Nine producing or potentially productive oil fields or areas are located in the Santa Maria district, which lies in the Santa Maria basin in coastal California. Formations in outcrop and subsurface sections range in age from Jurassic(?) to Recent. They have a maximum outcrop thickness of about 13,000 feet. The Monterey shale (middle to upper Miocene) and the Sisquoc formation (upper Miocene (?) to middle Pliocene) are the formations of greatest economic interest, the principal oil zones of the largest fields being in fractured chert and cherty shale of the Monterey. The basin facies of the Sisquoc formation represents a Monterey-like facies of later date than the Monterey proper. The stratigraphic relations of the Sisquoc formation and of overlying Pliocene formations sho a close correlation with structural features and structural history. Deformation took place at the eastern margin of the basin and on anticlines in the basin during late Miocene and Pliocene time. Most of the present anticlines were evidently then growing ridges on the floor of the sea and the present synclines were basins. The principal deformation, affecting the entire region, took place after deposition of the non-marine Paso Robles formation (upper Pliocene to lower Pleistocene (?) ).