Research Article| March 01, 1996 The southern Whidbey Island fault: An active structure in the Puget Lowland, Washington Samuel Y. Johnson; Samuel Y. Johnson 1U.S. Geological Survey, M.S. 966, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Christopher J. Potter; Christopher J. Potter 1U.S. Geological Survey, M.S. 966, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar John J. Miller; John J. Miller 2Mobil Research and Development Corporation, P.O. Box 650232, Dallas, Texas 75265-0232 Search for other works by this author on: GSW Google Scholar John M. Armentrout; John M. Armentrout 3U.S. Geological Survey, M.S. 960, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Carol Finn; Carol Finn 4U.S. Geological Survey, M.S. 964, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Craig S. Weaver Craig S. Weaver 5U.S. Geological Survey at Department of Geophysics, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Author and Article Information Samuel Y. Johnson 1U.S. Geological Survey, M.S. 966, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Christopher J. Potter 1U.S. Geological Survey, M.S. 966, P.O. Box 25046, Federal Center, Denver, Colorado 80225 John J. Miller 2Mobil Research and Development Corporation, P.O. Box 650232, Dallas, Texas 75265-0232 John M. Armentrout 3U.S. Geological Survey, M.S. 960, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Carol Finn 4U.S. Geological Survey, M.S. 964, P.O. Box 25046, Federal Center, Denver, Colorado 80225 Craig S. Weaver 5U.S. Geological Survey at Department of Geophysics, University of Washington, Seattle, Washington 98195 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1996) 108 (3): 334–354. https://doi.org/10.1130/0016-7606(1996)108<0334:TSWIFA>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Samuel Y. Johnson, Christopher J. Potter, John J. Miller, John M. Armentrout, Carol Finn, Craig S. Weaver; The southern Whidbey Island fault: An active structure in the Puget Lowland, Washington. GSA Bulletin 1996;; 108 (3): 334–354. doi: https://doi.org/10.1130/0016-7606(1996)108<0334:TSWIFA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Information from seismic-reflection profiles, outcrops, boreholes, and potential field surveys is used to interpret the structure and history of the southern Whidbey Island fault in the Puget Lowland of western Washington. This northwest-trending fault comprises a broad (as wide as 6–11 km), steep, northeast-dipping zone that includes several splays with inferred strike-slip, reverse, and thrust displacement. Transpressional deformation along the southern Whidbey Island fault is indicated by along-strike variations in structural style and geometry, positive flower structure, local unconformities, out-of-plane displacements, and juxtaposition of correlative sedimentary units with different histories.The southern Whidbey Island fault represents a segment of a boundary between two major crustal blocks. The Cascade block to the northeast is floored by diverse assemblages of pre-Tertiary rocks; the Coast Range block to the southwest is floored by lower Eocene marine basaltic rocks of the Crescent Formation. The fault probably originated during the early Eocene as a dextral strike-slip fault along the eastern side of a continental-margin rift. Bending of the fault and transpressional deformation began during the late middle Eocene and continues to the present. Oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation.Evidence for Quaternary movement on the southern Whidbey Island fault includes (1) offset and disrupted upper Quaternary strata imaged on seismic-reflection profiles; (2) borehole data that suggests as much as 420 m of structural relief on the Tertiary-Quaternary boundary in the fault zone; (3) several meters of displacement along exposed faults in upper Quaternary sediments; (4) late Quaternary folds with limb dips of as much as ≈9°; (5) large-scale liquefaction features in upper Quaternary sediments within the fault zone; and (6) minor historical seismicity. The southern Whidbey Island fault should be considered capable of generating large earthquakes (Ms ≥7) and represents a potential seismic hazard to residents of the Puget Lowland. This content is PDF only. Please click on the PDF icon to access. 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The type Lospe Formation in the Casmalia Hills is an 800-m-thick sequence of sedimentary and minor volcanic rocks. The Lospe is entirely of early Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and {sup 40}Ar/{sup 39}Ar ages of 17.70 {plus minus} 0.03 Ma (mean of seven determinations) and 17.39 {plus minus} 0.12 Ma (mean of six determinations). The {sup 40}Ar/{sup 39}Ar ages were measured on water-laid tuffs; these tuffs may have erupted from the same volcanic source as a welded tuff yielding an {sup 40}Ar/{sup 39}Ar age of 17.79 {plus minus} 0.10 Ma (mean of five determinations) from the Tranquillon volcanics on Tranquillon Mountain in the westernmost Transverse Ranges. Alluvial fan and fan-delta facies within the basal part of the Lospe are as thick as 200 m and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse-grained facies grade upward into a sequence of interbedded sandstone and mudstone that accumulated in a shallow lake. Gypsum layers in the lake deposits contain sulfate depleted in {sup 34}S (0 to +3{per thousand}), suggesting that the sulfur had a hydrothermal origin. The uppermost 30 m of the Lospe consists of storm-deposited sandstone and mudstonemore » containing shallow-marine microfossils. The shallow-marine deposits are abruptly overlain by bathyal marine shale of the Point Sal Formation. The Lospe Formation records active faulting, volcanism, hydrothermal activity, and rapid subsidence during initial formation of the Neogene Santa Maria basin. These events may have resulted from crustal extension related to the beginning of clockwise rotation of the western Transverse Ranges about 18 to 17 Ma.« less
Research Article| November 01, 1990 Comment and Reply on "Discordant paleomagnetic poles from the Canadian Coast Plutonic Complex: Regional tilt rather than large displacement?" Robert B. Miller; Robert B. Miller 1Department of Geology, San Jose State University, San Jose, California 95192-0102 Search for other works by this author on: GSW Google Scholar Samuel Y. Johnson; Samuel Y. Johnson 2U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar James W McDougall; James W McDougall 3U.S Geological Survey, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar R. F. Butler; R. F. Butler 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 Search for other works by this author on: GSW Google Scholar W. R. Dickinson; W. R. Dickinson 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 Search for other works by this author on: GSW Google Scholar G. E. Gehrels; G. E. Gehrels 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 Search for other works by this author on: GSW Google Scholar W. C. McClelland; W. C. McClelland 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 Search for other works by this author on: GSW Google Scholar S. R. May; S. R. May 5Exxon Production Research Co., P.O. Box 2189, Houston, Texas 77252 Search for other works by this author on: GSW Google Scholar D. Klepacki D. Klepacki 5Exxon Production Research Co., P.O. Box 2189, Houston, Texas 77252 Search for other works by this author on: GSW Google Scholar Author and Article Information Robert B. Miller 1Department of Geology, San Jose State University, San Jose, California 95192-0102 Samuel Y. Johnson 2U.S. Geological Survey, Denver, Colorado 80225 James W McDougall 3U.S Geological Survey, Reston, Virginia 22092 R. F. Butler 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 W. R. Dickinson 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 G. E. Gehrels 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 W. C. McClelland 4Department of Geosciences, University of Arizona, Tucson, AZ 85721 S. R. May 5Exxon Production Research Co., P.O. Box 2189, Houston, Texas 77252 D. Klepacki 5Exxon Production Research Co., P.O. Box 2189, Houston, Texas 77252 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1990) 18 (11): 1164–1166. https://doi.org/10.1130/0091-7613(1990)018<1164:CARODP>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Robert B. Miller, Samuel Y. Johnson, James W McDougall, R. F. Butler, W. R. Dickinson, G. E. Gehrels, W. C. McClelland, S. R. May, D. Klepacki; Comment and Reply on "Discordant paleomagnetic poles from the Canadian Coast Plutonic Complex: Regional tilt rather than large displacement?". Geology 1990;; 18 (11): 1164–1166. doi: https://doi.org/10.1130/0091-7613(1990)018<1164:CARODP>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No abstract available First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Research Article| January 01, 1987 Geology of the Holocene surficial uranium deposit of the north fork of Flodelle Creek, northeastern Washington SAMUEL Y. JOHNSON; SAMUEL Y. JOHNSON 1U.S. Geological Survey, M.S. 916, Box 25046, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar JAMES K. OTTON; JAMES K. OTTON 1U.S. Geological Survey, M.S. 916, Box 25046, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar DAVID L. MACKE DAVID L. MACKE 1U.S. Geological Survey, M.S. 916, Box 25046, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1987) 98 (1): 77–85. https://doi.org/10.1130/0016-7606(1987)98<77:GOTHSU>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation SAMUEL Y. JOHNSON, JAMES K. OTTON, DAVID L. MACKE; Geology of the Holocene surficial uranium deposit of the north fork of Flodelle Creek, northeastern Washington. GSA Bulletin 1987;; 98 (1): 77–85. doi: https://doi.org/10.1130/0016-7606(1987)98<77:GOTHSU>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The north fork of Flodelle Creek drainage basin in northeastern Washington contains the first surficial uranium deposit to be mined in the United States. The uranium was leached from granitic bedrock and fixed in organic-rich pond sediments. The distribution of these pond sediments and, therefore, the uranium has been strongly influenced by relict glacial topography, slope processes, and beaver activity.The north fork of Flodelle Creek drainage basin was covered by the Cordilleran ice sheet during the Fraser (late Wisconsin) glaciation. Till and outwash were deposited on the valley slopes and valley floor as ice receded. Outwash incision and melting of stagnant ice led to formation of a terrace and kames. Shortly after deglaciation, a small pond formed in the upper part of the valley when unconsolidated glacial sediment slumped off the valley slopes and restricted drainage. Fluvial processes dominated in the central and downstream parts of the valley for several thousand years after deglaciation, although drainage was partly restricted by kames. Beavers began to occupy and build dams on the wide outwash plains in the valley floor ∼5000 yr B.P. Beaver ponds in the central part of the basin subsequently filled with sediment and were abandoned, whereas downstream ponds remained relatively free of clastic input and are presently occupied by beavers.Ponds in the drainage basin have been sinks for fine-grained, organic-rich sediments. These organic-rich sediments provide a suitable geochemical environment for precipitation and adsorption of uranium leached from granitic bedrock into ground, spring, and surface waters. Processes of pond formation have thus been important in the development of surficial uranium deposits in the north fork of Flodelle Creek drainage basin and may have similar significance in other areas. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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 Coal Oil Point 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 geodetic studies indicate that the region is presently undergoing north-south shortening. Uplift rates (as much as 2.0 mm/yr) that are based on studies of onland marine terraces provide further evidence of significant shortening. The cities of Goleta and Isla Vista, the main population centers in the map area, are in the western part of a contiguous urban area that extends eastward through Santa Barbara to Carpinteria. This urban area is on the south flank of the east-west-trending Santa Ynez Mountains, on coalescing alluvial fans and uplifted marine terraces underlain by folded and faulted Miocene bedrock. In the map area, the relatively low-relief, elevated coastal bajada narrows from about 2.5 km wide in the east to less than 500 m wide in the west. Several beaches line the actively utilized coastal zone, including Isla Vista County Park beach, Coal Oil Point Reserve, and Goleta Beach County Park. The beaches are subject to erosion each winter during storm-wave attack, and then they undergo gradual recovery or accretion during the more gentle wave climate of the late spring, summer, and fall months. The Offshore of Coal Oil Point map area lies in the central part of the Santa Barbara littoral cell, which is characterized by littoral drift to the east-southeast. Longshore drift rates have been reported to range from about 160,000 to 800,000 tons/yr, averaging 400,000 tons/yr. Sediment supply to the western and central parts of the littoral cell, including the map area, is largely from relatively small transverse coastal watersheds. Within the map area, these coastal watersheds include (from east to west) Las Llagas Canyon, Gato Canyon, Las Varas Canyon, Dos Pueblos Canyon, Eagle Canyon, Tecolote Canyon, Winchester Canyon, Ellwood Canyon, Glen Annie Canyon, and San Jose Creek. The Santa Ynez and Santa Maria Rivers, the mouths of which are about 100 to 140 km northwest of the map area, are not significant sediment sources because Point Conception and Point Arguello provide obstacles to downcoast sediment transport and also because much of their sediment load is trapped in dams. The Ventura and Santa Clara Rivers, the mouths of which are about 45 to 55 km southeast of the map area, are much larger sediment sources. Still farther east, eastward-moving sediment in the littoral cell is trapped by Hueneme and Mugu Canyons and then transported to the deep-water Santa Monica Basin. The offshore part of the map area consists of a relatively flat and shallow continental shelf, which dips gently seaward (about 0.8° to 1.0°) so that water depths at the shelf break, roughly coincident with the California’s State Waters limit, are about 90 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. The shelf is underlain by variable amounts of upper Quaternary marine and fluvial sediments deposited as sea level fluctuated in the late Pleistocene. The large (130 km2) Goleta landslide complex lies along the shelf break in the southern part of the map area. This compound slump complex may have been initiated more than 200,000 years ago, but it also includes three recent failures that may have been generated between 8,000 to 10,000 years ago. A local, 5- to 10-m-high tsunami may have been generated from these failure events. The map area has had a long history of hydrocarbon development, which began in 1928 with discovery of the Ellwood oil field. Subsequent discoveries in the offshore include South Ellwood offshore oil field, Coal Oil Point oil field, and Naples oil and gas field. Development of South Ellwood offshore field began in 1966 from platform “Holly,” the last platform to be installed in California’s State Waters. The area also is known for “the world’s most spectacular marine hydrocarbon seeps,” and large tar seeps are exposed on beaches east of the mouth of Goleta Slough. Offshore seeps adjacent to South Ellwood oil field release about 40 tons per day of methane and about 19 tons per day of ethane, propane, butane, and higher hydrocarbons. 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 Coal Oil Point map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats, which lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats, range from soft, unconsolidated sediment to hard sedimentary bedrock. This heterogeneous seafloor provides promising habitat for rockfish, groundfish, crabs, shrimp, and other marine benthic organisms.
First posted March 24, 2016 For additional information, contact: Contact InformationPacific Coastal & Marine Science CenterU.S. Geological SurveyPacific Science Center2885 Mission St.Santa Cruz, CA 95060http://walrus.wr.usgs.gov/ 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 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 subsurface geology.The Offshore of Santa Cruz map area is located in central California, on the Pacific Coast about 98 km south of San Francisco. The city of Santa Cruz (population, about 63,000), the largest incorporated city in the map area and the county seat of Santa Cruz County, lies on uplifted marine terraces between the shoreline and the northwest-trending Santa Cruz Mountains, part of California’s Coast Ranges. All of California’s State Waters in the map area is part of the Monterey Bay National Marine Sanctuary.The map area is cut by an offshore section of the San Gregorio Fault Zone, and it lies about 20 kilometers southwest of the San Andreas Fault Zone. Regional folding and uplift along the coast has been attributed to a westward bend in the San Andreas Fault Zone and to right-lateral movement along the San Gregorio Fault Zone. Most of the coastal zone is characterized by low, rocky cliffs and sparse, small pocket beaches backed by low, terraced hills. Point Santa Cruz, which forms the north edge of Monterey Bay, provides protection for the beaches in the easternmost part of the map area by sheltering them from the predominantly northwesterly waves.The shelf in the map area is underlain by variable amounts (0 to 25 m) of upper Quaternary shelf, estuarine, and fluvial sediments deposited as sea level fluctuated in the late Pleistocene. The inner shelf is characterized by bedrock outcrops that have local thin sediment cover, the result of regional uplift, high wave energy, and limited sediment supply. The midshelf occupies part of an extensive, shore-parallel mud belt. The thickest sediment deposits, inferred to consist mainly of lowstand nearshore deposits, are found in the southeastern and northwestern parts of the map area.Coastal sediment transport in the map area is characterized by northwest-to-southeast littoral transport of sediment that is derived mainly from ephemeral streams in the Santa Cruz Mountains and also from local coastal-bluff erosion. During the last approximately 300 years, as much as 18 million cubic yards (14 million cubic meters) of sand-sized sediment has been eroded from the area between Año Nuevo Island and Point Año Nuevo and transported south; this mass of eroded sand is now enriching beaches in the map area. Sediment transport is within the Santa Cruz littoral cell, which terminates in the submarine Monterey Canyon.Benthic species observed in the Offshore of Santa Cruz map area are natives of the cold-temperate biogeographic zone that is called either the “Oregonian province” or the “northern California ecoregion.” This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, the eastern limb of the North Pacific subtropical gyre that flows from southern British Columbia to Baja California. At its midpoint off central California, the California Current transports subarctic surface (0–500 m deep) waters southward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception (about 300 km south of the map area), although its associated phylogeographic group of marine fauna may extend beyond to the area offshore of Los Angeles in southern California. The ocean off of central California has experienced a warming over the last 50 years that is driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical environment.Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. The kelp beds are the northernmost known habitat for the population of southern sea otters. Common fish species found in the kelp beds and rocky reefs include lingcod and various species of rockfish and greenling.
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 San Gregorio map area is located in northern California, on the Pacific coast of the San Francisco Peninsula about 50 kilometers south of the Golden Gate. The map area lies offshore of the Santa Cruz Mountains, part of the northwest-trending Coast Ranges that run roughly parallel to the San Andreas Fault Zone. The Santa Cruz Mountains lie between the San Andreas Fault Zone and the San Gregorio Fault system. The nearest significant onshore cultural centers in the map area are San Gregorio and Pescadero, both unincorporated communities with populations well under 1,000. Both communities are situated inland of state beaches that share their names. No harbor facilities are within the Offshore of San Gregorio map area. The hilly coastal area is virtually undeveloped grazing land for sheep and cattle. The coastal geomorphology is controlled by late Pleistocene and Holocene slip in the San Gregorio Fault system. A westward bend in the San Andreas Fault Zone, southeast of the map area, coupled with right-lateral movement along the San Gregorio Fault system have caused regional folding and uplift. The coastal area consists of high coastal bluffs and vertical sea cliffs. Coastal promontories in the northern and southern parts of the map area are the result of right-lateral motion on strands of the San Gregorio Fault system. In the south, headlands near Pescadero Point have been uplifted by motion along the west strand of the San Gregorio Fault (also called the Frijoles Fault), which separates rocks of the Pigeon Point Formation south of the fault from rocks of the Purisima Formation north of the fault. The regional uplift in this map area has caused relatively shallow water depths within California's State Waters and, thus, little accommodation space for sediment accumulation. Sediment is observed offshore in the central part of the map area, in the shelter of the headlands north of the east strand of the San Gregorio Fault (also called the Coastways Fault) around Miramontes Point (about 5 km north of the map area) and also on the outer half of the California's State Waters shelf in the south where depths exceed 40 m. Sediment in the outer shelf of California's State Waters is rippled, indicating some mobility. The Offshore of San Gregorio map area lies within the cold-temperate biogeographic zone that is called either the "Oregonian province" or the "northern California ecoregion." This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, an eastern limb of the North Pacific subtropical gyre that flows from Oregon to Baja California. At its midpoint off central California, the California Current transports subarctic surface (0–500 m deep) waters southward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception (about 350 km south of the map area), although its associated phylogeographic group of marine fauna may extend beyond to the area offshore of Los Angeles in southern California. The ocean off of central California has experienced a warming over the last 50 years that is driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical environment. Seafloor habitats in the Offshore of San Gregorio map area, which lies within the Shelf (continental shelf) megahabitat, range from significant rocky outcrops that support kelp-forest communities nearshore to rocky-reef communities in deep water. Biological productivity resulting from coastal upwelling supports diverse populations of sea birds such as Sooty Shearwater, Western Gull, Common Murre, Cassin's Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. The large extent of exposed inner shelf bedrock supports large forests of "bull kelp," which is well adapted for high wave-energy environments. Common fish species found in the kelp beds and rocky reefs include lingcod and various species of rockfish and greenling.
