The post-Miocene sediments of the San Joaquin Valley, California, attaining a total thickness of nearly 14,000 feet, were deposited under varying conditions of marine, brackish, lacustrine, fluviatile, and subaerial sedimentation. Studies covering the southern end of the valley have demonstrated that these sediments may be divided into three main divisions on the basis of lithologic character, fossil content, and diastrophic history indicated. The three divisions comprise cartographic units of formational value.

The writers review the literature dealing with this stratigraphic section and designate the post-Miocene formations in the following manner.

Tulare formation (Pleistocene): lacustrine, fluviatile, and subaerial sediments.

San Joaquin clays (late Pliocene and early Pleistocene): lacustrine, brackish, and marine alternations.

Etchegoin sand (Pliocene): marine sediments.

The middle unit is discussed in detail and further differentiation of the section is shown by a study of the thermal facies.

A tentative correlation of the San Joaquin clay is attempted.

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