The maximum known marine sections of the Pleistocene are believed to be in southern California. More than 2,500 feet of lower Pleistocene marine and fossiliferous strata are locally present in Ventura Basin at the top of a 19,832+ foot late Cenozoic section which indicates a conformable deposition of marine strata from some time in the Miocene, through the Pliocene, and into the lower Pleistocene.

The principal deformation and locally profound erosion of the petroliferous horizons, and the chief migration of petroleum into commercial pools, occurred, in southern California, in Pleistocene time. These features are hard to reconcile with any supposed short duration of the epoch.

The Pleistocene record in southern California embraces a lower time interval represented by the deposition of 2,500+ feet of marine strata, a middle time interval involving elevation and the local erosion of as much as 5,000 feet of rocks, and an upper time interval embracing subsidence and minor recovery. This record indicates a duration for the epoch in excess of 1,000,000 years.

It is considered that most of Pleistocene time represents a break in the known stratigraphic succession, and that the lack of an adequate sedimentary record and a failure to appreciate the magnitude of erosional intervals has caused the epoch to be generally underestimated.

It is concluded that the terms Pleistocene and Glacial are not synonymous. The Pleistocene is viewed as having had four major divisions: (1) Lower (Pedroian), characterized by a local deposition of marine sediments; (2) Middle (Sierran), involving elevation and erosion; (3) Upper (Glacial), embracing glacial and inter-glacial erosion on portions of the continents; and (4) Uppermost (Champlain subsidence), recording depression.

The indicated Pleistocene duration in excess of 1,000,000 years, and the evidence

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of early diastrophism, is believed to simplify the problem of the enormous accumulations of petroleum in California during the epoch.