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The Matilija Sandstone () is a sedimentary geologic unit of Eocene epoch in the Paleogene Period, found in Santa Barbara and Ventura Counties in Southern California. It consists of thick layers of sandstone, made up of grains of feldspar and quartz from a granitic source rock, interbedded with thin layers of siltstone and shale. Hard, massive, and exceptionally resistant to weathering, it forms the high rocky summits of the Santa Ynez Mountain range north of Santa Barbara, eastward into Ventura County.〔Dibblee (1966) 25-26〕 ==Type locality, description, and distribution== The type locality of the unit is at Matilija Hot Springs, along the Ventura River about ten miles (16 km) northwest of Ojai, near to California State Route 33.〔Dibblee (1966) 26〕 At its type locality it is around thick, and consists of both marine and non-marine sandstones with occasional thin beds of micaceous shale separating massive sandstone layers.〔Donald R. Prothero and Justin R. Britt. "Magnetic stratigraphy and tectonic rotation of the Middle Eocene Matilija Sandstone and Cozy Dell Shale, Ventura County, California: implications for sequence stratigraphic correlations." ''Earth and Planetary Science Letters'', Volume 163, Issues 1-4, November 1998, Pages 261-273. 〕 The sandstone layers are made up of well-sorted grains of quartz and feldspar.〔 The unit can be found along the crest of the Santa Ynez range all the way from the western extremity of the mountains near Point Arguello, to its type locality north of Ojai, and east and northeast into the Ventura County backcountry, where Piru and Sespe creeks cross through the formation.〔U.S. Department of Agriculture, Forest Service, Pacific Southwest Region. ''Final Environmental Impact Statement. Land Management Plans for Los Angeles National Forest, Cleveland National Forest, Los Padres National Forest, and San Bernardino National Forest.'' R5-MB-074-B: September 2005. pp. 221, 231, 251. (Available here )〕 It accounts for the highest peaks in the Santa Ynez range, dipping underneath the younger Coldwater Sandstone, Cozy Dell Shale, and Sespe Formation near San Marcos Pass in the center of the range. Thickness of the unit is widely variable, generally decreasing to the west. In its type locality it is around thick; in the vicinity of La Cumbre Peak it is thick; and while it thins to only thick underneath San Marcos Pass, it thickens again to around at the high summits of Santa Ynez and Broadcast Peaks. It thins westward from there, being only thick at Refugio Pass, and less than 300 in the Santa Rosa Hills and west to Point Conception.〔〔Dibblee, Thomas. ''Geology of Southwestern Santa Barbara County, California''. Bulletin 150, California Division of Mines and Geology. San Francisco, 1950. 26-27〕 Along with the younger Coldwater Formation, the Matilija is the source of the enormous sandstone boulders which are found abundantly along the creeks and shoreline of Santa Barbara and Goleta. Additionally, boulders are strewn on hillsides in the upper Riviera, and elsewhere on hillsides and floodplains. These boulders, none of which can be moved even in the most intense modern-day flood events, tumbled down the mountains during Pleistocene-age storms and mudflows of unimaginable intensity. The Matilija Sandstone produces little soil when it weathers, and generally supports only hard chaparral on slopes that are not bare rock. North-facing slopes have some stands of pine and fir in the higher elevations.〔Dibblee (1966) 25〕 The formation appears in boreholes drilled into oil fields offshore, indicating the formation dips steeply underneath the Santa Barbara Channel. At the Point Conception Oil Field, the Matilija is at least thick, and first appears approximately below ground surface.〔California Department of Conservation, Division of Oil, Gas, and Geothermal Resources (DOGGR). ''California Oil and Gas Fields, Volumes I, II and III''. Vol. I (1998), Vol. II (1992), Vol. III (1982). PDF file available on CD from www.consrv.ca.gov. p. 674-675〕 In the Molino Offshore Gas Field, southeast of Gaviota about two miles (3 km) offshore, the formation is at an average of below the sea floor, and a well drilled to had not reached the bottom of the formation.〔DOGGR, p. 667〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Matilija Sandstone」の詳細全文を読む スポンサード リンク
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