This report is a result of recent studies of the Cenozoic stratigraphy and structure of the San Joaquin Valley that were directed at Cenozoic depositional and tectonic history. Most previous work on the Cenozoic has focused on the Quaternary surficial deposits and on the outcrops of older rocks at the margins of the valley, although ground-water resource studies of the upper Cenozoic deposits have used subsurface information (for example, Davis and others, 1959; Croft, 1972). One purpose of this report is to show the distribution and stratigraphic relations of Tertiary units under the valley and represents, in part, an attempt to extend correlations from Tertiary units previously recognized in outcrop at the margins of the valley into the subsurface. A second purpose is to depict the structure of the Tertiary rocks by cross sections and by a structure contour map of a middle Tertiary horizon.

The emphasis in this report is on the Tertiary rocks of the northern part of the San Joaquin Valley, although pre-Tertiary stratigraphic units are shown on the cross sections where information was available. They serve to emphasize the discordance between the Neogene and the older units. Correlations of units in the Great Valley sequence (Late Jurassic to earliest Tertiary) are based mostly, with some modification, on the work of Hoffman (1964) and Callaway (1964), although the informal stratigraphic names used by those workers are not applied here.