The Gulf of California is a long, narrow basin which is almost completely separated from the Pacific Ocean by the mountainous Peninsula of Baja California and bordered on the east by a coastal plain and the Sierra Madre Occidental of Mexico. The northern Gulf, with the exception of the deep Sal si Puedes Basin, is at shelf depth and receives sediment mainly from the Colorado River. Modern deposition is restricted to the vicinity of the Colorado River delta, to areas of sandy littoral sediments fringing the margins, and to somewhat diatomaceous clays in the deepest basin. Over most of the area, glauconitic sands, thought to belong to the post-Pleistocene transgression, occur at the surface.

The central and southern portions of the Gulf consist of a series of basins which increase in depth southward from 500 to nearly 2,000 fathoms. A fairly wide and depositional shelf occurs on the eastern side; the western shelf is narrow, rocky, and mainly erosional. Sediment supply is lateral, and dispersal is essentially perpendicular to the basin axis. The eastern supply is dominant. The distribution and characteristics of the shelf facies are controlled by the rate of sediment supply and the rate of marine redispersal, which are functions of climate and basin shape, respectively. In areas of very low sediment supply, calcarenites occur; elsewhere, the shelf sediments are similar to those of the Gulf of Mexico.

In the deeper portion, several fans occur with thin sand layers, which are presumed to be turbidites. Such fans are found in areas of major sediment supply off the Fuerte and Yaqui Rivers and around Cape San Lucas, where numerous submarine canyons channel turbidity-current flow. Well-defined slope facies can be recognized. The slope facies of the western margin, which is starved with respect to terrigenous material, is fairly calcareous. The deposits of the central basins are diatomites, as a result of the very high organic productivity in surface waters caused by a circulation pattern of wind-driven surface currents which remove surface water to the open Pacific. This surface water is replaced by upwelling of deeper Pacific water rich in nutrients and dissolved silica. All deposited iogenous silica can be accounted for by this mechanism. The southern basins are predominantly terrigenous and very fine grained, notwithstanding the nearness of the sources of sediments.