Los Angeles Basin
The Los Angeles Basin is the coastal sediment-filled plain located between the Peninsular and Transverse ranges in southern California in the United States containing the central part of the city of Los Angeles as well as its southern and southeastern suburbs (both in Los Angeles and Orange counties). It is approximately 35 miles (56 km) long and 15 miles (24 km) wide, bounded on the north by the Santa Monica Mountains and Puente Hills, and on the east and south by the Santa Ana Mountains and San Joaquin Hills. The Palos Verdes Peninsula, formerly an island, marks the outer edge of the basin along the coast. The confluence of the Los Angeles and Rio Hondo rivers is the center of the basin.[1]'
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[edit] Geology
The sediment in the basin is up to 6 miles (10 km) deep. The basin began to form during the Neogene approximately 15 million years ago (mya), when the terrain was underwater, during a crustal upheaval caused by a clockwise shift in the surrounding mountains. The underlying crustal weakening resulted in the formation of the large bowl of the basin. Sediment from the sea and rivers accumulated in the undersea bowl, building up in thick layers. Approximately 5 million years ago, the crustal stretching subsided and the ocean floor of the basin was forced to the surface. Additional sediment accumulated during the upswell resulting in the floor of the basin as it exists today.
[edit] Petroleum
The accumulation of micro-organisms during this time is believed to be the source of the large deposits of oil, including the large Wilmington Oil Field, that were once under the basin but have been largely extracted.
Other large active oil fields include the Huntington Beach Oil Field, which underlies much of the city of Huntington Beach; and the Torrance Oil Field, adjacent to the Wilmington field on the northwest. Most of the numerous fields in the basin have either been abandoned or greatly scaled back in production since the early part of the 20th century; in the 1890s the oil field directly north of downtown Los Angeles, the Los Angeles City Oil Field, led the state of California in oil production.[2] Some of the oil fields even in the dense urban core remain productive, including the Beverly Hills Oil Field.[3]
[edit] Iodine
In former years iodine was recovered commercially from brine co-produced with oil. Dow Chemical Company operated a number of plants at oil fields in the Los Angeles Basin, and recovered iodine from brines that averaged 50 parts per million iodine. Production started in 1932 and lasted into the 1960s.[4]
[edit] Earthquakes
The sedimentary character of the basin is the principal reason why it is considered especially susceptible to excessive damage during earthquakes. The basin is often compared by geologists[who?] to a "a bowl of jelly" that can shake violently when driven by seismic activity.
[edit] Subsidence
Its loose rock structure has also led to numerous instances of subsidence as a result of petroleum extraction, the most spectacular examples being the Baldwin Hillsmeters.
[edit] See also
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[edit] References
- ^ "The Los Angeles Basin - A Huge Bowl of Sand". LAalmanac.com. http://www.laalmanac.com/geography/ge08e.htm. Retrieved 2010-11-27. "The point where the Los Angeles and Rio Hondo Rivers merge in the City of South Gate is the geologic center for the Los Angeles Basin.'"
- ^ History of Oil Production in California: California Department of Conservation, Department of Oil and Gas
- ^ "Oil and Gas Statistics: 2007 Annual Report" (PDF). California Department of Conservation. December 31, 2007. ftp://ftp.consrv.ca.gov/pub/oil/annual_reports/2007/0102stats_07.pdf. Retrieved August 25, 2009.
- ^ G.I. Smith (1966) "Iodine" in Mineral Resources of California, California Division of Mines and Geology, Bulletin 191, p.198-199.
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