Scientific Investigations Map 3261
In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology.
The Offshore of Carpinteria map area lies within the central Santa Barbara Channel region of the Southern California Bight. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and the region is presently undergoing north-south shortening.
The small city of Carpinteria is the most significant onshore cultural center in the map area; the smaller town of Summerland lies west of Carpinteria. These communities rest on a relatively flat coastal piedmont that is surrounded on the north, east, and west by hilly relief on the flanks of the Santa Ynez Mountains. El Estero, a salt marsh on the coast west of Carpinteria, is an ecologically important coastal estuary. Southeast of Carpinteria, the coastal zone is narrow strip containing highway and railway transportation corridors and a few small residential clusters. Rincon Point is a well-known world-class surf break, and Rincon Island, constructed for oil and gas production, lies offshore of Punta Gorda. The steep bluffs backing the coastal strip are geologically unstable, and coastal erosion problems are ongoing in the map area; most notably, landslides in 2005 struck the small coastal community of La Conchita, engulfing houses and killing ten people.
The Offshore of Carpinteria map area lies in the central part of the Santa Barbara littoral cell, whose littoral drift is to the east-southeast. Drift rates have been estimated to be about 400,000 tons/yr at Santa Barbara Harbor (about 15 km west of Carpinteria). At the east end of the littoral cell, eastward-moving sediment is trapped by Hueneme and Mugu Canyons and then transported to the deep-water Santa Monica Basin. Sediment supply to the western and central part of the littoral cell is largely from relatively small transverse coastal watersheds, which have an estimated cumulative annual sediment flux of 640,000 tons/yr. The much larger Ventura and Santa Clara Rivers, the mouths of which are about 25 to 30 km southeast of Carpinteria, yield an estimated 3.4 million tons of sediment annually, the coarser sediment load generally moving southeast, down the coast, and the finer sediment load moving both upcoast and offshore.
The offshore part of the map area consists of a relatively flat and shallow continental shelf, which dips so gently (about 0.4° to 0.5°) that water depths at the 3-nautical-mile limit of California’s State Waters are 40 to 45 m. This part of the Santa Barbara Channel is relatively well protected from large Pacific swells from the north and northwest by Point Conception and from the south and southwest by offshore islands and banks. Fair-weather wave base is typically shallower than 20-m water depth, but winter storms are capable of resuspending fine-grained sediments in 30 m of water, and so shelf sediments in the map area probably are remobilized on an annual basis. The shelf is underlain by variable amounts of upper Quaternary shelf, estuarine, and fluvial sediments that thicken to the south.
Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft sediment and isolated areas of rocky habitat that support kelp-forest communities nearshore and rocky-reef communities in deep water. The potential marine benthic habitat types mapped in the Offshore of Carpinteria map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie within the Shelf (continental shelf) megahabitat, dominated by a flat seafloor and substrates formed from deposition of fluvial and marine sediment during sea-level rise. This fairly homogeneous seafloor provides promising habitat for groundfish, crabs, shrimp, and other marine benthic organisms. The only significant interruptions to this homogeneous habitat type are the exposures of hard, irregular, and hummocky sedimentary bedrock and coarse-grained sediment where potential habitats for rockfish and related species exist.
Chapters in the Pamphlet
Chapter 1. Introduction, By Samuel Y. Johnson
Chapter 2. Bathymetry and Backscatter-Intensity Maps of the Offshore of Carpinteria Map Area (Sheets 1, 2, and 3), By Peter Dartnell and Rikk G. Kvitek
Chapter 3. Data Integration and Visualization for the Offshore of Carpinteria Map Area (Sheet 4), By Peter Dartnell
Chapter 4. Seafloor-Character Map of the Offshore of Carpinteria Map Area (Sheet 5), By Eleyne L. Phillips, Mercedes D. Erdey, and Guy R. Cochrane
Chapter 5. Ground-Truth Studies for the Offshore of Carpinteria Map Area (Sheet 6), By Nadine E. Golden and Guy R. Cochrane
Chapter 6. Potential Marine Benthic Habitat Map of the Offshore of Carpinteria Map Area (Sheet 7), By H. Gary Greene and Charles A. Endris
Chapter 7. Subsurface Geology and Structure of the Offshore of Carpinteria Map Area and the Santa Barbara Channel Region (Sheets 8 and 9), By Samuel Y. Johnson, Eleyne L. Phillips, Andrew C. Ritchie, Florence L. Wong, Ray W. Sliter, Amy E. Draut, and Patrick E. Hart
Chapter 8. Geologic and Geomorphic Map of the Offshore of Carpinteria Map Area (Sheet 10), By Samuel Y. Johnson, Andrew C. Ritchie, Gordon G. Seitz, and Carlos I. Gutierrez
Also of Interest
Scientific Investigations Map 3225, California State Waters Map Series—Hueneme Canyon and Vicinity, California, by Samuel Y. Johnson and others.
Scientific Investigations Map 3254, California State Waters Map Series—Offshore of Ventura, California, by Samuel Y. Johnson and others.
Scientific Investigations Map 3281, California State Waters Map Series—Offshore of Santa Barbara, California, by Samuel Y. Johnson and others.
Scientific Investigations Map 3302, California State Waters Map Series—Offshore of Coal Oil Point, California, by Samuel Y. Johnson and others.
Scientific Investigations Map 3319, California State Waters Map Series—Offshore of Refugio Beach, California by Samuel Y. Johnson and others.
First posted August 9, 2013
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Johnson, S.Y., Dartnell, P., Cochrane, G.R., Golden, N.E., Phillips, E.L., Ritchie, A.C., Kvitek, R.G., Greene, H.G., Endris, C.A., Seitz, G.G., Sliter, R.W., Erdey, M.D., Wong, F.L., Gutierrez, C.I., Krigsman, L.M., Draut, A.E., and Hart, P.E. (S.Y. Johnson and S.A. Cochran, eds.), 2013, California State Waters Map Series—Offshore of Carpinteria, California: U.S. Geological Survey Scientific Investigations Map 3261, 42 p., 10 sheets, scale 1:24,000, https://pubs.usgs.gov/sim/3261/.