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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. It is approximately 35 mi (56 km) long and 15 mi (24 km) wide, bounded by the Santa Monica Mountains, the Verdugo Mountains, and the Santa Ana Mountains. The Palos Verdes Peninsula, formerly an island, marks the outer edge of the basin along the coast. The sediment in the basin is up to 6 mi (10 km) deep. The basin began to form during the Neogene approximately 15 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. The accumulation of micro-organisms during this time is believed to the source of the large deposits of petroleum, including the large Wilmington Oil Field, that were once under the basin but have been largely extracted. Approximately 5 million years ago, the crustal stretching subsided and the ocean floor of the basin was forced to the surface. Additional sedimental accumulated during the upswell resulting in the floor of the basin as it exists today. 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 to a "a bowl of jelly" that can shake violently when driven by seismic activity. External links
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