Geologic Map of the Santa Barbara Coastal Plain Area, Santa Barbara County, California By Scott A. Minor,1 Karl S. Kellogg,1 Richard G. Stanley,2 Larry D. Gurrola,3 Edward A. Keller,4 and Theodore R. Brandt1 1U.S. Geological Survey, Denver, Colo. 2U.S. Geological Survey, Menlo Park, Calif. 3Consulting Geologist, Santa Barbara, Calif. 4Department of Earth Science, University of California, Santa Barbara, Calif. Pamphlet to accompany Scientific Investigations Map 3001 U.S. Department of the Interior U.S. Geological Survey Geologic Map of the Santa Barbara Coastal Plain Area, Santa Barbara County, California By Scott A. Minor,1 Karl S. Kellogg,1 Richard G. Stanley,2 Larry D. Gurrola,3 Edward A. Keller,4 and Theodore R. Brandt1 1U.S. Geological Survey, Denver, Colo. 2U.S. Geological Survey, Menlo Park, Calif. 3Consulting Geologist, Santa Barbara, Calif. 4Department of Earth Science, University of California, Santa Barbara, Calif. Pamphlet to accompany Scientific Investigations Map 3001 U.S. Geological Survey U.S. Department of the Interior U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2009 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Minor, S.A., Kellogg, K.S., Stanley, R.G., Gurrola, L.D., Keller, E.A., and Brandt, T.R., 2009, Geologic Map of the Santa Barbara Coastal Plain Area, Santa Barbara County, California: U.S. Geological Survey Scientific Investigations Map 3001, scale 1:25,000, 1 sheet, pamphlet, 38 p. iii Contents Introduction.....................................................................................................................................................1 Previous Mapping ..........................................................................................................................................1 Present Mapping............................................................................................................................................2 Geologic Summary.........................................................................................................................................2 Structural Framework ...................................................................................................................................3 Fault Kinematic Constraints .........................................................................................................................6 Timing of Deformation ...................................................................................................................................7 Cenozoic Geologic History ...........................................................................................................................8 Acknowledgments .........................................................................................................................................9 Description of Map Units ............................................................................................................................10 References Cited..........................................................................................................................................35 iv Conversion Factors To convert Multiply by To obtain meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) square kilometer (km2) 0.3861 square mile (mi2) Introduction and others, 2001). [Note: Although Keller and Gurrola (2000) and Gurrola and others (2001) named the structural belt the “Santa Barbara Fold Belt”, we refer to it as a “fold and fault This report presents a newly revised and expanded digital belt” due to the common presence of both surficial folds and geologic map of the Santa Barbara coastal plain area (fig. 1) faults along it.] Strong earthquakes have occurred offshore at a compilation scale of 1:24,000.1 The map depicts the within 10 km of the Santa Barbara coastal plain in 1925 (6.3 distribution of bedrock units and surficial deposits and associ- magnitude), 1941 (5.5 magnitude), and 1978 (5.1 magnitude). ated deformation underlying and adjacent to the coastal plain within the contiguous Dos Pueblos Canyon, Goleta, Santa These, and numerous smaller seismic events located beneath Barbara, and Carpinteria 7.5-minute quadrangles (fig. 2). The and offshore of the coastal plain, likely occurred on reverse- new map supersedes an earlier preliminary geologic map of oblique-slip faults that are similar to, or continuous with, the central part of the coastal plain (Minor and others, 2002; Quaternary reverse faults crossing the coastal plain (Yerkes revised 2006) that provided coastal coverage only within the and Lee, 1987). Thus, faults of the SBFFB pose a significant Goleta and Santa Barbara quadrangles. In addition to new earthquake hazard to the approximately 200,000 people living mapping to the west and east, geologic mapping in parts of within the major coastal population centers of Santa Barbara, the central map area has been significantly revised from the Goleta, and Carpinteria. In addition, numerous Quaternary preliminary map compilation—especially north of down- landslide deposits along the steep southern flank of the town Santa Barbara in the Mission Ridge area—based on Santa Ynez Mountains (Bezore and Wills, 2000) indicate the new structural interpretations supplemented by new bio- potential for continued slope failures and mass movements in stratigraphic data. Several new map units recognized in the developed areas. Folded, faulted, and fractured sedimentary areas of expanded mapping are described. Abundant new rocks in the subsurface of the coastal plain and adjacent Santa biostratigraphic and biochronologic data based on microfossil Barbara Channel are sources and reservoirs for economic deposits identifications are presented in expanded unit descriptions of of oil and gas (Tennyson and Isaacs, 2001), some of which are the marine Neogene Monterey and Sisquoc Formations. Site- currently being extracted offshore. Shallow, localized, sedimentary specific fault kinematic observations embedded in the digital aquifers underlying the coastal plain provide limited amounts of map database are more complete owing to the addition of slip- water for the urban areas, but the quality of some of this ground sense determinations. Finally, the present report includes an water is compromised by coastal salt-water contamination expanded and refined summary of stratigraphic and structural (Upson, 1951; Muir, 1968). The present map compilation pro- observations and interpretations that are based on the compos- vides a set of uniform geologic digital coverages and shape files ite geologic data contained in the new map compilation (see that can be used for analysis and interpretation of these and other Geologic Summary below). The digital geologic database for geologic hazards and resources in the coastal plain region. this map is available on the Internet at: http://pubs.usgs.gov/ sim/3001. The Santa Barbara coastal plain is located in the western Previous Mapping Transverse Ranges physiographic province along an east-west- trending segment of the southern California coastline about The first geologic map produced in the Santa Barbara 100 km northwest of Los Angeles (fig. 1). The coastal plain coastal plain area was a 1:62,500-scale map of the Summer- is defined here as the relatively low elevation (lower than 150 land Oil District by Arnold (1907). Willis (1925) produced to 300 m, depending on location), low- to moderate-relief the first fault map of the entire coastal plain area at a scale of piedmont that generally slopes gently seaward from the steep 1:62,500 as part of an investigation of the large Santa Barbara Santa Ynez Mountains range front on the north to the Santa earthquake of 1925. A second early fault map of the coastal Barbara Channel on the south (figs. 3, 4, and 5). The maxi- plain (providing coverage as far east as Santa Barbara) was mum width of the coastal plain is about 7 km near the cities produced by Hill (1932) at a scale of 1:125,000 in conjunc- of Santa Barbara and Goleta, and narrows to 3 km or less tion with a structural study of faulting in the area. The earliest several kilometers west of Goleta and near Carpinteria (figs. systematic geologic mapping in the study area was by Upson 2 and 6). The coastal plain surface includes several mesas (1951), who mapped the coastal plain region in reconnais- and hills (figs. 3, 4, and 6) that are geomorphic expressions of sance at a scale of 1:31,680 as part of a water-resource study, potentially active folds and partly buried oblique and reverse and by Lian (1954), who mapped the eastern Mission Ridge- faults of the Santa Barbara fold and fault belt that transects the Montecito area at a scale of 1:62,500. Thomas W. Dibblee, Jr., coastal plain (SBFFB, fig. 2) (Keller and Gurrola, 2000; Gurrola (1966) produced the first comprehensive, detailed geologic