The Oxnard field is within the Ventura Basin Province of southern California.
 Geologically, this area is part of a structural downwarp that occurred during the late Pliocene.
 Deposition within the basin occurred fast enough to fill it with up to seven kilometers of sedimentary rock in only five million years.
 While most of the rocks filling the basin are marine sediments, some igneous rocks from the Conejo Volcanics series overlie them.
 Oil accumulations, which are common in the Ventura Basin, mainly occur in anticlinal settings modified by faulting.
 Stratigraphy is also influential in creating traps for hydrocarbons.
 Where the sedimentary rocks are sandstones with high porosity, and the structure and stratigraphy allow hydrocarbons to be trapped on their upward migration, oilfields are found.
 In the Santa Clara Avenue field, oil is trapped in numerous thin layers of oil sands within the Sespe Formation, of Oligocene age.
 Oil is trapped updip where it encounters the impermeable Conejo Volcanics.
 This igneous unit was originally thought to be a canyon fill, but more recently has been interpreted to be a quickly cooling, finely crystalline intrusion.

Because the surface of the Oxnard Plain is flat, giving no hint of the subsurface structure potentially containing oil, the region was overlooked by early drillers.
 In spite of discoveries on all sides -- the Oxnard field to the south, the Ventura field to the northeast, and the South Mountain and Saticoy fields to the northeast -- the field was not found until 1972, by prospectors exploring the edge of the Epworth Syncline.
 Two productive pools were found, both in the Sespe Formation, separated by an igneous intrusion.
The finds were in January 1972 and July 1973.
 Oil is found at great depth -- 9,000 feet in the first pool and 8,600 the other -- and is generally medium-grade, with API gravity of 16 to 28, with a sulfur content of about two percent by weight.
The Oxnard field is within the Ventura Basin Province of southern California.  Geologically, this area is part of a structural downwarp that occurred during the late Pliocene.  Deposition within the basin occurred fast enough to fill it with up to seven kilometers of sedimentary rock in only five million years.  While most of the rocks filling the basin are marine sediments, some igneous rocks from the Conejo Volcanics series overlie them.  Oil accumulations, which are common in the Ventura Basin, mainly occur in anticlinal settings modified by faulting.  Stratigraphy is also influential in creating traps for hydrocarbons.  Where the sedimentary rocks are sandstones with high porosity, and the structure and stratigraphy allow hydrocarbons to be trapped on their upward migration, oilfields are found.  In the Santa Clara Avenue field, oil is trapped in numerous thin layers of oil sands within the Sespe Formation, of Oligocene age.  Oil is trapped updip where it encounters the impermeable Conejo Volcanics.  This igneous unit was originally thought to be a canyon fill, but more recently has been interpreted to be a quickly cooling, finely crystalline intrusion.
Because the surface of the Oxnard Plain is flat, giving no hint of the subsurface structure potentially containing oil, the region was overlooked by early drillers.  In spite of discoveries on all sides -- the Oxnard field to the south, the Ventura field to the northeast, and the South Mountain and Saticoy fields to the northeast -- the field was not found until 1972, by prospectors exploring the edge of the Epworth Syncline.  Two productive pools were found, both in the Sespe Formation, separated by an igneous intrusion. The finds were in January 1972 and July 1973.  Oil is found at great depth -- 9,000 feet in the first pool and 8,600 the other -- and is generally medium-grade, with API gravity of 16 to 28, with a sulfur content of about two percent by weight.
Santa Clara Avenue Oil Field