In this arbitrary division are situated the Cuyama Valley, Carrizo Plain, Salinas Valley, San Andreas trough, Halfmoon Bay-Santa Cruz area, and the Livermore-Contra Costa basin.

Combined area of these basins is 4,500 square miles with an estimated volume of sediments of 6,500 cubic miles. Seventy-five per cent of the sediments are believed to be marine.

Commercial oil production was not discovered until 1948. There are now four substantial producing fields in the Cuyama Valley and two in the Salinas Valley. There were 377 exploratory wells drilled to December 31, 1949.

The complex structure and stratigraphy of these basins make them difficult to prospect and many more wildcats will have to be drilled to explore thoroughly the oil and gas possibilities.

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