As a result of field work carried on in 1947 a sequence of foraminiferal samples were collected in 2,300 feet of Lower Tertiary mudstones, siltstones, and interbedded shales and sandstones in the vicinity of Media Agua Creek, in the Temblor Range on the west side of the San Joaquin Valley.

Foraminiferal samples from another less comprehensive sequence of Lower Tertiary strata were collected during the years 1947, 1948, and 1949 in the region of Devils Den.

The prepared samples were studied during the years 1947–1952 in the Department of Paleontology at the University of California under the direction of Dr. Robert M. Kleinpell. Subsequent work both in the field and laboratory has been directed toward obtaining as complete and chronologically diagnostic a faunal sequence throughout the Lower Tertiary in the California province as possible.

Preliminary results of certain phases of the investigation have been presented from time to time at meetings of the Pacific Section of the American Association of Petroleum Geologists, San Joaquin Valley Geological Society, Cordilleran Section of the Geological Society of America, and the Northwest Geological Society (Mallory and Boyd, 1949; Mallory, 1953a, 1953b, 1954a, 1954b). This paper attempts a synthesis and revision of these reports and their conclusions, and the incorporation of many new data.

The majority of species known to be important in the Paleogene foraminiferal faunas are figured and their stratigraphic distribution in the California province is noted. In addition, an attempt has been made to draw any inferences from all kinds of fossil