis, 1961 ). Fife et al. Santiago Peak Volcanics (1967) reported latest Jurassic (Portlandian) fossils from a marine clastic part of the succession near The Santiago Peak Volcanics comprise an Del Mar, and to date this constitutes the most elongate belt of mildly metamorphosed volcanic, reliable age for these rocks in the San Diego area. 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- Gabbro of the 204) for exposures in the northeast part of the area. Southern California Batholith Larsen (1948) substituted the name— Santiago Peak Volcanics — as the name "Black Mountain" was pre- Larsen (1948) named the batholithic rocks in empted. the San Diego coastal area the Woodson Mountain The volcanic rocks range in composition from Granodioriie, the Bonsall Tonalite, and the San basalt to rhyolite but are predominantly dacite and Marcos Gabbro. Though most of the plutonic rocks andesite. The succession is typified by a wide in proximity to San Diego are quartz diorite and variety of breccia, agglomerate, volcanic granodiorite, only gabbro crops out within this area. conglomerate, and tine-grained tuff and tuff breccia. The gabbro varies considerably in texture and com- Highly silicified rock — probably tuff and a variety of position but generally is coarse grained and dark dark, dense, tine-grained hornfels — occur locally. In gray. The chief mineral constituents are calcic feld- the Del Mar quadrangle, fossil-bearing marine spar and pyroxene with minor amounts of quartz sedimentary rocks are interbedded with the volcanic and biotite. and volcaniclastic rocks. Included with the Santiago Potassium-argon dates (Evernden and Kistler, Peak Volcanics are a number of small mildly 1970) from a gabbro located 20 km northeast of Del metamorphosed gabbroic to granodioritic plutons Mar near San Marcos, and a quartz diorite located which arc considered to have been feeders for the 10 km southeast of Escondido are, respectively, 101 volcanics rather than parts of the southern Califor- and 105 million years. A lead-alpha date on zircon nia batholith. from quartz diorite in the Woodson Mountain area, The Santiago Peak Volcanics, which form 20 km southeast of Escondido, is 105 ± 10 million elevated peaks immediately east of the area at Black years (Bushee ct al. 1963). Mountain, are hard and extremely resistant to Throughout most of its exposure, the gabbro is weathering and erosion. Most of the volcanic rocks weathered and difficult to distinguish from overlying arc dark greenish gray where fresh and weather sedimentary formations, which are largely com- grayish red to dark reddish brown. The soil posed of weathered plutonic basement rock. Careful developed on the Santiago Peak Volcanics is the examination for relict features, such as small quartz color of the weathered rock and s upports the growth veins, is necessary to distinguish the weathered rock of dense chaparral. from the overlying sedimentary strata. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 15

6° Rosario Group (Turner et al., 1 968, p. 8). With a shoreline dip of E., it is postulated that 190 m of section may be ad- Cretaceous Rosario Group is com- The Upper ded below low-tide level to the observed thickness of marine and posed of clastic sedimentary rocks of the formation. This submarine information, com- to the Lusardi, Point nonmarine origin assigned bined with interpolation from well logs, suggests Formations. Loma, and Cabrilio that the total thickness of the Point Loma Formation at its type locality is about 300 m (section D-D'). Lusardi Formation Fossil Foraminifera and calcareous nan- The basal formation of the Rosario Group, the noplankton indicate a Late Cretaceous age for the Lusardi Formation, was named by Nordstrom Point Loma Formation (filter, 1968; Bukry and (1970) for exposures of boulder conglomerate near Kennedy, 1969). Foraminifera from near the base of the confluence of Lusardi Creek and the San the formation at Carlsbad are middle to upper Cam- Dieguito River, 2 km north of the area in the Rancho panian in age, whereas those from the uppermost Santa Fe quadrangle. beds are lower Maestrichtian in age (Sliter, 1968). These rocks consist of cobble and boulder The exposed part of the Point Loma Formation conglomerate, with occasional thin lenses of correlates with the Williams Formation and the up- medium-grained sandstone. Some of the clasts are per part of the Ladd Formation in the Santa Ana 10 m in diameter. The Lusardi Formation at the ex- Mountains (Popenoe et at., 1960) and with the mid- posures within the northeast quarter of the Del Mar dle part of Seal's (1924) Formacion Rosario in nor- quadrarigle, and within theType'area to the north, thern Baja California. 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 Cabrilio Formation belong to the Lusardi Formation are 82 m thick, The Cabrilio Formation, the uppermost unit of at Point No. 1 well, 10 north whereas the Loma km the Rosario Group, is exposed on the Point Loma of Point Loma, these rocks are 295-376 m thick Peninsula from the southern tip north to Sunset (Hertlein 38). The Lusardi For- and Grant, 1944, p. Cliffs. At Pacific Beach in the sea cliffs, it is ex- mation at its type area is unconformably overlain by posed from 300 m south of False Point to Bird Rock near Carlsbad, Eocene rocks, but 16 km to the north on the north and at La Jolla in an S-shaped belt it is overlain conformably by siltstone and sand- around the noses of the Pacific Beach syncline and and stone of the Point Loma Formation (Kennedy Mount Soledad anticline. In the sea cliff at its type Moore, 1971b). section 250 m east of the new Point Loma The Lusardi Formation is considered to b e Late lighthouse, it consists of massive medium-grained Cretaceous in age because it contains quartz diorite sandstone and cross-bedded cobble conglomerate bouIdeHlleroded from the mid-Cretaceous southern containing fresh plutonic and metavolcanic clasts California, batholith, which has a minimum age of but lacking red porphyritic rhyolite-tuff cobbles 105± 10 million years (Bushee et al., 1963), and it characteristic of nearby Eocene rocks. is overlain by the Point Loma Formation which con- Throughout the mapped area, the Cabrilio For- tains Upper Cretaceous (Campanian) Foraminifera mation conformably overlies the Point Loma For- (Sliter, 1968). mation. The formation is 8 1 m thick at its type

The Lusardi Formation is lithologically locality, where it is uncontorrnaSTy overlain by equivalent to the Trabuco Formation of the Santa Pleistocene deposits. Along the sea cliff at False Ana Mountains on the north (Nordstrom, 1970), to Point, it has a thickness of 170 meters. an unnamed fanglomerate near the base of the A clam from the east flank of Mount Soledad Williams Formation, also in the Santa Ana Moun- within the lower 5 m of the Cabrilio Formation has tains (Morton, 1972, p. 39), and to the Redondo been identified as "Pharella" alta (Gabb) and Formation of Flynn (I 970) in northern Baja Califor- assigned to the Maestrichtian (L. Saul, written com- nia. munication, 1969). The Cabrilio Formation correlates with the upper part of the Formacion Rosario of Beal (1924) in northern Baja California Point Loma Formation and possibly with the upper part of the Williams The Point Loma Formation, the intermediate Formation in the Santa Ana Mountains. 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 EOCENE DEPOSITS 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 La Jolla Group shale that occur in graded beds about 30 cen- The La Jolla Group (La Jolla Formation of timeters (cm) thick. Hanna, 1926) ranges from moderately deep-water, Scuba-diving observations- 1860 m offshore fine-grained siltstone, to sandy beach and lagoonal from the type locality show that ledgy pavement-like facies, and coarse-grained continental sandstone sandstone, similar to that in the lower half of the ex- and conglomerate. Deep water fine-grained facies posed section, continues to a depth of at least 37 m predominate to the southwest, whereas the lagoonal 16 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

and continental facies are more abundant to the nor- plagioclasc (1-2 percent), biotite (1-2 percent), and theast. These units include six partly intertonguing a trace of epidote, pyroxene, and hematite. and partially time equivalent formations, which from The Ardath Shale, conformably overlying the oldest to youngest, are the Mount Soledad For- Mount Soledad Formation, contains fossils which mation. Delmar Formation, Torrey Sandstone, Ar- are lower middle Eocene in age (Bukry and Ken- dath Shale. Scripps Formation, and Friars For- nedy, 1969). The Mount Soledad Formation mation (figure 4). correlates with the basal part of the Santiago For- mation in the Santa Ana Mountains (Kennedy and Mount Soledad Formation Moore, 1971a). Southwest of the Rose Canyon fault, which in Rose Canyon displaces rocks on its southwest side Delmar Formation

(figure 4 plate 2A; section B-B' ). an Eocene marine ; The Delmar Formation (Delmar Sand Member cobhic conglomerate and sandstone unit, designated of Hanna, 1926) is exposed from the northern edge the Mount Soledad Conglomerate (part of the Rose of the area mapped for 9 km south to Soledad Valley Canyon Shale Member of Hanna, 1926), rests un- where it is overlain by younger rocks(plate 1 A).The conformably on rocks the Upper Cretaceous of stratigraphic relationship of the Delmar Formation Cabrillo Formation. This formation crops out with the Mount Soledad Formation, Torrey Sand- around the Mount Soledad anticline in La Jolla and stone, and Ardath Shale is shown in figure 4. northern Pacific Beach and south of Mission Bay on Most of the Delmar Formation is dusky the southwest Hank of the Pacific Beach syncline yellowish-green sandy claystone interbedded with (plates 2A, 3A). Block diagrams 3, 5, and 6 (figure4) medium-gray coarse-grained sandstone. Several show the stratigraphic relationship of the Mount resistant beds composed of Ostrea idriaensis Gabb Soledad Formation and the overlying and partly in- and other brackish-water mollusks indicate a tertonguing Ardath Shale, Delmar Formation, and lagoonal origin. The sandstone is typically com- Torrey Sandstone. At its type locality on Mount posed of quartz (80-85 percent), potassium feldspar Soledad, the formation is 69 m thick and consists of (10-15 percent), plagioclase (1-2 percent), biotite cobble conglomerate with minor beds of sandstone. (2-3 percent), and a trace of hematite, topaz, The conglomerate content of the formation is glauconite, and pyroxene. The claystone is com- variable to the southeast where it is locally composed of montmorillonite and kaolinite. posed entirely of medium-grained sandstone. The The base of the formation is not exposed but is conglomerate commonly overlies similar Upper presumed to rest unconformably on Upper Cretaceous conglomerate of the Cabrillo Formation. Cretaceous or older rocks (section A-A' ) or con- The presence of distinctive red porphyritic, soda formably on the Mount Soledad Formation as do rhyolite-tuff clasts in the Mount Soledad Formation correlative formations to the north and south (sec- differentiates it from the Cabrillo Formation. This tion B-B' ). In its type section near the town of Del difference is easily seen at a sea-cliff exposure 300 Mar and throughout the area, it is overlain m northwest of the end of Tourmaline Street in gradationally by the Torrey Sandstone, with which it Pacific Beach where the two conglomerates are in is also partly equivalent (figure 4). In the subsurface contact (photo 2). The sandstone is moderately well 15 km north near Carlsbad, the Delmar Formation sorted, subangular to subrounded, poorly indurated, grades into the Santiago Formation, and its boun- and well bedded. It consists of quartz (75-80 per- dary with the Santiago Formation occurs directly cent), potassium feldspar (20-25 percent). 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 northern 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 composed of arkosic sandstone which is white to light brown, medium to coarse grained, subangular, and

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^\ CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

Torrey Pines grade on Highway 101, the contact basal part of the Torrey Sandstone and with the mid- with the underlying Deimar Formation consists of dle part of the Santiago Formation. an alternating gradation between white sandstone beds above the dusky yellow-green t'ossiliferous Scripps Formation claystone beds below. Approximately 13 km to the north, the Torrey Sandstone grades into and is The Scripps Formation (part of the Rose overlain by the Santiago Formation. In Soledad Canyon Shale Member of Hanna, 1926) underlies Valley the lower part grades into and is overlain by much of the area from east of Del Mar on the north the Ardath Shale and the upper part by the Scripps to the mouth of Mission Valley on the south (plates Formation (Kennedy and Moore, 1971a). The I A-3A). Along the coast, it extends from the middle distribution and stratigraphic relationship of the of Torrey Pines Park to Scripps Institution of Torrey Sandstone with respect to its related facies is Oceanography. The type section of the Scripps For- shown in figure 4. mation is 1 km north of Scripps Pier, on the north side of the mouth of Blacks Canyon (Kennedy and The Torrey Sandstone is believed to have been Moore, 1971a). Here it consists of 56 m of pale deposited along a submerging coast on an arcuate yellowish-brown, medium-grained sandstone and barrier beach that enclosed and then later tran- occasional cobble-conglomerate interbeds. The sgressed over Deimar lagoonal sediments. Its sandstone is composed of subangular grains of deposition was arrested when submergence slowed quartz (75-80 percent), potassium feldspar (15-20 and the shoreline retreated. Although the Torrey percent), biotite (2-5 percent), plagioclase (less than Sandstone contains only a few poorly preserved 1 percent), and a trace of epidote, pyroxene, tour- fossils and fossil casts, its middle Eocene age is fir- maline, sphene, and apatite. Both the basal contact mly established by its interfingering relationship with the Ardath Shale and the upper contact w ith the with the well-dated Ardath Shale. Friars Formation are conformable. Figure 4 illustrates the stratigraphic relationship between the Ardath Shale Scripps Formation and related facies. Several The Ardath Shale (part of the Rose Canyon tongues belonging to the Scripps Formation occur in Shale Member of Hanna, 1926) crops out along the the section. The largest of these is mapped in the sea cliffs from Bathtub Rock in Torrey Pines State vicinity of Sorrento Valley (plate lA). Park, south to the pier at Scripps Institution of Fossils are present but are less common in the Oceanography, where it is overlain by Pleistocene Scripps Formation than in the underlying Ardath deposits (plates 1 A, 2A). From Rose Canyon it can be Shale. Because of its close conformity and partial in- traced south to the northeast corner of Mission Bay, tcrgradation with the Ardath Shale, the Scripps For- where it is overlain by younger rocks. In the nor- mation is considered to be middle Eocene. To the thwest corner of the area, it thins below the Scripps north near Encinitas it correlates with the upper part Formation as it grades into the Torrey Sandstone of the Torrey Sandstone and, farther to the north in below. The stratigraphic relationship between the the Santa Ana Mountains, with the middle part of Ardath Shale and formations with which it in- the Santiago Formation. terfingers is illustrated in figure 4. The Ardath Shale is predominantly weakly fissile, olive-gray shale. Friars Formation Concretionary beds containing molluscan fossils are The middle and late Eocene Friars Formation common. Expansible claystone locally comprises as (part of the Shale of Hanna. much as 25 percent of the unit and landslides are Rose Canyon Member commonly associated with those areas. Sieve 1926) is the uppermost unit of the La Jolla Group. rocks are nonmarine and lagoonal analyses indicate that the particle size distribution The sandstone and claystone named for exposures along the north is 81 percent silt, 16 percent clay, and 3 percent side of Mission Valley near Friars Road in the La sand. The clay is mostly kaolinite but mont- Jolla quadrangle (Kennedy and Moore. 1971a). The morillonite is also present. The sand consists of sandstone is quartz (70-75 percent), potassium feldspar (15-20 composed of quartz (75-80 percent), potassium feldspar (10-15 percent), biotite (5-10 percent), biotite (5-10 percent), plagioclase (less percent), plagioclase (less than 1 percent), and a than I percent), and a trace of zircon, tourmaline, pyroxene, and amphibole. trace of amphibole. pyroxene, hematite, and tourmaline. The claystone is composed of mont- The base of the Ardath Shale is not at exposed morillonite and kaolinite. Friars Formation is its type section in Rose Canyon (Kennedy and predominantly a nonmarine and nearshore marine Moore, 1971a), but underlying outcrops at the type facies which reaches a maximum thickness of 50 m locality of the Mount Soledad Formation, 1 km to between Mission Valley and Carmel Valley. The the west, reveal the contact on the Soledad Mount sandstone is typically massive, yellowish gray, Formation to be conformable. The Ardath Shale is medium grained, and poorly indurated with estimated to be 70 m thick at its type locality. It subangular to subrounded grains. Caliche-rich sand- grades alternatingly and conformably into the stone beds are locally interlayered with dark overlying Scripps Formation. greenish-gray sandy claystone. Cobble conglomerate Abundant fossils, including mollusks and lenses and tongues of Huviatile origin are charac- calcareous nannoplankton, permit an assignment of teristic of the easternmost exposures. The Friars the Ardath Shale to the lower middle Eocene (Bukry Formation rests unconformably on rocks of the and Kennedy, 1969). The unit correlates with the basement complex and conformably on the Scripps 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 19

Formation. It is in turn overlain by other sedimen- Mission Valley Formation tary deposits of Eocene, Pleistocene, and Holocene The Mission Valley Formation, a predominan- age. The Friars and Delmar Formations are tly marine sandstone unit, lies conformably upon the lithologicaiiy identical in their central and nor- Stadium Conglomerate and is in turn conformably theastern exposures, and they have been un- overlain by the Pomerado Conglomerate. It has a differentiated in these areas on the geologic map. maximum thickness of 60 m and was named for ex- The stratigraphic relationship between the posures along the south wall of Mission Valley on Friars Formation and related facies is diagram- the west side of State Highway 163 (Kennedy and matically illustrated in figure 4. 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 Poway Group subrounded and locally range in size from coarse to The Poway Group (Poway Conglomerate of very fine sand. Plagioclase and biotite are also Hanna, 1926) includes three partly intertonguing present but generally constitute less than 2 percent and partially time equivalent formations, the each. Cobble conglomerate tongues within the Stadium Conglomerate, the Mission Valley For- Mission Valley Formation, similar to Stadium mation, and the Pomerado Conglomerate. These Conglomerate, comprise up to 30 percent of sec- rocks are primarily nonmarine in their easternmost tions measured in the easternmost exposures of the exposures and nearshore marine and lagoonal in area but less than 1 percent of sections measured their westernmost exposures. along the westernmost outcrops. Because of the friable nature of the Mission Stadium Conglomerate Valley Formation, it lacks the bold topographic ex- The type section of the Stadium Conglomerate pression displayed by the Stadium Conglomerate. lies near the boundary between the La Jolla and La Interbeds and tongues of claystone of brackish Mesa quadrangles along the northern wall of water origin locally compose 20 percent of the sec- Mission Valley near San Diego Stadium (Kennedy tion. The clay is primarily montmorillonile but and Moore, 1971a). At the type section the for- kaolinite is also present. The Mission Valley For- mation consists of a massive cobble conglomerate mation thins from the west to the east (figure 4) and with a dark yellowish-brown coarse-grained sand- pinches out in the eastern part of the Poway and La stone matrix. The conglomerate contains dispersed Mesa quadrangles. The rocks are often fossiliferous lenses of fossiliferous crossbedded sandstone. The and contain a molluscan fauna in the western and fossils include calcareous nannoplankton of late? central exposures and a land-mammal fauna in the Eocene age. eastern exposures. One molluscan assemblage, collected from the uppermost beds of the formation The Stadium Conglomerate is moderately well in east of the Miramar Reser- sorted with an average clast size in the cobble range. a road cut 200 m due (elevation at Lat. 32° Clasts having diameters as large as .05 m do occur voir filtration plant 238 m) 54.8' 117° 05.7" W., is reported by C.R. but are rare. The sandstone matrix constitutes less N.; Long. (written communication, 1970) to be charac- than 20 percent of the unit, but in local stratigraphic Givens sections individual sandstone beds and lenses con- teristic of the upper Eocene (Tejon Stage) and of Europe. stitute 50 percent of the unit. correlative with the upper Eocene The highly distinctive "Poway" clasts that occur only within Cenozoic deposits of southern Califor- Pomerado Conglomerate nia and that typify the Stadium Conglomerate con- The Pomerado Conglomerate, the uppermost sist predominantly (up to 85 percent) of slightly ft)rmation of the Poway Group, has a maximum to volcanic metamorphosed rhyolitic dacitic and thickness of 55 meters. It was named for exposures volcaniclastic rocks and up to 20 percent quartzite. located at the divide between Carroll Canyon and The source area for these clasts is controversial, Poway Valley along Pomerado Road east of the area and potential sources from the Mojave Desert to in the Poway quadrangle (Peterson and Kennedy, etal., Sonora, Mexico, have been proposed (DeLisle 1974). The Pomerado Conglomerate is late Eocene et al.. 1965; Merriam, 1968; Woodford 1968; in age and is a massive cobble conglomerate Minch, 1972). Based on direction of pinching and lithologicaiiy identical to the Stadium cobble imbrication, the clasts within the Stadium Conglomerate. The contact between the Mission within Conglomerate were deposited the San Diego Valley Formation and Pomerado Conglomerate is embayment by a westward-flowing river system. conformable and gradational. The Pomerado Based on clast size the conglomerates were Conglomerate is characterized by occasional thin probably derived from a now eroded source within beds, lenses, and tongues of light-brown medium- 150 km of their present position (Kennedy, 1973a). grained sandstone. One of the largest of these, The Stadium Conglomerate is conformably un- which crops out east of the area near Miramar derlain by the Friars Formation and is conformably Reservoir in the Poway quadrangle, is designated overlain by the Mission Valley Formation. The the Miramar Sandstone Member (Peterson and Ken- stratigraphic relationship between the Stadium nedy, 1974). Lithologicaiiy the Miramar Sandstone Conglomerate and genetically related Eocene Member is identical to the Mission Valley For- conglomerate to the east is shown in figure 4. mation but is stratigraphically higher and wholly 20 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

contained within the Pomerado Conglomerate. It has removed parts of the cyclic facies. The cycles in the a maximum thickness of 10 m in its type area and is San Diego embayment are gradational, complete, considered to be late Eocene in age based on its and considered to have originated under different superpositional relationship with the Pomerado conditions. (^ Conglomerate and Mission Valley Formations. 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- FACIES RELATIONSHIPS OF sidence and rate of sedimentation. Regressive deposits are formed by the slowing of subsidence THE EOCENE ROCKS and/or an increase in sedimentation which creates the outward building of the shoreline and shallowing by infilling of the basin. During periods The Eocene rocks of the San Diego embayment of more rapid subsidence and/or the slowing of were laid down on a narrow continental shelf and sedimentation rate, the basin deepens and tran- adjacent margin that extended northwest and sgressive deposits are laid down. southeast for more than 50 kilometers. Subsidence Figure 5 is a diagrammatic illustration of the of the basin and repeated change in sediment tlux second model. Beginning at the top of figure 5 with resulted in alternating advances and retreats of the diagram A, subsidence is occurring at a rapid rate shoreline. The advances are recorded by the with respect to sediment influx. This shows the deposition of time-lransgressive rock units and the initial development of the lagoon, beach, and near- retreats by their time-regressive counterparts (Ken- shore deposits. Diagrams B and C illustrate later nedy, 1971; 1973). time but with continued conditions as represented Nonmarine lagoonal and nearshore marine by A. Note that these units are time-transgres'sive facies were deposited on the east and marine con- and that sea level has advanced over the old land tinental shelf facies on the west side of the San surface. Beginning with diagram D either a slowing Diego embayment. There are two lithostratigraphic in the rate of subsidence has occurred or the groups divided into nine intertonguing formations sedimentation rate has increased or both. As a that together are approximately 700 m thick. The result of this change, the first regressive deposits formational names are those of Kennedy and Moore are formed and the shoreline retreats. (1971a) and Peterson and Kennedy (1974). A period of rapid subsidence and high sediment- y- The two groups are the La Jolla and Poway. The ation marks the beginning of the first transgression, /^ La Jolla Group is slratigraphically lower and lies recorded by the deposition of the Delmar For- / predominantly west of the Poway Group. Deltaic mation, Torrey Sandstone, and Ardath Shale. These conglomerate and sandstone, lagoonal sandstone sediments transgressed eastwardly over and beyond / and claystone, beach sandstone, and marine shale the Mount Soledad Formation into pre-Eocene / constitute the La Jolla Group. Deltaic conglomerate basement rock (section B-B'). The Ardath Shale \ and sandstone, lagoonal sandstone, and littoral rests conformably upon the Mount Soledad For- sandstone and siltstone comprise the Poway Group. mation at the type section of the Mount Soledad / Figure 4 illustrates the interrelationships of the Formation located 600 m east of Easter Cross in La rocks and the contact between the groups. Jolla. The Torrey Sandstone rests gradationally Deposition occurred continuously in the San upon the Mount Soledad Formation at the base of ' Diego embayment for a period of nearly 10 million Indian Trail in the sea cliffs 3300 m north of years during which time the regional tectonic down- Scripps pier and at the intersection of Carmel Valley warping of the basin took place. The subsidence is and Soledad Valley (plate lA). The conglomerate marked in the stratigraphic record by two prominent shown within the lower Delmar Formation is con- marine transgressions and two intervening sidered to represent the transitional facies between ^egressions. the Delmar and Mount Soledad Formations. /

There are two somewhat conflicting hypotheses As shown in figure 4 and plates 1 A-3A ,the tran- used to explain the development of cyclic sedimen- sgressive nature of these stratigraphic units is in- tation of this type (Sears et al.. 1941). The cyclic dicated by their superpositional and lateral relation- stratigraphic succession that forms by either of the ship. The lagoonal deposits are predominantly low two is an intertonguing sequence of strata having in the section and lie to the east and northeast of the time regressive and transgressive parts (i.e., marine, beach-bar and marine deposits. The beach and littoral, beach, nonmarine) that grade laterally and beach-bar deposits grade laterally eastward and vertically with respect to each other. downward into lagoonal deposits and westward and One hypothesis or model, which has been rejec- upward into marine deposits. Marine deposits are ted for the development of the San Diego em- high in the section and lie to the west of the beach bayment, involves alternating upward and downward and lagoonal deposits. movement of the marine basin and adjacent con- A slowing in subsidence and/or an increase in tinental land mass to create the necessary change in sedimentation to a degree that allowed infilling of sea level. The erosion of previously deposited the embayment at a greater rate than subsidence materials by waves, during times when uplift oc- marks the beginning of a retreating shoreline and curred faster than sedimentation, would have the development of regressive deposition. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 21

1 22 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

As shallowing occurred the lagoonal. beach, of the Tertiary mammal chronology can be directly and marine deposits migrated westward creating a compared with invertebrate chronologies (figure 6). reversal in their superpositional relationship (figure Four major fossil groups have been collected 4), Again the lagoonal rocks lie predominantly on from the Eocene rocks of the San Diego embayment. the cast and marine rocks predominantly on the These include I) mammals, 2) mollusks, 3) west, but the regressive lagoonal rocks comprise the calcareous nannoplankton, and 4) Foraminifera upper part of the stratigraphic sequence and the (figures 7-9). marine rocks the lower part. The regressive lagoonal equivalent of the tran- 1) Mammalian fossils were collected from the Ar- dath Shale, Friars Formation. Stadium sgressive Delm.'r Formation is the Friars Formation Conglomerate, and Mission Valley Formation. The and that of the beach-bar Torrey Sandstone is the collection has been studied (Golz. 1971, 1973) and Scripps Formation. The Ardath Shale also has a found to be correlative In its stratlgraphically up- regressive however, trangressive and phase; these permost part with the North American Uinta C have not been separated, as they constitute a con- Mammal Age and in Its lowest part with Bridgerian tinuous section that is lithologically homogeneous. Mammal Age.

Interbeds, tongues, and lenses of cobble 2) Molluscan fossils were collected from Mount conglomerate composed of exotic tuffaceous clasts, Soledad Formation. Delmar Formation, Torrey Sand- mostly of rhyolitic composition, and the primary stone. Ardath Shale. Scripps Formation. Friars For- sediment of a significant westwardly or nor- mation, and Mission Valley Formation, The fossils thwestwardly flowing river system are abundant in have been correlated, using West Coast (Califor- nia) Molluscan Stages, with the Tejon Stage in the this part of the section. The direction of transport is stratlgraphically uppermost part of the section, the indicated primarily by cobble imbrication and "Transition Stage" in the intermediate part, and the paleostream channel mapping (Minch. 1972). In the Domengine Stage in the lower part (Hanna. 1926; central and eastern part of the embayment, thick Moore, 1968; C. R. Givens, written communication. deposits of these clasts form the Stadium and 1973). Pomerado Conglomerates. 3) Calcareous nannoplankton have been collected Renewed subsidence and/or a slowing of from the Ardath Shale. Scripps Formation, Stadium deposition marked a second transgressive cycle and Conglomerate, and Mission Valley Formation. The rocks of nearshore marine and nonmarine origin flora in the stratlgraphically lowest part of the sec- were laid down. The transgressive nature of the tion IS indicative of the middle Eocene. Lutetian Stage of Europe (Bukry and Kennedy. strata can be detected by the superpositional and 1969). The flora from the uppermost beds collected is sparse gradational relationship between and within the and is questionably correlative with the lower part Mission Valley Formation and the Stadium of the upper Eocene (D. Bukry. written com- Conglomerate. The Mission Valley Formation is the munication, 1971). continuum and regressive equivalent of the Scripps 4) Foraminifera have been collected from the Ar- Formation (figure 4). dath Shale. Scripps Formation, Friars Formation, A final regressive conglomerate unit, the and Stadium Conglomerate. The fauna from the Pomerado Conglomerate (figure 4), has been preser- stratlgraphically uppermost part of the section has ved high in the stratigraphic succession. One short been reported by Mallory (1959) to be correlative period transgression marked by the Miramar tongue with his Narizian Stage (late Eocene age) and that near the Miramar Reservoir in the Poway from the lower part of the section with his Ulatlsian Stage (middle Eocene age). Stelneck and Gibson quadrangle is the uppermost marine sandstone of (1971) have studied Foraminifera from both the Ar- the column. dath Shale and Stadium Conglomerate and report a middle Eocene and late middle Eocene age respectively.

The discussion that follows establishes the EOCENE BIOSTRATIGRAPHY fossil composition of each of the nine lithostratigraphic units within the Eocene San Diego The Eocene lithostratigraphic succession embayment and relates the West Coast (California) discussed in the preceding pages contains fossil molluscan stages to the North American Mammal organisms representative of deep water marine, lit- Ages and these two chronologies to the Eocene of toral marine, lagoonal, and nonmarine fluviatile en- Europe by way of correlations based on planktonic vironments. These fossils together indicate that the calcareous nannoplankton zones. boundary between the middle and late Eocene lies A relatively rich molluscan assemblage has lies near the boundary between the La Jolla and been collected from the middle part of the Mount

Poway Groups in the central exposed part of the San Soledad Formation at localities I and 2 (figure 7; Diego embayment and that the middle and late (plates 2A, 3A). These localities combined are repre-

Eocene boundary falls within the Uintan Mammal sented by M I in figure 6. The assemblage from these Age (Golz and Kennedy, 1971). This is later, localities includes TurriiclUi iivasana iippliniw Hanna, relative to the base of the Uintan, than originally Ficopsis coopcriiina Stewart, and Tejonia lajollacnsis proposed (Wood et al.. 1941). The Eocene suc- (Stewart), all of which are restricted to the middle cession of the San Diego embayment is presently the Eocene Domengine Stage of California (Givens, only place known in North America where this part 1974). 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 23

GEOLOGIC COLUMN 24 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

Figure 7. Index map of fossil mollusk localities. (See plates 1A-3A and plate 2B (Kennedy and Peterson. 1975) for detailed locations.] 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 25

Figure 8. Index map of fossil calcareous nannoplankton localities. (See plates 1A, 2A and plate 2B, 3B (Kennedy and Peterson, 1975) for detailed locations.) BULL. 200 26 CALIFORNIA DIVISION OF MINES AND GEOLOGY

^LACM 65190 UCMP V687I vUCMP V6893

and Peterson, 1975) for detailed locations.) Figure 9. Index map of fossil mammal localities. (See plates 1A. 2A and plate 3B (Kennedy 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 27

Fossil mollusks, calcareous nannoplankton, its type section at locality I 7 (figure 7; plate 1 A) in- mammals, and Foraminifera have been collected cludes Turritella andersoni lawsoni Dickerson, from the Ardath Shale. The molluscan fauna was Turritella uvasana applinae Hanna, Tejonia lajollaensis collected from localities 6 through 16 (figure 7; (Stewart), and Ficopsis cooperiana Stewart. These plates lA,2A).The localities combined are indicated fossils together indicate a Domengine Age (Givens, by M3 in figure 6. The calcareous nannoplankton 1974). An assemblage from locality 25 (figure 7; flora was collected from localities 1 through 1 1 plate 2A) 20 m below the contact between the Scripps

1 These localities combined are Formation and the overlying Friars Formation about (figure 8 ; plates A, 2A). indicated by Nl in figure 6. Fossil mammals have 400 m west of the type section of the Friars includes been collected from Los Angeles County Museum Nekewis io (Gabb) and Ectinochilus conalifer localities LACM 6673, LACM (CIT) 456, and supraplicatus (Gabb). The upper part of the Scripps LACM 1401 and from the University of California, Formation based on the co-occurrence of these Berkeley, locality UCMP V6884 (figure 9; plates 1 A, species is considered to belong to the "Transition 2A). These localities are combined in figure 6 as Stage" and to be middle or late Eocene in age (C. R. VI. Foraminifera have been collected from the Givens, written communication, 1973). Ardath Shale at a locality 1.5 km north of its type The Scripps Formation is in part laterally section in Rose Canyon (Steineck and Gibson, 1 971 ). equivalent to and in part conformably overlain by This locality is indicated by Fl in figure 6. rocks of the Friars Formation. Mollusks were The molluscan assemblage collected includes collected within the Friars Formation from near the Turritella uvasana applinae Hanna, f(copii.9 cooperiana gradational boundary with the underlying Scripps Stewart, and Tejonia lajollaensis (Stewart), all of Formation at localities 26 and 27 (figure 7; plate 2A). which are restricted to the Domengine Stage of These localities, combined because of their close California (Givens, 1974). Calcareous nan- stratigraphic proximity to locality 24 and 25, also noplankton from localities 6 through 9 occur at the are indicated by M5 in figure 6. The mammal fauna same stratigraphic interval as mollusks from was collected from seven localities in the Mission localities 10 and 11. Nannoplankton locality 9 Valley-Mission Gorge region. These include the localities (figure 8;plate 2A), locality L 1 3 of Bukry and Ken- University of California, Riverside, UCR nedy (1969), yields fossils indicative of an early RV 7046, RV 67112, RV 7047, RV 7049, RV middle Eocene age (Discoaster sublodoensis zone). 7050, RV 68151, and RV 68152; University of These include Coccolithus eopelagicus (Bram\ene and California, Berkeley, localities UCMP V6872, V Riedel), Coccolithus pelagicus (Wallich), Helicopon- 6873, and V6888; and Los Angeles County Museum tospaera seminulum lophota (Bramlette and Sullivan), localities LACM (CIT) 250 and 314 (figure 9; Discoaster distinctus Martini, and Discoaster bar- Kennedy and Peterson, 1975, plate 38 ). These hadiensis Tan. Calcareous nannoplankton, also of localities together are indicated by V2 in figure 6. early middle Eocene age {Discoaster sublodoensis The molluscan fauna collected includes Nekewis zone), were collected from locality 1 1 (figure 8; io (Gabb) and Ectinochilus canalifer supraplicatus plate 2A) in Rose Canyon from the type section of (Gabb). These species together suggest that the Hanna's (1926) Rose Canyon Shale Member. lower part of the Friars Formation belongs to the Steineck and Gibson (1971, p. 477) collected from "Transition Stage" and is middle and late Eocene in

this same locality and reported that the "occurrence age (Givens, 1 974). of Subhotina patagonica Todd in both the Rose The mammalian fauna collected from the Friars Shale and Cozy Dell Formation suggests Canyon Formation has been studied by Golz (1973). He time-equivalence of the two units (early middle reports that the stage of evolution of the artiodactyl Eocene in age)." fauna from the Friars Formation in the upper The fossil mammals collected from the Ardath Tecolote Creek and Mission Valley-Mission Gorge Shale have been reported by Golz (1973) to be of area is indicative of Uinta B Age. However, since these Uinta A or Bridgerian Age. Fossil calcareous nannoplankton, mammals, a marine land animals were transported to and planktonic Foraminifera have been collected environment, it is possible that they are depositionai from the Stadium Conglomerate. The nannoplankton the early middle Eocene rocks in which older than were collected from a siltstone interbed at locality they lie. 14 (figure 8;plate 3B, Kennedy and Peterson, 1 975) The Ardath Shale is conformably and near the intersection of Murphy Canyon and gradationally overlain by richly fossiliferous rocks Mission Valley. This locality is indicated as N2 in of the Scripps Formation. Fossil mollusks were figure 6. The mammalian fauna was collected from collected within the stratigraphically lower and in- Los Angeles County Museum locality LACM 1723 termediate part of the Scripps Formation from and from University of California, Berkeley, locality

localities 17 through 23 (figure 7; plates 1 A, 2A) and UCMP V6840(figure9; plate3B, Kennedy and Peter- are indicated together as M4 in figure 6. Mollusks son, 1975). Together these localities are indicated were also collected from the upper part of the as V3 in figure 6. The Foraminifera were collected Scripps Formation near its contact with the Friars from nannoplankton locality 14 by Steineck and Formation at localities 24 and 25 (figure 7; plate 2A) Gibson (1971). This locality is indicated as F2 in and are indicated together as M5 in figure 6. figure 6. A molluscan assemblage from a conglomerate The nannofossils collected include at the base of the Scripps Formation 400 m north of Reticulofenestra umbilica (Levin) and Discoaster 28 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

tlistinctus Martini. Because Reticulofenestra umbilica Eocene age has been assigned to the Pomerado ranges trom the upper middle Eocene to lower Conglomerate at its type locality on the basis of its Oligocene, the age of these samples based on nan- superpositional and gradational relationship with not'ossils is questionable. the underlying fossiliferous Mission Valley For- The mammalian fauna, which occurs mation at its type locality. siratigraphically higher and to the east of the marine The biostratigraphic relationship between fossil fauna and flora,,has been correlated with the Uinta B mollusks, calcareous nannoplankton, Foraminifera, or low Uinta C (Golz, 1973). and mammals with respect to the lithostratigraphy Foraminifera from the Murphy Canyon locality of the Eocene San Diego embayment is illustrated in include Cloborotaloides stiieri Bolli and Trun- figure 6. As discussed in the preceding pages, each coroialoides coUacteus Finlay (Steineck and Gibson, of the fossil localities shown in figure 6 is a composite of many field localities that occur at or very 1971, p. 478). Though Steineck and Gibson state that this "co-occurrence suggests equivalence with near the same stratigraphic horizon. These com- upper middle Eocene strata", Jenkins (1965, figure posite localities have been plotted with respect to their relative vertical 2) considers that the occurrence of these two and horizontal stratigraphic species indicates a restricted upper Eocene age. The position within the lithostratigraphic regime. The foraminiferal assemblage collected from the Stadium boundaries and postulated interrelationships of the Conglomerate lies near the boundary between the West Coast (California) Marine Stages. European middle and upper Eocene based upon the coccolith Stages, Epochs, Series, and absolute (radiometric) time scale in millions of years are also shown. assemblage with which it is interbedded.

The Stadium Conglomerate is conformably Composite mollusk locality M5 and composite overlain by richly fossiliferous strata of the Mission mammal locality V2 lie within a few meters of the Valley Formation. The fossils include mollusks, same stratigraphic level and are considered to be calcareous nannoplankton, and mammals. The correlative in age. The molluscan fauna belongs to mollusks were collected from localities 28 through the "Transition Stage" and the mammalian fauna to the Uinta B Mammal Age of North America. 33 (figure 7;plate2A; and plate 2B , Kennedy and Peterson, 1975). These localities combined are in- Similarly, composite mollusk locality M6 and mam- dicated by M6 in figure 6. The fossil nannoplankton mal locality V4 lie at the same stratigraphic interval. were collected from locality 15 (figure 8; plate 2B, These are Tejon and Uinta C in age respectively. Kennedy and Peterson, 1975). This locality is Givens (1974) has correlated the Tejon Stage of the shown by N3 in figure 6. The fossil mammals have southern California Ventura Basin with the upper been collected from University of California, River- Eocene of Europe, on the basis of species also side, locality UCR RV 7048, University of Califor- reported here from composite locality M6. The nia, Berkeley, locality UCMP V6871 and Los calcareous nannoplankton from composite locality Angeles County Museum locality LACM 65190 N3 which lies at the same stratigraphic interval as (figure 9; plate 3B, Kennedy and Peterson, 1975). locality M6, are also suggestive of a late Eocene age. Together these localities are indicated as V4 in Calcareous nannoplankton from composite figure 6. fossil locality Nl within the middle part of the Ar- The molluscan fauna collected from localities dath Shale have been correlated with the Discoasier 28 through 32 include Tellina tehachapii Anderson siiblodoensis zone (Bukry and Kennedy, 1969). The and Hanna, Matroccillisia undersoni Dickerson, and flora of this zone has previously been reported from Crassdtellii uvusuna s. s. Gabb. These species when the Canoas Siltstone Member of the Kreyenhagen considered together are characteristic of the upper Formation on Garza Creek near Oil City, California; Eocene Tejon Stage of California (Givens, 1974). from the middle Lutetian strata at Gibret, France; Mollusks collected from locality 33 which is ap- and from the Lutetian strata of the Paris basin in proximately 25 m stratigraphically higher in the sec- France (Bouche, 1962). lion than locality include Tiirritella uvasana 28 The fossil molluscan assemblage collected from siiri^eanti (Anderson and Hanna) which Givens composite locality M5 is indicative of the "Tran- to the part of the (1973) considers restricted upper sition Stage". Givens (1974) has shown that the Tejon Stage. "Transition Stage" of southern California, as The calcareous nannoplankton flora collected originally defined by Clark and Vokes (1936), from locality 15 is sparse but includes several overlaps the middle-upper Eocene boundary as distinctive species including Reticulofenesiru iim- established in the same strata by planktonic hilica (Levin) and Discoaswr distinctus Martini, which correlations with type Eocene strata in Europe. together suggest either a late middle Eocene or early Composite locality V2 also lies at the same Eocene age. stratigraphic interval at locality M5 and is therefore The artiodactyl fauna collected from the considered to likewise lie near the middle upper Mission Valley Formation has been reported by Eocene boundary. The fossils from composite Golz (1973) to belong to a stage of evolution localities F2 and N2 are stratigraphically higher correlative with the Uinta C. than those from localities M5 and V2 and are con- The Mission Valley Formation is conformably sidered to he from rocks that are at least late middle overlain by rocks of the Pomerado Conglomerate Eocene age. The fossils from composite localities

and no fossils have been found in these rocks. A late M3, VI , and Fl lie at the same stratigraphic interval 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 29

as those from Nl and are, therefore, also middle Miocene-Pliocene Rosarito Beach Formation in Eocene in age. northern Baja California. The cobble conglomerate In conclusion, composite localities N3, M6, and beds are composed primarily of Poway-type clasts, V4 lie within the Mission Valley Formation and are but some beds contain up to 50 percent clasts of late Eocene in age. Composite localities Nl, M3, granitic and meiavolcanic rocks derived from the local basement complex. The bentonite is light Fl , and VI lie within the Ardath Shale and are middle Eocene in age. The boundary between the mid- brown, waxy to earthy, expansible, and very soft. dle and late Eocene lies intermediate between these The San Diego Formation rests unconformably two units within parts of the Scripps Formation, on the older pre-Pliocene rocks and is overlain by Friars Formation, and Stadium Conglomerate. 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. POST-EOCENE DEPOSITS Lindavista Formation Miocene The Lindavista Formation was named by Hanna (1926) for exposures at the Lindavista railroad Andesite Dike siding in the La Jolla quadrangle (Lat 32° 53' N.; andesite dike is located approximately 600 m 7° An Long 1 1 1 r W.). The formation consists of near- north of the Scripps Institution of Oceanography shore marine and nonmarine sediments deposited pier(plate 2A).The rock is black, fine grained, and on a 10 kilometer-wide wave-cut platform (Lin- has flow structures and columnar joints. The dike davista Terrace of Hanna, 1926) following the strikes approximately N. 45° E., but its intersection deposition of the middle or late Pliocene San Diego with Eocene rock in the sea cliff cannot be seen. The Formation (Hertlein and Grant, 1944) and prior to dike has been observed by scuba diving to extend the deposition of the fossiliferous late Pleistocene from the beach directly beneath the U.S. Fishery (Sangamon) Bay Point Formation (Kern, 1971). A Oceanography Center for a distance of ap- molluscan fauna from the Lindavista Formation, in- proximately 400 m to the southwest (W. Reetz, per- cluding the extinct species Pecten bellus. not known sonal communication, 1971). A whole-rock from the late Pleistocene, suggests an early potassium-argon analysis of this rock, which shows Pleistocene or late Pliocene age for these rocks (G. some evidence of wall-rock assimilation, gave an age Kennedy, 1973). The Lindavista Formation is of 10.9±1.1 million years (J.W. Hawkins, personal predominantly composed of moderate reddish- communication, 1970). 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 Pliocene and Pleistocene of the Lindavista Formation have been largely derived from the older sedimentary rocks within the Pliocene and Pleistocene rocks include marine San Diego embayment. Where iron staining, so com- sandstone and conglomerate of the upper Pliocene mon to the Lindavista Formation, extends down- San Diego Formation, marine and nonmarine sand- ward into the underlying Eocene rocks, the two stone of the lower Pleistocene Lindavista For- become difficult to differentiate. mation, and lagoonal and nonmarine sandstone of the upper Pleistocene Bay Point Formation. Bay Point Fornnation San Diego Fornnation The Bay Point Formation (Hertlein and Grant, 1939) is widespread and well exposed in the area The San Diego Formation (Dall, 1898) is mid- adjacent to the present-day coastline. It is composed dle or late Pliocene in age (Hertlein and Grant, mostly of marine and nonmarine, poorly con- 1 944; Cleveland, 1 960). It crops out from the lower solidated, fine- and medium-grained, pale brown, south-facing slopes of Mount Soledad at Pacific fossiliferous sandstone. Beach south to near San Diego Civic Center and along the north-facing slopes of Mission Valley The fossils found occur between and 30 m from near Old Town to the eastern boundary of the above mean high tide and include mollusks, area. These exposures, attaining a maximum Foraminifera, and ostracods. These together in- thickness of 30 m, are composed of yellowish- dicate a brackish water estuarine depositional en- brown, fine- to medium-grained, poorly indurated vironment and a late Pleistocene (Sangamon) age sandstone. Cobble conglomerate, thin beds of ben- (Kern, 1971). tonite, marl, and brown mudstone further charac- The marine part of the Bay Point Formation in- terize the section. The thickness of the San Diego terfingers with unfossiliferous sandstone that lies Formation increases markedly to the south, where it generally more than 30 m but less than 60 m above has been reported to attain a maximum thickness of sea level. This part of the Bay Point Formation is 400 m (Hertlein and Grant, 1939). The lower 200 m considered to be nonmarine slope wash; however, it of this section correlates to the south with the has not been differentiated on the geologic map. 30 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

Pleistocene and Holocene of failure can be avoided. Landslide incidence in the Surficial Deposits area is greatly increased during periods of high an- nual rainfall; good subdrainage may be another means of control. During periods of high The Pleistocene and Holocene surficial precipitation, the saturation of bedrock may result deposits are detrital materials which include in the lowering of the internal strength of perhaps stream-terrace, landslide, alluvium, slope wash, and already weak rock. Removal of slope-supporting beach deposits and artificially compacted fill. material might then increase landslide potential. The landslide deposits of the area can be sub- Stream-Terrace Deposits divided into tlve major groups based on lithology Stream-terrace deposits occur very locally as and genesis. These are (1 )rotational slump deposits thin veneer along the larger drainage courses. The associated with the shallow stream channels un- deposits include unconsolidated sand and gravel derlain by sedimentary rocks of Eocene age (photo derived from older sedimentary, igneous, and 3);(2)rotational slump deposits associated with the metamorphic rocks. sea cliffs underlain by sedimentary rocks of Eocene age north of the Rose Canyon fault zone (photo 4); Landslide Deposits I (3) rotational slump deposits associated with The study area is underlain in large part by in- sedimentary rocks of Upper Cretaceous and Eocene competent sedimentary rocks which have been age within the Rose Canyon fault zone (photo 5);(4) broadly dissected by shallow westward-flowing rotational slump deposits associated with sedimen- stream channels. Most of the landslides in the map tary rocks of Upper Cretaceous age on the east- area are rotational slumps and have occurred along facing slopes of the Point Loma Peninsula (photos 6 valley walls where rocks of the Delmar, Friars, and Mission Valley Formations crop out. Slope stability with respect to potential landsliding 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 bedding, 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 conditions of drainage. The landslides are gravity slides resulting from basal erosion of oversieepened slopes, ground water saturation, surface-water erosion, and poorly consolidated rock. Sliding has generally occurred along a multiple slip surface associated with expansible clay The slides have consistently maintained internal homogeneity, and rotation of the slide mass is normally less than five degrees. Subsurface Photo 3. A small slump that has occurred within the Ardath examination of these slides was beyond the scope of Shale as a result of slope undercutting and incompetent rocks, looking southeast. 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 **'Z'A north-facing slopes commonly stand 10 to 15 ,^^^^^^:i degrees steeper than the south-facing ones, which -i*'^^^^^ seldom reach angles greater than 30 degrees. Over- ^^^^^l^p^r^^-^^^ steepening of the stream channels is controlled in part by the presence of resistant impermeable rock layers exposed along the upper slopes as erosional -"^i:- 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 m claystone of the Delmar, Friars, and Mission Valley Photo 4. Torrey Pines State Park landslide, looking east. The landslide is located 2400 meters south ol Soledad Valley in the Formations just as in most of the natural slides. sea cliffs. The slide mass is composed of incompetent rocks Stability filling (compacted till placed over a ben- that are of Eocene age and belong to the Delmar Formation, ched cut slope) may be one means by which this type Torrey Sandstone, and Ardath Shale. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 31

and 7); (5) rockfall deposits associated with The stated median particle size was taken from sedimentary rocks of Upper Cretaceous and ihe 50 percent cumulative level of particle size Pleistocene age in the sea cliffs between the Rose distribution graphs. The arithmetic mean of the Canyon fault zone and the tip of Point Loma Penin- median particle sizes among all the samples is 0.016 sula (photo 8; Kennedy, 1973b). mm (16 microns), which is in the lower portion of Eighteen clay samples were collected from for- the silt range. mations that have high landslide incidence. These Associations between plasticity index, particle samples were analyzed for their particle size size, and the percentage of clay-sized particles are distribution, clay mineral content, and Atterberg readily observed from the data of table 1. The limits. medium-plasticity samples (PI = 10 to 20) have an average median particle size of 47 microns. High- Table 1 presents the results of the Atterberg plasticity samples (PI = 20 to 40) have an average tests and the quantity of the individual size fractions particle size of 14 microns. The very-high- from the particle size distribution tests. median plasticity samples (PI > 40) have a mean particle For engineering purposes the clay fraction is size of 6 microns. defined as less than 0.002 millimeter (mm), the silt landslides have occurred in rocks that fraction from 0.002 to 0.074 mm, and the sand frac- Most have a plasticity index greater than 20. Surficial tion from 0.074 to 2.0 millimeters. The liquid limit slumping of slopes underlain by rocks of the Delmar (LL) is defined as the minimum moisture content at and Friars Formations and Ardath Shale is most which the material behaves as a liquid using this abundant where the plasticity index is greater than lest. The plastic limit (PL) is defined as the 35. Expansion cracks are especially well developed minimum moisture content at which the sample and to 50 centimeters (cm) deep and 5-10 cm behaves plastically using this specified test up wide in much of the area underlain by the Delmar procedure. The plasticity index (PI) is the numerical Friars Formations where the plastic index is difference between the liquid limit and the plastic and greater than 40. 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" (Terzaghi and Peck, 1968), whereas an inverse relationship exists between the plasticity index and "shear resistance."

TRACE OF THE MOUNT SOLEDAD FAULT LANDSLIDE " DEPOSITS

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 Photo 7. Fort Rosecrans landslide on Point Loma Peninsula, oversteepened slopes associated with an erosional looking west. This slide mass Is presently moving toward the scarp, looking southeast along the Mount Soledad fault. east at a rate of approximately 10 centimeters per year. 32 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

"o 1:1 * = C M i>"-..2_oS^ S o Sj S^l u * 2 ;; ^*^ > S — T) J "^3 "^ "S O M O M o c »j o - - • - e ^^-" i •5 3-^ O 3 U ^»* O.S O -—JO •a (U . ^- S « O S o — §-5 J. „ > >- . = °Z-z T3 5>- .i 3l' a. "1,^ - «•- rt = "< fe — >fM 2 o, OrXsS 2§« o-'.*. E 3 - M 3 «— Cr^ - Oi/^

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° c „ 2-2 " _>. C t^ f« k o S >i; 2 " O o«> ° g.2!b £5=;.= i I' 8> g2a^ ft, J3^ S «(-%> o ;iQ-S5

" E 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 33 34 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 35

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

Alluvium and Slope Wash Artificially Compacted Fill

Alluvium consists primarily of poorly con- Artificial fill consists of artificially compacted solidated stream deposits of silt, sand, and cobble- earth materials derived from many sources. Only sized particles derived from bedrock sources that lie large areas underlain by artificial fill have been within or near the area. These deposits intertongue delineated on the geologic maps. 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 STRUCTURE surficial materials derived chiefly from nearby soil AND SEISMIC HISTORY and decomposed bedrock sources. The slope wash is deposited along the flanks of the lower valley r--

slopes by the actions of gravity and surface water. I Faults in the San Diego coasial area lie within a Thick deposits of slope wash are especially common regional northwest-striking right-lateral fault system on the Delmar Formation, Ardath Shale, Scripps that includes the active Mission Creek, San An- j

Formation, and Friars Formation where deep soil I dreas, San Jacinto, and Elsinore fault zones to the horizons have developed. Expansive clay materials east and the Agua Blanca, San Clemente, and Ram- deposited as slope wash yield the hummocky part fault zones to the west. Within the study area topography developed on rocks of lagoonal and non- the faults comprise two prominent sets. One set marine origin. strikes parallel to the regional grain, whereas the other set strikes northeast. Faults belonging to both Beach Deposits of these sets have displaced rocks of the late The beach deposits are composed of un- Pleistocene Bay Point Formation which has, on the consolidated sand and silt. They mantle those parts basis of a rich nearshore molluscan fauna, been of the present day sea coast where erosional con- assigned an age of approximately 100,000 years ditions are slow. They are derived from many sour- (Kern, 1971). ces as a result of longshore drift and alluvial The most prominent faults within the northwest discharge from the major stream courses. striking set belong to the Rose Canyon fault zone. 36 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

These faults juxtapose nearly flat-lying Eocene, In the northern coastal part of the area at Pliocene, and Pleistocene rocks with steeply tilted Torrey Pines State Park and in the southern part of Upper Cretaceous and Eocene rocks. The Rose the area at Point Loma, the structural grain of the Canyon fault has been considered a southern ex- area is nearly perpendicular to the Rose Canyon tension of the Nevvport-Inglewood fault zone fault zone. The average strike of the grain is 30 to (Corey, 1954; Emery, 1960; King, 1969; Moore, 40 degrees east of north. The separation along most

1972) and a northern extension of both the Los of the faults is vertical and ranges from 1 cm to 100 Buenos and the San Miguel faults (Wiegand, 1970; m. Moore and Kennedy, 1970; Moore, 1972). If the Several northeast striking faults displace Rose Canyon-Los Buenos fault zone is continuous, Pleistocene and younger(?) deposits. The Carmel

it has an onshore length of 65 km and extends from Valley fault south of Del Mar (plate lA) has ap- La Jolla on the north to near El Rosarila in northern proximately 2 m of vertical separation, involving the Baja California on the south. If the Rose Canyon Lindavista Formation at lat 32° 55' 10" N.; long fault zone is continuous with the San Miguel fault, 117° 14' 50" W. Along this same fault at lat 32° 55' the onshore length of this segment is over 250 km 20" N.; long 117° 14' 50" W., the late Pleistocene and extends from La Jolla on the north to near San Bay Point Formation has been tilted approximately Miguel in northern Baja California on the south. 10 degrees. It is speculated, however, that at least The mapped northern offshore extension of the part of this dip is initial and related to its Rose Canyon fault zone extends from La Jolla to deposition. A small fault on the east side of the within 45 km of the southern onshore termination of Point Loma Peninsula, located at lat 32° 40' 40" N.;

the Newport-Inglewood fault zone (Moore, 1972). long 1 17° 14' 15" W., also displaces rocks of the Point Loma and Mount Soledad are fault blocks that Bay Point Formation. The separation on this fault is were uplifted along the Rose Canyon fault zone in dip-slip and on the order of 3 meters. The Bay Point part after the deposition of the Lindavista For- Formation is also faulted by a small northeast mation. At least 135 m of vertical separation can be striking fault that intersects the Point Loma fault at measured in the vicinity of Mount Soledad and La an oblique angle(plate3A).The vertical separation of Jolla (plate 2A). The direction of the vertical the Bay Point Formation related to this fault and the movement at La Jolla is west side up, whereas at Point Loma fault together is in excess of 30 meters. Mission Bay it is west side down (sections B-B', C- The possibility of Holocene fault activity in the

C). At least 1 00 m of separation has been shown on area is not ruled out, though no direct field evidence the Rose Canyon fault zone in the Mission Bay area supports this fact. Holocene faulting is indirectly with the west side down (Peterson, 1970). Possibly postulated by the fact that historic seismicity might the Mount Soledad block rotated along an axis nor- be related to faulting on the Rose Canyon fault zone mal to the strike of the fault zone thereby elevating in the San Diego Bay area and by subbottom Mount Soledad along the northwest side of the zone acoustic profiles that show probable Holocene and sinking Mission Bay along the southwest side. sediments offset on the sea floor at a point ap- This tilted block model is supported by the fact that proximately 25 km north of La Jolla along the trace a 30 m high wave-cut platform upon which the Lin- of the Rose Canyon fault (Moore. 1972). davista Formation originally was deposited, on the Forty-four earthquakes of Richter magnitude south-facing slopes of Mount Soledad, is inclined to 2.5 to 3.7 (M 2.5-3.7) have been recorded within the the south and extends nearly continuously from an greater San Diego area by the California Institute of elevation of over 250 m at the north to near sea level Technology Seismological Laboratory since 1950. at the south. Three of these which occurred in the vicinity of San Steep folds associated with the nor- Diego BayonJune21 and22andJuly 14, 1964, had theasternmost part of the Mount Soledad block (sec- epicenter localities within a few kilometers of San tion B-B') are considered to be in part the result of Diego and magnitudes of 3.7, 3.6, and 3.5, respec- compression developed by strike-slip movement. tively. The rotation of Mount Soledad was questionably In addition to earthquakes originating in the San caused by flexure associated with the change in Diego area, ground shaking has been felt there strike of the Rose Canyon and Mount Soledad faults initiated by earthquakes that have had epicenters up between LaJollaCove and Rose Canyon (plate 2A). to 100 km away. Several of these earthquakes have The Tertiary and younger rocks that lie immediately caused damage in San Diego and are worthy of men- west of the fault zone are not deformed and they tion. make a strike-slip model and compressional folding The 1933 Long Beach earthquake (M 6.6) logical. It has been suggested that the Rose Canyon caused minor damage throughout northwestern San fault is part of a regional right-lateral strike-slip Diego County and was felt sharply as far south as fault system. The distribution of the San Diego For- San Diego. The epicenter is shown by the California mation along the Rose Canyon fault zone between Institute of Technology Seismological Laboratory to Pacific Beach and Tecolote Canyon(plate 2A) is in- have been south of Long Beach along the inferred terpreted as resulting from 4 km of right-lateral trace of the Newport-Inglewood fault zone. strike-slip motion on the Rose Canyon fault. On November 4, 1949. and on February 9, Horizontal slickensides measured on the Rose 1956, earthquakes felt sharply in San Diego oc- Canyon fault at La Jolla and Mount Soledad further curred on the Valecitos-San Miguel fault in northern suggest strike-slip faulting. Baja California. The 1949 earthquake (M 5.7) had 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 37

an epicentral distance of approximately 75 km these— the 1940 Imperial Valley earthquake (M southeast of the San Diego Civic Center. The 7.1), the 1951 Superstition Hills earthquake (M epicenter of the 1956 earthquake (M 6.8) was ap- 5.6), and the 1968 Borrego Mountain earthquake (M proximately 1 75 km south of San Diego. Three af- 6.5)—caused minor damage to structures in the San tershocks of this earthquake, with magnitudes Diego coastal area and initiated landsliding of sea greater than 6, occurred in 1956 on February 9, 14, cliff property at Point Loma, La Jolla, and Torrey and 15. Ground rupture of 20 km was associated Pines State Park (Kennedy, 1973). with this earthquake in the vicinity of the epicenter The February 9, 1971, San Fernando earth- (Shor and Roberts, 1958). quake (M 6.4) was felt sharply throughout the Several earthquakes (M > 5) have been recor- southern California coastal area. The intensity of ded on the Agua Blanca fault in northern Baja the earthquake at San Diego was V (Scott, 1971 ) on California during the past 30 years with epicentral the Modified Mercalli scale. Minor damage was distances within 125 km of San Diego. Holocene reported as far south as the Mexican border, and fault scarps in the area between Ensenada and Santo two small landslides occurred at Sunset Cliffs as a Tomas suggest surface rupture has occurred in at direct result of the initial shock. least the past few thousand years. Allen et al. (1965) show a strain release ofO.25 During the past 35 years, earthquakes located to 4 (M 3) earthquakes/100 km2 for the 29-year in the Imperial Valley and Salton Trough area were period between 1934 and 1963 for the San Diego felt in western San Diego County. Three of area. 38 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

REFERENCES CITED

Allen. C.R.. et al., 1965, Relationship between selsmlclty and Golz, D.J., and Kennedy, MP. 1971, Comparison of Mammalian geologic structure In the southern Calitornia region: and Invertebrate Chronologies in the Eocene of southern Seismologlcal Soc of America Bull., v. 55, no. 4, p. 753-797. California: Geol. Soc. America Abstracts with Program, v 6. p. 125. Allison. E.C.. 1964. Geology o( areas bordering Gulf of Califor- 3- nia: American Assoc. Petroleum Geologists f^em 3, p. Gray, C.H., Jr . Kennedy, MP., and Morton, P K., 1971, Petroleum 29. potential of southern coastal and mountain area, Califor- nia: American Assoc Petroleum Geologists, Mem. 15, p. Beal. CM.. 1924, Informe sobre la exploracion geologica de la 372-383. Baja California: Boletin Petroleo. v. 17, p. 417-473. Hanna. M.A., 1926, Geology of the La Jolla quadrangle, Califor- Berggren, W.A., 1969, Rates of evolution in some Cenozoic nia: University of California, Dept. Geol. Sci. Bull., v. 16, p. planktonic Foraminifera: Micropaleo, v. 15, no. 3. 187-246.

Bouche, P.M., 1962. Nannofossiles calcaires du Lutetien du Hertlein, L.G., and Grant. U.S.. IV, 1939. Geology and oil bassin de Paris: Rev. f\^icropaleontologie, v 5. p. 75-103. possibilities of southwestern San Diego County: California Jour Mines and Geol., v. 35, p. 57-78. Bukry. David, and Kennedy. MP.. 1969, Cretaceous and Eocene coccoliths at San Diego. California, in Short contributions to Hertlein, L.G., and Grant, U.S., IV, 1944, The geology and California geology California Division of Mines and Geology paleontology of the marine Pliocene of San Diego, Califor- Special Report 100, p. 33-43. nia, pt. 1, Geology: San Diego Soc. Nat History Mem., v 2, p. 1-72. Bushee, J., Holden, J., Geyer, B., and Gastil, G., 1963, Lead- for of southwestern alpha dates some basement rocks Jenkins, D.G , 1965. Planktonic Foraminiferal Zones and New California: Geol. Soc. America Bull., v. 74. p. 803-806. Taxa from the Danian to lower Miocene of New Zealand: New Zealand Jour. Geol. Geophys., v. 8, p. 1088-1126. Clark. B.L.. and Vokes, HE.. 1936, Summary of marine Eocene sequence of western North America: Geol. Soc. America Kennedy, G.L., 1973, Early Pleistocene Invertebrate Faunule Bull.. V. 47. p. 851-876, 2 pIs., 3 figs. from the Lindavista Formation, San Diego, California: San Diego Soc. Nat. History Transactions, v. 17, p. 119-128. Cleveland. G.B.. 1960. Geology of the Otay clay deposit, San Diego County, California: California Div. Mines Spec. Rept. Kennedy, M.P., 1967, Preliminary report, engineering geology of 16. 64, p. the city of San Diego, California: California Div. of Mines and Geology open tile, 21 p., 3 maps, scale 1:24,000. Corey, W.H., 1954. Tertiary basins of southern California, in Geol. of southern California: California Div. Mines Bull. 170, Kennedy. MP. 1969, Preliminary geologic maps of portions of chpt. p. 73-83. 3, San Diego city. California: California Division of Mines and Geology open file reports 69-1 (Del Mar sheet). 68-10 (Del Dall, W.H., 1898, 18th Ann. Rept. U.S. Geol. Survey, pt. 2. Mar - La Jolla sheet), 69-13 (La Jolla - Point Loma sheet), correlation table opp. p. 334. 69-14 (Point Loma sheet), scale 1:9,6000.

DeLisle, M., Morgan. J, R., Heldenbrand, J., and Gastil, G., 1965, Kennedy. MP.. 1971, Eocene shoreline fades in the San Diego Lead-alpha ages and possible sources of metavolcanic coastal area, California: Geol, Soc. America Abstracts with rock clasts in the Poway Conglomerate, southwest Califor- Program, v. 6 p. 142. nia: Geol. Soc. America Bull., v. 76, p. 1069-1074.

Kennedy, MP., 1973a, Stratigraphy of the San Diego em- Ellis. A.J.. 1919, Geology, western part of San Diego County, bayment, California: Unpublished Ph.D. dissertation, California: U.S. Geol. Survey Water-Supply Paper 446, p. 50- University of California, Riverside. 76.

Emery. K.O.. 1960, The sea off southern California, a modern Kennedy, MP., 1973b, Sea cliff erosion at Sunset Cliffs, San Div. habitat of petroleum; New York, London, John Wiley, 366 p., Diego, California: California Mines and Geology, map. California Geology, v. 26, p. 27-31.

Evernden, J,F.. and Kistler. R.W.. 1970, Chronology of em- Kennedy, M.P., and Moore, G.W., 1971a, Stratigraphic relations placement of Mesozoic batholithic complexes in California of upper Cretaceous and Eocene formations, San Diego and western Nevada: Geol. Survey Prof. Paper 623. 42 U.S. coastal area, California: American Assoc. Petroleum P Geologists Bull., v. 55, p. 709-722.

Fife, D.L., Minch, J. A., and Crampton. P.J., 1967, Late Jurassic Age of the Santiago Peak Volcanics, California: Geol. Soc. Kennedy. MP., and Moore, G.W.. 1971b. Stratigraphy and struc- America Bull., v. 78, p. 299-304. ture of the area between Oceanside and San Diego, California: geologic road log, in Elders W.A.. ed., 1971, Geological excursions in southern California: Geol. Soc, Flynn, C.J . 1970. Post-batholithic geology of the La Gloria- Press Rodriguez area, Baja California, Mexico: Geol. Soc. America Cordilleran Section Meeting, Riverside, California, America Bull., v. 81, p. 1789-1806. field trip guidebook.

Givens, C.R., 1974, Eocene Molluscan biostratigraphy of the Kennedy, MP., and Peterson, G.L., 1975, Geology of the La Pine Mountain area, Ventura County, California: University Mesa, Poway. and SW 1/4 Escondido quadrangles, eastern of California, Dept. Geol. Sci. Bull., v. 109. 107 p. San Diego metropolitan area, California: California Div. Mines and Geology Bull. 200B. Golz, D.J., 1971, SelenodonI Artiodactyls from the Eocene of southern California: Geol Soc. America Abstracts with Kern, J. P., 1971, Paleoenvironmental analysis of a late Program, v. 6, p. 125. Pleistocene estuary in southern California: Journal Paleo.. V. 45, p. 810-823. Golz, D.J., 1973, The Eocene Artiodactyla of southern Califor- nia: Unpublished Ph.D. dissertation. University of Califor- King, P.B., 1969. The tectonics of North America: U.S. Geol. nia, Riverside Survey Prof Paper 628, 94 p., map scale 1:5,000,000. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 39

Larsen, E.S., 1948, Batholith and associated rocks of Corona, Popenoe, W.P,. Imlay, R.W., and Murphy, M.A., 1960, Correlation Elsinore, and San Luis Rey quadrangles, southern Califor- of the Cretaceous formations of the Pacific coast (United nia: Geol. Soc. America Mem. 29, 182 p. States and northwestern Mexico): Geol. Soc America Bull., V. 71, p. 1491-1540. Mallory, V.S., 1959, Lower Tertiary biostratigrapfiy of the California coast ranges: American Assoc, Petrol. Geol., Scott, N.H., 1971, Preliminary report on felt area and intensity, 297 p. In The San Fernando, California, earthquake of February 9, 1971: U.S. Geol. Survey Prof. Merriam, R., 1968, Geologic reconnaissance of northwest Paper 733, p. 153-154. Sonora: Stanford University Pub. Geol. Sci., v. 11, p. 287. Sears, J.D., Hunt, C.B , and Hendricks, T.A., 1941, Tran- Milow, E.D., and Ennis, D.B., 1961, Guide to geologic field trip of sgressive and regressive Cretaceous deposits in southern southwestern San Diego County: Geol. Soc. America, Cor- San Juan Basin, New Mexico: U.S. Geol. Survey Prof. Paper dilleran Sec, 57th Ann. Mtg., Guidebook, p. 23-43. 193-F, p. 100-121.

Minch, J.A., 1967, Stratigraphy and structure of the Tijuana- Rosarito Beach area, northwestern Baja California, Shor, G.G., and Roberts, E., 1958. San Miguel, Baja California Norte, earthquakes of February. 1956: a field report: Mexico: Geol. Soc. America Bull., v. 78, p. 1155-1178. Seismological Society of America Bull., v. 48, p. 101-116.

Minch, J. A., 1972, The late Mesozoic-early Tertiary framework of continental sedimentation, northern Peninsular Ranges, Slitter, W.V., 1968, Upper Cretaceous Foraminifera from Baja California, Mexico: Unpublished Ph.D. dissertation. southern California and northwestern Baja California, University of California, Riverside. Mexico: The University of Kansas Pubs.. Art. 7, Ser. no. 49, p. 141. Moore, E.J., 1968, Fossil mollusks of San Diego County: San Diego Soc. Nat. History Occasional Paper 15, 76 p. Steineck, P.L., and Gibson, J.M., 1971, Age and correlation of Moore, G. W., 1972, Offshore extension of the Rose Canyon the Eocene Ulatisian and Narizian stages, California: fault, San Diego, California: U.S. Geol. Survey Prof. Paper Geol. Soc. America Bull., v. 82, p. 477-480. 800-C. p. C113-C116. Strand, R.G., 1961. Geologic map of California— San Diego-El Moore, G.W., and Kennedy, M.P., 1970, Coastal geology of the Centre sheet: California Div. Mines and Geology. California— Baja California border area: American Assoc. Petroleum Geologists Guidebook, Pacific Sections, fall Terzaghi, K., and Peck, R.B., Soil in field trip p. 4-9. 1967, mechanics engineering practice: Wiley and Son, New York, 729 p.

Morton, P.K., 1972, Geologic guidebook to the northern Penin- sularRanges, Orange and Riverside Counties, Califomia: Turner, H.C., Ebert, E.E., and Given, R.R., 1968, The Marine en- Prepared jointly by National Assoc, of Geol. Teachers and vironment offshore from Point Loma. San Diego County: South Coast Geological Soc, for N.A.G.T. far western sec- California Department of Fish and Game. Fish Bull. 140. tion meeting, Chapman College, Orange, California.

Weber, F.H., Jr., 1963, Geology and mineral resources of San Nordstrom, C.W., 1970, Lusardi Formation— a post-batholithic Diego County, Califomia: California Div. Mines and Cretaceous conglomerate north of San Diego, Califomia: Geology County Rept. 3, 309 p. Geol. Soc. America Bull., v. 81, p. 601-605.

Peterson, G.L., 1970, Quaterlnlary deformation of the San Diego Wiegand, J.W., 1970, Evidence of a San Diego Bay-Tijuana area, southwestern Califomia: American Assoc. Petroleum fault: Assoc, of Engineering Geologists Bull., v. 7, p. 107- Geologists Guidebook, Pacific Section, fall field trip, p. 121. 120-126.

Wood, H.E., Chaney, R.W., Clark, J., Colbert. E.H.. Jepsen, G.L.. Peterson, G.L., and Kennedy, M.P., 1974, Lithostratigraphic Reeside, J.B.. Jr., and Stock, C., 1941, Nomenclature and variations in the Poway Group near San Diego, Califomia: correlation of the North American Continental Tertiary: San Diego Soc. Nat. History Transactions, v. 17, p. 251-258. Geol. Soc. America Bull., v. 52, p. 1-48.

Peterson, G.L., and Nordstrom, C.E., 1970, Sub-La Jolla unconformity in the vicinity of San Diego, California: Woodford, A.O., Welday, E.E., and Merriam, R., 1968. Siliceous American Assoc. Petroleum Geologists Bull., v. 54, p. 256- tuff clasts in the upper Paleogene of southern California: 274. 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 phosed volcanic, volcaniclastic, and sedimentary rocks; and mid-Cretaceous In 1965 the California Division of Mines and (2) plutonic rocks of the southern California the Geology, in cooperation with the City of San Diego, batholith, which intrude Santiago began a comprehensive geologic investigation of the Peak Volcanics. greater San Diego metropolitan area. This report deals with the geology of the eastern half of that in- Santiago Peak Volcanics vestigation, A similar report has been written on the The Santiago Peak Volcanics comprise an western half and includes the geology of the Del elongate belt of mildly metamorphosed volcanic, Mar, La Jolla, and Point Loma quadrangles (Ken- volcaniclastic, and sedimentary rocks that crop out nedy, 1975). from the southern edge of the Los Angeles basin The La Mesa, Poway, and SW 1/4 Escondido southward into Mexico (Gray et al., 1971). These quadrangles comprise more than 25 percent of the rocks were mapped in the San Diego area by Hanna

greater San Diego metropolitan area (figure 1 ). This (1926, p. 199-204) as "Black Mountain Volcanics," area is underlain by San Diego's richest sand, but that name was pre-empted, and Larsen (1948) gravel, and crushed stone resources, deemed suggested the substitute--Santiago Peak Volcanics. feasibly extractable in today's market for use in the The volcanic rocks range in composition from Mission Valley, Mira Mesa, Poway, and Escondido basalt to rhyolite but are predominantly dacite and suburbs. These resources and others, including rich andesite. The succession is typified by a wide clay deposits, are being rapidly covered by urban variety of breccia, agglomerate, volcanic development. The clay deposits, which are locally conglomerate, and fine-grained tuff-breccia. Highly expansible, in turn constitute a serious geologic silicified rock (probably tufO and a variety of dark, hazard to development. dense, fine-grained hornfels occur locally. To the The geologic mapping and detailed descriptions west, some local, thin, fossil-bearing marine of the rock units are intended to be used as aids in sedimentary rocks are interbedded with the volcanic planning for land use and future development. The and volcaniclastic rocks. Included with the Santiago stratigraphic relationship between the rock units un- Peak Volcanics are a number of small plutons of derlying the study area and those that underlie the mildly metamorphosed gabbro. These are herein in- area to the west (discussed by Kennedy, 1975) are cluded with the Santiago Peak Volcanics because shown in figure 2. they are metamorphosed and were probably feeders Previous geologic investigations that have been for the volcanic rocks rather than parts of the especially useful in this study include a ground batholith. water investigation by A.J. Ellis (1919), a The Santiago Peak Volcanics are hard and ex- stratigraphic and paleontologic study of the La Jolla tremely resistant to erosion and form topographic quadrangle by M.A. Hanna (1926), two papers on highs. Most of the volcanic rocks are dark greenish geology and paleontology of the San Diego area by gray where fresh but weather grayish red to dark L.G. Hertlein and U.S. Grant IV (1939, 1944), and a reddish brown. The soil developed on the Santiago monograph on the mineral resources of San Diego Peak Volcanics is the color of the weathered rock County by F.H. Weber, Jr. (1963). and supports the growth of dense chaparral. The authors would like to extend special thanks Within a narrow 2-kilometer-long belt, ap-

to D.M. Morton and G.W. Moore of the United proximately I km northwest of Rancho Bernardo in States Geological Survey for their suggestions and the Escondidoquadrangle(plate IB), a succession of contributions pertinent to the results of this study. low-grade metamorphic slate and quartzite crops Acknowledgment is due also to M.O. Woodburne, out. These rocks were considered by Larsen (1948) P.K. Morton, G.B. Cleveland, F.H. Weber, Jr., C.H. to belong to the Bedford Canyon Formation. Within Gray, Jr., M.A. Murphy, J. P. Kern, R.G. Strand, and the northeastern part of the Poway quadrangle, a Y.H. Smitter for their enthusiastic help, interesting similar succession was included by Hanna within discussions, and review of the maps and manuscript. 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 PRE-EOCENE DEPOSITS somewhat from more characteristic Santiago Peak Volcanics, the difference is not deemed enough to correlate them with the Bedford Canyon Formation. Basement Complex Age estimates for the Santiago Peak Volcanics The basement complex consists of two principal have ranged from Late Triassic (Hanna, 1926) to mid-Cretaceous (Milow Ennis, 1961). However rock units: (1) the Upper Jurassic Santiago Peak and

Fife et al. ( 1 to be latest Jurassic Volcanics, a succession of deformed and metamor- 967) showed them (Portlandian) based on fossils from sedimentary in- Geologist. Cahlornia Division ol Mines ana Geology -San Diego State University terbeds.

(45) 46 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

Figure 1. Index map showing the location of the La Mesa. Poway, and SW 1/4 Escondido 7.5-minute quadrangles. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 47

Rosario Group COLUMNAR SECTION OF THE SAN DIEGO CONTINENTAL MARGIN The Rosario Group consists of marine and nonmarine clastic rocks that, oldest to youngest, in- Point Formation Qbp '^''P- ^"^ clude the Lusardi I Formation, the Point Loma For- mation, and the Cabrillo Formation. Only rocks of OIn, LIndovista Formation the Lusardi Formation crop out in the La Mesa- Poway-Escondido area. Tsd, San Diego Formation Lusardi Formation Tp, Pomerado Conglomerate Tmv, Mission Valley Formation The Lusardi Formation, in its type area near Tst, Stadium Conglomerate Rancho Santa Fe, is a very poorly sorted, deeply

Tf, Friars Formation weathered boulder conglomerate (Nordstrom, 1970). few of the Tsc, Scripps Formation The exposures Lusardi Formation To, Ardatti Stiale that occur in the mapped area are in a narrow belt Tt, Torrey Sandstone that extends northeastward from the city of Poway Td, Delmor Formation Tms, Mount Soledad (plate 2B). These deposits fill a former stream chan- Formation nel, but the present topography is reversed, with the Cobrillo Formation Kcss, conglomerate capping a long ridge. (sandstone port) now narrow The Kccg, Cabrillo Formation modern drainage is deeply incised into the granitic (conglomerate port) rocks on either side of the ridge. Kp, Point Loma Formation Kl, Lusardi Formation The Lusardi Formation at this locality consists Jsp, Santiago Peak Volcan of poorly sorted, angular to well-rounded clasts that range in size from granules to boulders; some of the Kg, Granitic rocks of ttie boulders exceed 3 m in diameter. The matrix is a souttiern California batliollth medium- to fine-grained quartz and feldspar-rich sandstone that comprises about 50 percent of the unit. The largest and most abundant clasts include Figure 2. Columnar section of the San Diego continental margin. coarse-grained diorite, quartz diorite, and medium- grained granodiorite. These rock types, together with minor amounts of aplite and vein quartz, con- Plutonic of the Rocks stitute about 60 percent of the clasts in the Lusardi Southern California Batholith Formation. Other clasts include a variety of fine- to Plutonic rocks of the southern California very fine-grained, greenish-gray, and dark-gray batholith in the area are quartz diorite and gabbro. metamorphosed tuff. Some of the most distinctive The quartz diorite is typically coarse grained, light and abundant of these clasts have finely crenulated gray and contains large phenocrysts of plagioclase flow banding on weathered surfaces and are very and potassium feldspar. Hornblende and biotite are fine grained, dark, and structureless on fresh sur- present in small amounts. The gabbro varies con- faces. Less distinctive but abundant clasts are fine- siderably in texture and composition but is mostly grained black hornfels and volcanic rocks. to coarse medium grained and medium to dark gray. Most of the rock types found in the Lusardi chief minerals calcic The are feldspar and pyroxene, Formation-are common to the coarse fraction of the and the accessory minerals include trace amounts of Rosario Group as a whole and are considered to be quartz and biotite. derived largely from local plutonic and metamorphic Potassium-argon dates of a gabbro near San rocks (Peterson, 1971). Marcos and a quartz diorite 10 km southeast of The Lusardi Formation rests unconformably on Escondido are respectively 101 and 105 million granitic rocks of the southern California batholith years (Evernden and Kistler, 1970). A lead-alpha and is in turn overlain by the Eocene Stadium date on zircon from quartz diorite in the Woodson Conglomerate. The character and distribution of the Mountain area, 20 km southeast of Escondido, is deposits suggest that the clasts of the Lusardi For- 105 ± 10 million years (Bushee et aL. 1963). mation originated east of the area mapped and Throughout most of the area, the granitic rocks flowed through a long, narrow, fairly steep-walled are deeply weathered. Spheroidal boulders, formed river channel in the vicinity of Poway. The Lusardi as a result of the weathering, range in size from 0.5 Formation lies buried below the San Diego coastal meter to 10 meters. The batholithic rocks where area from the vicinity of Carlsbad south to the weathered are locally very difficult to distinguish Mexican Border (Kennedy and Moore, 1971). from the overlying Eocene Friars Formation, which is largely composed of debris derived from the weathered plutonic basement rock. Careful EOCENE DEPOSITS examination for relict primary features in the plutonic rocks or sedimentary structures in the overlying rocks is necessary to distinguish the La Jolla Group

weathered basement rock from the sedimentary The La Jolla Group (Eocene) is composed of strata. intertongued marine, lagoonal, and nonmarine silt- 48 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200 stone, sandstone, and conglomerate. These rocks, subsequently designated the Pomerado though partially age equivalent, are from oldest to Conglomerate (Peterson and Kennedy, 1974). youngest the Mount Solcdad Formation, Del Mar The arrangement of the three formations in the Formation, Torrey Sandstone, Ardaih Shale, Scripps Poway Group is schematically illustrated in figure 3. Formation, and Friars Formation (Kennedy and The Mission Valley Formation interlongues with the Moore, 1971). Only the Friars Formation crops out underlying Stadium Conglomerate. Where the in the La Mesa-Poway-Escondido area. Mission Valley Formation pinches out and the Pomerado Conglomerate overlies the Stadium Friars Formation Conglomerate in the eastern part of the area, the two The Friars Formation is a nonmarine and units cannot be distinguished. On the geologic map, lagoonal sandstone named for exposures along the where this situation exists, a dashed contact line in- north side of Mission Valley near Friars Road in the dicates the approximate location of the boundary Jolla La quadrangle (Kennedy and Moore, I 971 ). A between these formations. molluscan fauna collected from the type section includes Nekewis to (Gabb) and Ectinochilus canalifcr supraplicarus (Gabb). These species together are indicative 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 .? °7i\° °l'° o°o° facies, which reaches a maximum thickness of 150 m and consists of sandstone with interbeds of claystone. The sandstone is massive, yellowish gray, Figure 3. Schematic diagram o( lithostratigraphic variations medium grained, poorly indurated, and caliche-rich. in the Poway Group and modern erosion surface. The claystone is dark greenish gray, well indurated, and expansible. Fluviatile cobble conglomerate len- Stadium Conglomerate ses and tongues that thicken markedly to the east are The type section of the Stadium Conglomerate especially characteristic of the exposures along the lies within the SW 1/4 La Mesa quadrangle and is eastern margin of the area. approximately 1 km west of Murphy Canyon Road Throughout the mapped area, the Friars For- along the northern wall of Mission Valley near San mation rests unconformably on the basement com- Diego Stadium (Kennedy and Moore, 1971). At the plex and is overlain by sedimentary deposits of type section it consists of a cobble conglomerate Eocene, Pleistocene, age. and Holocene with a dark yellowish-brown coarse-grained sand- Landslides are common in the clay-rich part of stone matrix. The massive conglomerate contains the formation. The clay is predominantly mont- dispersed lenses of fossiliferous crossbedded sand- morillonite, but kaolinite is also present. Sixteen stone. The fossils include calcareous clay samples were collected and physical charac- nannoplankton, mollusks. and Foraminifera. The teristics were analyzed. The results are presented nannoplankton include Reticulofenestra umbilica on table 1 and are discussed below under Landslide (Levin) and Discoaster distinctus Martini. These Deposits. species when considered with the entire flora collected indicate a middle or late Eocene age (Kennedy, 1973).

The Stadium Conglomerate is moderately well Poway Group sorted with clasts of cobble size predominating. The Poway Conglomerate of Ellis (1919) is one Boulders as large as 0.5 m in diameter do occur but of the most widespread and distinctive rock units in are extremely rare. Fine-grained rocks within the southern California. It crops out primarily in the Stadium Conglomerate generally constitute less than eastern part of the San Diego area and is the 20 percent of the unit, but locally sandstone beds dominant formation in the Poway and La Mesa and lenses may comprise as much as 50 percent of quadrangles (plates 2B,3B). The rock is mostly non- the unit. marine sandstone and coarse cobble conglomerate The highly distinctive "Poway" clasts consist composed largely of clasts that have been described predominantly (up to 80 percent) of mildly in detail by Bellemin and Merriam (1958), DeLisle metamorphosed rhyolitic to dacitic volcanic and et al. (1965), Woodford et al. (1968), and Peterson volcaniclastic rocks and up to 10 percent quartzite. (1970a). This suite of clasts first appears in the Eocene for- In a recent revision of the Eocene stratigraphic mations of the San Diego area and is typical of nomenclature of the San Diego area (Kennedy and stratal units such as the Stadium Conglomerate and Moore, 1971), the Poway Conglomerate was raised Pomerado Conglomerate. The clasts also are abun- to the Poway Group and three formations were dant and characteristic in later stratal units such as recognized within it: a lower conglomerate the Pliocene San Diego Formation, the Pleistocene designated the Stadium Conglomerate, an in- Lindavista Formation, and the various Quaternary termediate sandstone designated the Mission Valley surficial deposits. Formation, and an unnamed upper conglomerate The volcanic and pyroclastic clasts of the formation. This upper conglomerate unit has been Poway suite are distinctively different from the local 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 49

Santiago Peak Volcanics and no local quartzite out- Pomerado Conglomerate crops, which compare to the quartzite clasts in the The Pomerado Conglomerate is the uppermost Eocene conglomerate, are known. The provenance formation of the Poway Group and has a maximum of the "Poway" clasts has provoked considerable thickness of 55 meters. It was named for exposures controversy, and widely differing source areas located at the divide between Carroll Canyon and ranging from the Mojave Desert to Sonora, Mexico, Poway Valley along Pomerado Road (Peterson and have been proposed (DeLisle et al.. 1965; Merriam, Kennedy, 1974). The Pomerado Conglomerate is a 1968; Woodford et al.. 1968; Minch, 1972). The massive cobble conglomerate, lithologically iden- direction of stratigraphic thinning, cobble im- tical to the Stadium Conglomerate. The contact bet- brications, and cross-bedding within the Stadium ween the Mission Valley Formation and Pomerado Conglomerate imply that the clasts were transported Conglomerate is conformable and gradational. East into their present position from an easterly direc- of the pinch-out of the Mission Valley Formation, tion. where the Pomerado Conglomerate rests directly on The Stadium Conglomerate conformably the Stadium Conglomerate, the contact is based on overlies the Friars Formation and is conformably an eastern projection of the feather edge of the overlain by the Mission Valley Formation. Mission Valley Formation along an assumed horizontal surface. Mission Formation Valley Both the Stadium Conglomerate and Pomerado The Mission Valley Formation is composed of Conglomerate are characterized by occasional thin marine, lagoonal, and nonmarine sandstone that lies beds, lenses, and tongues of light brown medium- conformably upon the Stadium Conglomerate and is grained sandstone. Most of these are not large conformably overlain by the Pomerado enough to map. Locally they constitute up to about Conglomerate. The Mission Valley Formation has a 20 percent of the formation. maximum thickness of 60 m and was named for ex- A 10 m thick sandstone lens, designated the posures along the south wall of Mission Valley on Miramar Sandstone Member of the Pomerado the west side of State Highway 163 in the adjacent Conglomerate (Peterson and Kennedy, 1974), crops La Jolla quadrangle (Kennedy and Moore, 1971). out in the vicinity of Miramar Reservoir. The sandstone is characteristically soft and friable, Lithologically, the Miramar Sandstone Member is light olive gray, and fine to medium grained. It is nearly identical to the Mission Valley Formation but locally interstratified with carbonate cemented beds. is stratigraphically higher and wholly contained Cobble conglomerate tongues within the Mission within the Pomerado Conglomerate. Its outcropping Valley Formation, which are identical to the characteristics and topographic expression are also Stadium Conglomerate in lithology, comprise up to very similar to those of the Mission Valley For- 30 percent of sections measured in the easternmost mation. exposures but less than 15 percent of sections The Pomerado Conglomerate and associated measured in the western part of the area. Miramar Sandstone Member have not yielded Due to the friable nature of the Mission Valley fossils; but, on the basis of its stratigraphic Formation, it lacks the bold topographic expression relationship with the underlying fossiliferous of the resistant conglomerate formations that lie Mission Valley Formation (figure 3) , it is assigned stratigraphically above and below. Thin deposits of to the upper Eocene. conglomeratic slope wash commonly mask the Mission Valley Formation in the eastern part of the area, where it is overlain by the Pomerado POST-EOCENE DEPOSITS Conglomerate. The slopes developed in this area are relatively steep on the Pomerado Conglomerate, shallow on the Mission Valley Formation, and steep Pliocene and Pleistocene Rocks on the Stadium Conglomerate. An understanding of The Pliocene and Pleistocene rocks include these topographic relationships helps to determine marine sandstone and conglomerate of the Pliocene the distribution of the Mission Valley Formation in San Diego Formation, marine and nonmarine sand- areas where it is covered by surficial deposits. stone of the late Pliocene or early Pleistocene Lin- The Mission Valley Formation thins from west davista Formation, and lagoonal and nonmarine to east (figure 3), pinching out in the eastern part of sandstone of the late Pleistocene Bay Point For- the Poway and La Mesa quadrangles(plates 2B, 3B). mation. The Bay Point Formation is not present in The rock contains an upper Eocene molluscan the La Mesa-Poway-Escondido quadrangles. fauna. An assemblage collected from the uppermost beds of the Mission Valley Formation in a road cut San Diego Formation 200 m due east of the Miramar Reservoir filtration The San Diego Formation (Dall, 1898), middle plant (elevation 238 m) at Lat 32° 54.8' N.; Long or late Pliocene in age, crops out along the upper

1 17° 05.7' W. includes Tellina tehachapii Anderson part of the north facing slopes of Mission Valley. and Hanna, MacrocaUista Anderson! Dickerson, These exposures, which attain a maximum thickness Crassatella uvasana s.s. Gabb, and Turritella uvasana of 30 m, are typically yellowish-brown, fine- to sargeanti (Anderson and Hanna). These species medium-grained, poorly indurated sandstone. Cob- when considered together are indicative of the upper ble conglomerate beds, bentonite, marl, and brown Eocene age (Tejon Stage) and correlative with the mudstone further characterize the section. The San upper Eocene of Europe (Givens, 1974). Diego Formation increases to the south, where it 50 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

has a maximum thickness of about 400 m (Hertlein St re a nn -Terrace Deposits

and Grant, 1939). The lower 200 m of this section Stream-terrace deposits have been preserved in correlates with the Miocene-Pliocene Rosarito only a few places in the mapped area. These include Beach Formation in northern Baja California. The a poorly consolidated, conglomeratic sand deposit cobble-conglomerate stringers are composed near the confluence of Sycamore Canyon and the San primarily of "Poway-type" clasts ; but, in some beds, Diego River channel, approximately 2 km west of clasts of granitic and metavolcanic rocks, derived Santee, and a coarse-grained sand deposit at the from the local basement, comprise up to 50 percent mouth of Mission Gorge near Mission Valley. Also of the total. The bentonite is light brown, waxy to unmapped conglomeratic stream-terrace deposits earthy, expansible, and soft. are found in several road cuts excavated for the old The San Diego Formation rests unconformably Mission Gorge highway, approximately 0.5 km nor- on rocks of the Poway Group and is overlain by the theast of the gaging station shown on plate 3B.

Lindavista Formation, Locally it is separated from the Lindavista Formation by an unconformity, but Landslide Deposits elsewhere the bedding of the two units is parallel and appears gradational. The area is underlain in large part by incompetent sedimentary rocks which have been Lindavista Formation broadly dissected by shallow weslward-tTowing streams. Most of the landslides in the map area are The Lindavista Formation was named by Hanna rotational slumps and have occurred along valley (1926) for exposures at the Lindavista railroad walls where rocks of the Friars and Mission Valley siding 4 km west of the mapped area within the La Formations occur. The sliding, commonly Jolla 7.5 minute quadrangle. The formation consists associated with soft, expansible clay beds within of nearshore marine, beach, and nonmarine these units, is the result of the combined factors of sediments deposited on a 10 km wide wave-cut plat- incompetent rock, ground water, steep slope angle, form (Lindavista Terrace of Hanna, 1926) during a and basal undercutting of slopes by streams. period of time that post-dates the San Diego For- mation of middle or late Pliocene age and pre-dates Most of the stream channels that dissect the the fossiliferous late Pleistocene (Sangamon Stage) soft sedimentary cover are strongly asymmetrical Bay Point Formation. A fossil molluscan fauna with their steep side exposed to the north. These

found in the Lindavista Formation near Lat. 32° slopes are commonly I to 15 degrees steeper than

48.5' N.; Long. 1 17° 6.25' W., includes the extinct those facing south which seldom reach angles species Pecten bellus. Because this species is not greater than 30 degrees. The over-steepening is con- known from the late Pleistocene, the Lindavista For- trolled in part by the presence of resistant im- mation at this locality is considered to be early permeable rock layers (Pomerado and Stadium Pleistocene in age (G. Kennedy, 1973). Conglomerate) exposed along the upper slopes as erosional ledges and platforms. ledges protect The Lindavista Formation in the mapped area is The reddish-brown sandstone and conglomerate. the softer incompetent material directly beneath Ferruginous cement, mainly hematite, gives the Lin- them (Friars and Mission Valley Formations) from erosion. Westward-thinning davista Formation its characteristic color and a conglomerate tongues resistant, ledgy nature. of the Pomerado and Stadium Conglomerates crop out along the upper valley slopes over a large part of Both the coarse and fine-grained rocks of the the area that lies between Rancho Bernardo and Lindavista Formation have been largely derived Fortuna Mountain(plates 2B, 3B). Landslides occur from Eocene formations of the area, particularly the beneath these beds in the soft sandstone and Poway Group. Iron-staining is common to the Lin- claystone of the Friars and Mission Valley For- davista Formation, and, where it extends downward mations. into the underlying Eocene rocks, the two become difficult to differentiate. A particularly difficult area Several man-induced slides in the Rancho Ber- for separating the Lindavista Formation from ex- nardo area were studied, and all were found to occur tensively stained Stadium Conglomerate lies east beneath resistant conglomerate layers within the and southeast of Miramar Naval Air Station in the soft sandstone and claystone. Stability filling (com- vicinity of Camp Elliott. The upper surface of the pacted fill placed over a benched cut slope) may be this Lindavista Formation is commonly characterized by one means by which type of failure can be "mima mounds" or "Prairie Mounds," small mound- avoided. Because landslide incidence is greatly increased during periods of high rainfall, as a result of like hills up to about 10 m in diameter and 1 m high which are useful in differentiating this unit from the lowered internal rock strength, subdrainage may be rocks of the Poway Group. another means of slope control. Slopes steeper than 30 degrees underlain by clay-rich facies of the Friars Formation in the Ran- Pleistocene and Holocene cho Bernardo, Poway Valley, and Mission Gorge Surficial Deposits areas are mantled with surficial landslide debris that coalesces with slope wash and alluvium in the The Pleistocene and Holocene surficial valley bottoms. Sixteen samples of claystone were deposits include stream-terrace, landslide, collected from these areas (plates 1 B-3B) and analyz- alluvium, and slope wash deposits. ed for their physical properties. 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 51

The results of Atterberg tests and the quantity pansive clay horizons weathered from bedrock sour- of individual size fractions from particle size ces and deposited as slope wash yield the hum- distribution tests of these samples are shown in mocky topography that is common to much of this table 1. area.

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 STRUCTURE 0.074 to 2.0 millimeters. The liquid limit (LL) is defined as the minimum moisture content at which AND SEISMIC HISTORY the material behaves as liquid using this test. The The oldest rocks in the study area, the upper plastic limit (LP) is defined as the minimum Jurassic Santiago Peak Volcanics are massive, com- moisture content at which the sample behaves plexly deformed, and their structure within the mapped plastically using this specified test procedure. The area is not readily decipherable. They have undergone plasticity index (IP) is the numerical difference bet- low-grade metamorphism and have been intruded by ween the liquid limit and the plastic limit. The rocks of the mid-Cretaceous southern California plasticity index is then the range of moisture content batholith. over which the sample behaves plastically. There Regional uplift followed deformation, exists a direct relationship between the liquid limit metamorphism, and batholithic intrusion near the close and "compression index," and between the liquid of the Mesozoic Era, and deep-seated batholithic rocks limit and the "coefficient of consolidation," whereas were extensively exposed. An erosion surface having in an inverse relationship exists between the plasticity excess of 500 m relief was developed on these rocks, index and "shearing resistance" (lerzaghi and Peck, setting the stage for deposition of sedimentary rocks in 1967). the Late Cretaceous and Tertiary periods (Peterson and Nordstrom, 1970). The stated median particle size was taken from the 50 percent cumulative level of particle size The basement rocks have acted as a rigid platform distribution graphs. The arithmetic mean of the from Late Cretaceous time to the present and the post- batholithic sedimentary rocks deposited upon them are median particle sizes among all the samples is 0.016 only slightly deformed and mostly flat-laying (section mm (16 microns), which is in the lower portion of A-A', units the silt range. B-B'). Mapping of the rock over a broad area has demonstrated that inclinations locally associ- Associations between plasticity index, particle ated with Tertiary and Quaternary faulting are rarely size, and the percentage of clay-size particles are greater than 2 degrees. readily observed from the data of table 1. The Evidence for Late Cenozoic uplift and faulting medium-plasticity samples (IP=il0 to 20) have an within the mapped area is abundant (Moore and Ken- average median particle size of 47 microns. High- nedy, 1970; Peterson, 1970b; Moore, 1972; Ziony and plasticity samples (IP = 20 to 40) have an average Buchanan, 1972). Uplift of the Lindavista terrace is median particle size of 14 microns. The very-high- evident in that the early Pleistocene shoreline associ- plasticity samples (IP > 40) have a mean particle ated with the present landward extension of the Lin- size of 6 microns. A direct relationship between davista Formation lies at an altitude of nearly 1 65 m in higher plasticity and landslide incidence can be seen the western part of the Poway and La Mesa quad- by comparing this data with field observations in rangles. that both the surficial and bedrock landslides in the areas sampled are more abundant with an increase The Poway terrace, which is extensively developed in the eastern part of the Poway and quad- in the plasticity index. Nearly all of the landslides La Mesa rangles, lies at an altitude of about 275 to 325 meters. mapped have occurred in rocks with a plasticity index greater than 20. 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 Alluvium Slope and Wash a stripped structural surface developed on the resistant Alluvium in the area consists primarily of upper surface of the Pomerado Conglomerate. consolidated poorly stream deposits of silt, sand, Pleistocene or younger faults in the study area oc- and cobble-sized particles derived from bedrock cur in the vicinity of Collwood Boulevard and Mon- sources that lie within and to the east of the study tezuma Road, Murphy Canyon, and Mission Gorge. A area. alluvium is The intertongued with Holocene post-Lindavista fault is inferred to coincide with at slope wash that generally mantles the lower valley least the southern part of Murphy Canyon and the slopes throughout the area. For this reason, southern part of Mission Gorge because the Lindavista alluvium and slope wash have not been dif- Formation lies topographically higher on the west side ferentiated in most areas. of these canyons. The slope wash deposits consist primarily of Holocene seismic activity along several faults that poorly consolidated surficial materials derived from lie within 10 km of the area is supported by (1) the nearby soil and decomposed bedrock sources. This historic seismicity believed to be associated with the reworked debris is deposited along the flanks of the Rose Canyon fault zone in the San Diego Bay area and lower valley slopes by the action of gravity and sur- (2) subbottom acoustic profiles showing Holocene sedi- face water. Thick deposits of slope wash are com- ments offset on the sea floor at a location 25 km north monly associated with thick soil horizons developed of La Jolla within the Rose Canyon fault zone (Moore, on the Friars and Mission Valley Formations. Ex- 1972). 52 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 53 54 CALIFORNIA DIVISION OF MINES AND GEOLOGY BULL. 200

clay, and lightweight aggregate. Table 1 summarizes (1963). The mines, pits, and quarries in the area are the physical properties of 16 clay samples collected listed in table 2. Mineral-resource inventories are from the Friars Formation. made annually by the Natural Resources Division, The mineral resources and mineral industry of San Diego County Department of Agriculture, and San Diego County are discussed in detail by Weber 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* 1975 GEOLOGY OF THE SAN DIEGO METROPOLITAN AREA, CALIFORNIA 55

Table 2. Mines, THIS BOOK IS DUE ON THE LAST DATE STAMPED P'V ' S6 CALIFO!.. . . >Li -J." ' >GY BULL. 200

REFERENCES CITED

Bellemin. G.J.. and Merriam, R., 1958. Petrology and origin of Kem, J. P.. 1971, Paleoenvironmental analysis of a late the Poway conglomerate, San Diego County. California; Pleistocene estuary in southern California: Journal of Geol. Soc. America Bull., v. 69. p. 199-220. Paleo., V. 45, p. 810-823.

Bukry, David, and Kennedy, MP., 1969. Cretaceous and Eocene Larsen, E.S., 1948, Bathollth and associated rocks of Corona, coccoliths at San Diego. California, in Stiort contributions to Elsinore. and San Luis Rey quadrangles, southern Califor- California geology: California Division of f^ines and Geology nia: Geol. Soc. America Mem. 29. 182 p Special Report lOO. p. 33-43. Merriam, R., 1968, Geologic reconnaissance of northwest Bushee. J., Holden, J., Geyer, B., and Gastil, G., 1963. Lead- Sonora: Stanford University Pubs. Geol. Sci., v. 11, p. 287. alpfia dates for some basement rocks of southwestern California Geol. Soc. America Bull., v. 803-806. 74, p. Milow, E.D., and Ennis, D.B.. 1961. Guide to geologic field trip of southwestern San Diego County: Geol. Soc. America Cor- Dall, W.H., 1898, 18th Ann. Rept.; U.S. Geol. Survey, pt. 2, dilleran Sec. 57th Ann. Mtg., Guideljook, p. 23-43. correlation table opp. p. 334.

Minoh, J. A., 1972, The late Mesozoic early Tertiary framework DeLisle, M.. Morgan, J.R., Heldenbrand. J., and Gastil. G., 1965, — cf continental sedimentation, Lead-alpha ages and possible sources of metavolcanic northem peninsular ranges, Baja California, Mexico: Unpublished Ph.D. Dissertation, rock clasts in the Poway conglomerate, southwest Califor- University of California, Riverside. nia: Geol. Soc. America Bull., v. 76, p. 1069-1074.

Ellis, A.J., 1919, Geology, western part of San Diego county, Moore, G.W., 1972, Offshore extension of the Rose Canyon California: U.S. Geol. Survey Water-Supply Paper 446. p. 50- fault, San Diego, California: U.S. Geol. Survey Prof. Paper 76. 800-C.

Evernden, J.F., and Kistler, R.W., 1970, Chronology of em- Moore, G.W., and Kennedy, M.P., 1970, Coastal geology of the placement of Mesozoic batholithic complexes in California California-Baja California border area: American Assoc. and western Nevada: U.S. Geol. Survey Prof. Paper 623, 42 Petroleum Geologists Guidebook, Pacific Section tall field P trip, p. 4-9.

Fife, D.L., Minch, J. A., and Crampton, P.J., 1967, Late Jurassic Nordstrom, C.E., 1970. Lusardi Formation a post-toatholithic Age of the Santiago PeaV Volcanics. California: Geol. Soc. — Cretaceous conglomerate north of San Diego. California: America Bull., v. 78, p. 299-304. Geol. Soc. America Bull., v. 81. p. 601-605

Givens. C.R., 1974, Eocene molluscan biostratigraphy of the Pine Mountain area, Ventura County, California: University Peterson, G.L.. 1970a, Distinctions between Cretaceous and Eocene in the of California, Dept. of Geol. Sci. Bull., v. 109, 107 p. conglomerates San Diego area, southwestern California: American Assoc. Petroleum Geologists

Gray, C.H., Jr.. Kennedy, MP., and Morton. P.K.. 1971. Petroleum Guidebook. Pacific Section fall field trip. p. 90-98. potential of southern coastal and mountain area. Califor- nia: American Assoc. Petroleum Geologists, Mem. 15. p. Peterson. G.L., 1970b. Quaternary deformation of the San Diego 372-383. area, southwestern California: American Assoc. Petroleum Geologists Guidetx)ok, Pacific Section fall field trip. p. 120- Hanna, M.A., 1926, Geology of the La Jolla quadrangle. Califor- 126. nia: University of California. Dept. Geol. Sci. Bull., v. 16, p. 187-246. Peterson. G.L, 1971. Stratigraphy of the Poway area, southwestern Califorpip- San Diego Soc. Nat. History Tran- Henlein, L.G., and Grant. U.S., IV., 1939, Geology and oil sactions, V. 16, no. possibilities of southwestern San Diego County: California

Journal Mines and Geol., v. 35. p. 57-78, Peterson, G.L., and Kennedy. MP.. 1974, Lithostratigraphic variations in the Poway Group near San Diego, California: Heniein, L.G.. and Grant, U.S., IV, 1944, The geology and San Diego Soc. of Nat. History Transactions, v. 17, p. 251- paleontology of the marine Pliocene of San Diego. Califor- 258. nia, pt. 1. Geology: San Diego Soc. Nat. History Mem., v. 2, p. 1-72. Shor, G.G., Jr., and Roberts, E., 1958. San Miguel, Baja Califor- Kennedy, G L.. 1973. Early Pleistocene invertebrate faunule nia Norte, earthquakes of February, 1956; a field report; from the Lindavista Formation, San Diego. California: San Seismological Society of America Bull., v. 48, p. 101-116. Diego Soc. of Nat History. Transactions, v. 17, p. 119-128. Terzaghi, K., and Peck, R.B., 1967, Soil mechanics In Kennedy, MP.. 1973. Stratigraphy of the San Diego embayment. engineering practice: John Wiley and Son, New York, 729 p. California: Unpublished Ph D. dissertation. University of

California, Riverside. Weber, F.H . Jr , 1963, Geology and mineral resources of San Diego County. California: California Div. Mines and Kennedy, M.P., 1975, Geology of the Del Mar. La Jolla and Point Geology County Rept. 3, 309 p. Loma quadrangles. San Diego metropolitan area, San Diego County, California: California Div. Mines and Woodford. A.O., Welday. E.E.. and Merriam, R.. 1968. Siliceous Geology Bull. 200A. tuff clasts in the upper Paleocene of southern California;

Geol. Soc. America Bull . v. 79, p. 1461-1486. Kennedy, M.P., and Moore. G W.. 1971. Stratigraphic relations of

upper Cretaceous and Eocene Formations. San Diego Ziony. J. I., and Buchanan. J.M.. 1972, Preliminary report on coastal area, California: American Assoc. Petroleum recency of faulting in the greater San Diego area, Califor- Geologists Bull., v. 55, p. 709-722. nia; U.S. Geol. Survey Open-File Rept., 16 p. ir THIS BOOK IS DUE ON THE LAST DATE

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— fj.'-?- i-ltCtS STATE OF CALIFORNIA PREPARED IN THE RESOURCES AGENCY DEPARTMENT OF CONSERVATION THE CITY 2H PREPARED IN COOPERATION C3 WITH THE CITY OF SAN DIEGO GEOLOGY OF THE DEL MAR QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA

by Michael P. Kennedy

SCALE 1 24000

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

EXPLANATION

[q7]

ArtiBcial fill 8 >o

i ^ c g en ^

Landslide deposits

Stream-terrace deposita

Bay Point Formation I

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

Lusardi Formation EH

Santiago Peak Volcanics :ontrol by USGS and USC & GS

2.000' -

i.ooo* - SYMBOLS

Contact

{dashed where approximatety located: dotted where cQnce

Fault, showing dip

{dathed whtre appToximatelu located; dotted where ameeaird: V. upthrown aide; D. dotDnihrown tide; jr-jr^^ ihear toru).

Anticline, showing direction of plunge. H Syncline, showing direction of plunge. X- Strike and dip of bedding. a Landslide with direction of movement indicated by arrows.

Clay sample locality.

Fossil mollusk locality.

Fossil coccolith locality.

Fossil vertebrate locality.

LOCATION MAP

TORREY PINES FAULT

SALK FAULT

11 If 11 STATE OF CALIFORNIA PREPARED IN COOPE CALIFORNIA DIVISION OF MINES AND GEOLOGY THE RESOURCES AGENCY WITH OF CONSERVATION JAMES E SLOSSON. STATE GEOLOGIST DEPARTMENT THE CITY OF SAN [ PREPARED m COOPERATION WITH SAN D EGO METROPOLITAN AREA THE CITY OF SAN DIEGO BULLETIN 200 PLATE 3A 30 GEOLOGY OF THE POINT LOMA QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA

by Miohapl P. Kennedy

SCALE 1 24000

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

1975

EXPLANATION

Beach aand

Alluvium

Landslide deposits

I Qbp

I Bay Point Formation

Lin davista 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 »y. «3

-H-"

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

\- 1970 . 20027 GEOLOGY CHAEL P KENNEDY.

ROSE CANYON FAULT ZONE ISM

Ecoan« roeki undlfTsra STATE OF CALIFORNIA PREPARED IN COOPERATION THE RESOURCES AGENCY WITH DEPARTMENT OF CONSERVATION THE CITY OF SAN DIEGO '9Si2'30" PREPARED IN COOPERATION DIEGO METROPOLITAN WITH SAN AREA a , THE CITY OF SAN DIEGO BULLETIN 200, PLATE 3B 117*00"

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

ConliolbyUSGSanc Fault, showing dip

{dashed where approzimaleii/ located; ' " dolled' where' ere eonceaied:eonceaie<' U." uplhrovm

: D. downlh

Landslide with direction of movement indicated by arrows.

Clay sample locality.

Pit, quarry, or mine.

Fossil coccolith locality.

Fossil vertebrate locality.

^^.. STATE OF CALIFORNIA PREPARED IN COOPERATION THE RESOURCES AGENCY WITH DEPARTMENT OF CONSERVATION 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 8 EXPLANATION I

c - '2 Alluvium and Slopewash 5 5> T 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

'oximatelu located: STATE OF CALIFORNIA PREPARED IN COOPERATION CALIFORNIA DIVISION OF MINES AND GEOLOGY THE RESOURCES AGENCY WITH JAMES E. SLOSSON, STATE GEOLOGIST DEPARTMENT OF CONSERVATION THE CITY OF SAN DIEGO 2H PREPARED IN COOPERATION METROPOLITAN AREA WITH SAN DIEGO (^3 BULLETIN 200, PLATE IB THE CITY OF SAN DIEGO 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

CONTOUR INTERVAL 20 FEET DOTTED LINES REPRESENT 10 FOOT CONTOURS DATUM IS MEAN SEA LEVEL

1975

EXPLANATION

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: 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

I L^

GEOLOGY MAPPED BY MICHAEL P KENNEDY. 1971 ^