The Ventura Basin comprises a much-folded and faulted geosynclinal area extending nearly east-west between the Santa Ynez-Topa Topa Mountains on the north, and the Channel Islands-Santa Monica Mountains uplift on the south. A long period of predominantly marine sedimentation from Cretaceous to Pleistocene time was interrupted by an important episode of non-marine deposition in the Oligocene, and by extensive volcanic extrusions in the Miocene. The rocks assumed essentially their present attitudes as a result of several periods of deformation, culminating in late Pleistocene time.

Nearly all of the anticlines and possible fault-trap areas in that part of the basin now above sea-level have been tested to some degree by drilling, and many oil fields have been discovered. Other oil accumulations may be found by deeper drilling in some of the fields, and further exploration may discover additional fault-trap and stratigraphic-trap accumulations. Within the past 5 years, considerable exploratory effort has been expended in the submerged parts of the basin, and it appears possible that offshore discoveries will result from eventual drilling in these parts of the basin.

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