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The Great Central Valley is an alluvial plain, about 50 miles wide and 400 miles long, between the Coast Ranges and Sierra Nevada. The valley is mostly drained by the Sacramento and San Joaquin rivers, which join in the Delta and flow into San Francisco Bay. The eastern border is the west-sloping Sierran bedrock surface, which continues westward beneath alluvium and older sediments. The western border is underlain by east-dipping Cretaceous and Cenozoic strata that form a deeply buried synclinal trough, lying beneath the Central Valley along its western side. The southern part of the valley is the San Joaquin Valley. Its great oil fields follow anticlinal uplifts that mark the southwestern border of San Joaquin Valley and its southern basin. South of the present location of Fresno, the Kings, Tule, and Kern rivers empty their waters into a slightly lower section of the valley that frequently trapped the flows and created a series of vast, shallow lakes. Only limited vestiges of these are visible today in the Tulare Lake Bed and the Buena Vista Lake Bed. Most of the marshlands were reclaimed here and in the Delta during the early years of the 20th Century.

To the north, the Sacramento Valley plain is interrupted by the Marysville Buttes, an isolated Pliocene volcanic plug about 2,000 feet high. Much of the central, lower portions of the valley remain marshy and at least seasonally flooded today. The principal cities of Sacramento and Marysville and many rural areas rely on a complex of immense dikes to hold back season floods.



Collections of unique aerial panoramas of this region may be seen in the Sacramento Valley, Delta, and San Joaquin Valley sections of the California Atlas of Panoramic Aerial Images.