Geologic Map of the San Diego 30’ x 60’ Quadrangle, California By Michael P. Kennedy1 and Siang S. Tan1 Digital Preparation by Kelly R. Bovard2, Anne G. Garcia2, Diane Burns2, and Carlos I. Gutierrez1 2008 Prepared in cooperation with: Copyright © 2008 by the California Department of Conservation California Geological Survey. All rights reserved. No part of this publication may be reproduced without written consent of the California Geological Survey. The Department of Conservation makes no warranties as to the suitability of this product for any given purpose. ARNOLD SCHWARZENEGGER, Governor MIKE CHRISMAN, Secretary BRIDGETT LUTHER, Director JOHN G. PARRISH, Ph.D., State Geologist STATE OF CALIFORNIA THE RESOURCES AGENCY DEPARTMENT OF CONSERVATION CALIFORNIA GEOLOGICAL SURVEY __________________________________ 1Department of Conservation, California Geological Survey 2U.S. Geological Survey, Department of Earth Sciences, University of California, Riverside CALIFORNIA GEOLOGICAL SURVEY JOHN G. PARRISH, Ph.D. STATE GEOLOGIST Copyright © 2008 by the California Department of Conservation. All rights reserved. No part of this publication may be reproduced without written consent of the California Geological Survey. The Department of Conservation makes no warranties as to the suitability of this product for any particular purpose. Introduction relatively narrow, westward sloping coastal In 1990 the U.S. Geological Survey, margin that includes the San Diego as part of the National Geologic Mapping embayment. On the east the highlands are Program, initiated the Southern California bounded from the adjoining Colorado Desert Areal Mapping Project (SCAMP) (http:// and the Gulf of California by precipitous fault scamp.wr.usgs.gov) in cooperation with the scarps, 2,000 to more than 3,000 meters high. California Geological Survey (then Division The area within the San Diego 30’ x 60’ of Mines and Geology) Regional Geologic quadrangle is tectonically and seismically Mapping Project (http://www.conservation. active and includes parts of four major, ca.gov/cgs/rghm/rgm/index.htm). SCAMP’s northwest-trending, oblique, right-lateral, objectives were two-fold: to provide a basic strike-slip, Pacific/North American Plate understanding of the geologic framework boundary fault zones. They include the Rose and geologic history of southern California; Canyon-Newport-Inglewood Fault Zone along and to develop a uniform digital geologic the eastern coastal margin of the quadrangle, map database that could be used in a the Palos Verdes-Coronado Bank Fault Zone Geographic Information System (GIS) and offshore on the inner shelf, the San Diego be the foundation for geologic hazard Trough Fault Zone (source of the 1986, investigations, natural resource evaluations, ML=5.3, Oceanside earthquake) in the central and other related earth science studies. offshore region, and the San Clemente Fault These types of digital data can provide an Zone on the outer offshore margin (Fig. 1). important component for performing GIS Within the greater San Diego analyses throughout southern California. metropolitan area, the Rose Canyon Fault This map was prepared by the Zone, as depicted by Kennedy and others Department of Conservation, California (1975), Moore and Kennedy (1975), Kennedy Geological Survey and is a product of and Welday (1980), Clarke and others (1987), SCAMP. This project was supported in part Treiman (1993) and Kennedy and Clarke by the U.S. Geological Survey STATEMAP (2001), includes the Mount Soledad, Old award no. 98HQAG2049. Town, Point Loma, Silver Strand, Coronado and Spanish Bight faults. The Rose Canyon Geologic Summary Fault Zone displaces Holocene sediment in The San Diego 1:100,000-scale Rose Canyon 7 km north of San Diego Bay quadrangle lies within the Peninsular where a late Pleistocene slip rate of 1-2 Ranges Geomorphic Province of southern mm/yr has been estimated (Lindvall and California, between 32°30’ and 33° N. Rockwell, 1995). A study of the recency and latitude and 117° and 118° W. longitude, character of faulting in the greater San Diego and encompasses the greater San Diego metropolitan area suggests a long-term area, the second largest metropolitan area Tertiary slip rate for the Rose Canyon Fault of California (Fig. 1). The Peninsular Zone of about 1-2 mm/yr (Kennedy and Ranges of southern California form a others, 1975). Although there is significant northwest-trending geomorphic province late Quaternary deformation in the San Diego that occupies the southwestern corner of region the seismicity is relatively low (Simons, California and extends southeastward to 1977). form the Baja California peninsula. Its The eastern part of the San Diego physiography is characterized principally by 1:100,000-scale quadrangle is underlain by steep mountain highlands with elevations plutonic rocks of the western Peninsular exceeding 3,500 meters and dramatic Ranges batholith and a thick sequence (>5 intermontane basins, valleys, and rivers. km) of Mesozoic fore-arc and fore-arc basin The highlands are flanked on the west by a volcanic and volcaniclastic deposits. The 1 Figure 1. Index map showing the location of the San Diego 30’ x 60’ quadrangle, major cities and faults, as well as the geomorphic provinces of southwestern California. Modified from Jennings and Saucedo, 2002. batholithic rocks are mostly granodiorite and formed. Marine sedimentary interbeds in tonalite (Fig. 2) and based on U/Pb isotopic Penasquitos Canyon, near Del Mar, contain ages range from 140 Ma to 105 Ma (Silver the fossil Buchia piochii, which indicates a and Chappell, 1988). The andesitic flows Late Jurassic (Tithonian) age for these strata and coarse-grained volcaniclastic breccias of (Fife and others, 1967; Jones and Miller, the Mesozoic fore-arc deposits have, in large 1982). Zircon U/Pb ages from the part, been metamorphosed to low-grade metavolcanic rocks are reported to range greenschist facies and exhibit penetrative from 137 Ma to 119 Ma (Anderson, 1991) deformation. However, in the upper part of indicating that they are coeval with the the section these rocks are not meta- surrounding plutonic rocks of the western morphosed and are only moderately de Peninsular Ranges batholith. Much of the 2 basement rock has been deeply weathered 700 meters thick and grades from non- and altered. The weathered bedrock and marine fan and dune deposits on the east Quaternary alluvial deposits derived from through lagoonal and nearshore beach and them contain expansible clays, mostly beach-bar deposits to marine continental smectite. shelf deposits on the west near the present- The western part of the quadrangle is day coastline. The age and environmental underlain by a relatively thick (>1,000 m) interpretation of the Eocene sequence is succession of Upper Cretaceous, Tertiary based on the mapped distribution of litho- and Quaternary sedimentary rocks that facies coupled with the presence of a pelagic unconformably overlie basement rocks. fossil calcareous nannoplankton flora in the They consist of marine, paralic, and continental shelf facies (e.g., Bukry and continental claystone, siltstone, sandstone Kennedy, 1969), a shallow water molluscan and conglomerate. The Upper Cretaceous fauna in the nearshore facies (e.g., Givens rocks are composed of marine turbidites and and Kennedy, 1979), and a fossil terrestrial continental fan deposits assigned to the vertebrate mammal fauna in the paralic Rosario Group (Kennedy and Moore, 1971). facies (e.g., Golz, 1973). Cross bedding, The Lusardi Formation, the basal formation cobble imbrications, paleostream gradients of the Rosario Group, is a nonmarine and clast petrology indicate a local eastern boulder fanglomerate deposited along the source for these rocks. The nonmarine western margin of a tectonic highland upon a facies of the Eocene formations are typically deeply weathered surface of the older well indurated and cemented whereas the Cretaceous and Jurassic plutonic and lagoonal facies are soft and friable. The metamorphic basement rocks. Clasts within nearshore facies are well indurated, well the Lusardi Formation are composed sorted, and locally concretionary. The exclusively of these weathered basement marine deposits are typically fine-grained, rocks. The Lusardi Formation is overlain by indurated, and cemented. Following the the Point Loma Formation, the middle part of deposition of Eocene rocks, the San Diego the Rosario Group. It is composed mostly of margin was again elevated and eroded. marine sandstone, siltstone and con- During the Oligocene, continental and glomerate sequences that together form shallow water lagoonal deposits of the Otay massive turbidite deposits. The Point Loma Formation were deposited. The Otay Formation is Campanian and Maestrichtian Formation is light-gray and light-brown, in age (Sliter, 1968; Bukry and Kennedy, medium- and coarse-grained, arkosic 1969) and underlies most of the Point Loma sandstone intertongued with light-brown Peninsula and the hills southeast of La Jolla. siltstone and light-gray claystone. Much of It is conformably overlain by the uppermost the claystone is composed of light-gray part of the Rosario Group, marine sandstone bentonite in beds up to 1 m in thickness. and conglomerate of the Maestrichtian Following Oligocene time, the San Diego (Sliter, 1968; Bukry and Kennedy, 1969) coastal margin underwent uplift and Cabrillo Formation. Following the deposition extensive erosion. The next major marine of the Rosario Group, the San Diego coastal transgression did not occur