Seaward from the tideline of the California coast to the base of the continental slope is an area of 100,000 sq km (38,600 sq mi) containing 16 sedimentary basins covering 60,000 sq km (23,200 sq mi) with a volume of 166,000 cu km (39,800 sq mi).

The shelf is less than 10% explored and the activity has been confined largely to the coastal fringe of the Santa Barbara Channel and near Los Angeles. Nevertheless 1.8 billion bbl of oil and 1,200 billion cu ft of gas have been produced from 4,400 exploration and development wells. Reserves are estimated at 4.5 billion bbl.

The region has three distinct tectonic provinces. Clastic sediments with occasional pyroclastic and extrusive igneous rocks are common to all and cherts are abundant in the Santa Maria basin of the northern province. There are no carbonate rocks.

The southern province of 46,600 sq km (18,000 sq mi) is a region of tectonic extension with northwesterly trending horst and graben development that clearly reflects the bathymetry. Nine sedimentary basins occupy the deep-water areas; islands and shallow banks are underlain by thin or older sediments and basement rocks. Maximum sedimentary thickness is probably about 4,000 m (13,100 ft) with a volume of about 56,700 cu km (13,600 cu mi).

The Santa Barbara Channel province trends eastwest. Compressional forces have formed several lines of sharp folds along the northern edge of the basin. Many large faults on the north and south borders show left-lateral movement. Rocks from Cretaceous to Pleistocene aggregate up to 20,000 m (65,600 ft) in thickness. Basement is estimated at 12,000 m (39,360 ft) at the eastern end rising toward the sea floor at the western end. The basin has an area of 5,200 sq km (2,000 sq mi) and a volume of 41,700 cu km (10,000 cu mi).

The northern province has 6 basins covering 31,000 sq km (12,000 sq mi) with a volume of 67,600 cu km (16,200 cu mi). Structural trends are northwest and compression forces are indicated by marginal thrust faulting and folding. Erosional remnants of Upper Cretaceous and lower Cenozoic rocks are common but prospective sediments are of Miocene and Pliocene age. Five of the basins are 3,000 m (10,000 ft) deep or less. The Eel River basin may be as deep as 4,500 m (14,750 ft).

Future potential reserves are estimated as 23.3 billion bbl of oil and 16,200 billion cu ft of gas.

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