William R. Dickinson, Donald R. Lowe; Stratigraphic relations of phosphate- and gypsum-bearing upper Miocene strata, upper Sespe Creek, Ventura County, California. AAPG Bulletin ; 50 (11): 2464–2470. doi:
Economic gypsum and possibly economic phosphate deposits occur in the marine, upper Miocene, Santa Margarita Formation of upper Sespe Creek. The Oligocene-Miocene section preserved in this area is only 4,000 feet thick whereas to the north and in the Ventura basin equivalent strata are 12,500 feet thick. The paleotectonic setting of the area seems to have been that of a platform between two basins. This type of setting occurs elsewhere in the Coast Range Miocene.