On the west side of San Joaquin Valley, California, extending from near Mount Diablo south almost to Coalinga in Fresno County, is an almost continuous outcrop of a body of shale which has very definite characteristics. Lithologically it most resembles certain Tertiary formations in the State and for a long time was referred to the Eocene.1 It was not until 1915 that its age was definitely fixed as Upper Cretaceous by Anderson and Pack and the name “Moreno Shale” given to it.

The type locality of the formation is Moreno Gulch, a small wash extending westward through the Panoche...

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