The South San Joaquin Valley section begins on the west side of the San Andreas fault where the strata consist of about 4,500 feet of continental beds, from Paso Robles through Simmler, resting on a granite Basement Complex. East of the San Andreas fault, the structurally complex Temblor Range has a thick marine section from upper Miocene through the Eocene and probably part of the Upper Cretaceous, although no wells have penetrated the latter. Eastward from the Belgian anticline, the wedge of marine Pliocene thickens into the central basin. On the eastside, the Pliocene becomes entirely continental. The Miocene also thickens basinward but with the exception of the top and bottom generally maintains its marine character eastward. The Oligocene is a thin sliver which is ov rlapped westward and lost in the general eastward sand and continental facies. Greatest penetration of the upper Eocene has been at Belgian anticline. On the eastside, the upper Eocene rests unconformably on the Jurassic Basement Complex; and along the east border, it becomes thin and continental and inseparable from the lower Miocene, Walker.

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The Central San Joaquin Valley section has been tied with the Salinas Valley section for reference and general comparison; although the stratigraphy across the structurally complex San Andreas fault and Diablo Range area is fragmentary. Here the Basement Complex is the Jurassic Franciscan series. East of Curry Mountain, the basal Pliocene unconformity overlaps the Miocene, Eocene and the top of the Upper Cretaceous. This marine series thickens basinward and changes to a continental series. Along this line of section, all the marine formations of the westside change to a continental facies on the eastside. The upper Miocene has maximum thickness of 2,100 feet and consists of marine shales and sands on the westside and central area. The middle and most of the lower Miocene, however, are dominantly continental in character. The lowermost Miocene or Zemorrian stage is represented by a thin marine wedge in the Guijarral Hills area. Along the central San Joaquin Valley section, in addition to the upper Eocene, the middle and lower Eocene, Paleocene, and Upper Cretaceous are present.

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