In July, 1933, while engaged in detailed mapping between Ventura and Santa Paula, California, the writer discovered a condition which should be of general interest to all geologists and paleontologists—namely, a surprising lateral change from southwest to northeast in the fauna of the upper 1000 feet of the Santa Barbara formation. The previous failure to recognize this condition has lead to erroneous mapping and correlation and, consequently, to incorrect structural interpretation. A brief discussion of the stratigraphy of the region will be necessary in order to explain this condition.

The area is located in the Ventura Hills, which lie just north of the Santa Clara Valley of southern California, 10 miles south of the east-west trending Santa Ynez-Topatopa Mountains (Fig. 1). It is about 55 miles northwest of Los Angeles.

In the latter part of Lower Pleistocene time this area was near the center of a narrow geosynclinal . . .

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