A thick Miocene marine basinal succession, dominantly sandstone, underlies the southern portion of California's San Joaquin Valley. Deposited in paleontologically defined depths of as much as 5,000 to 6,000 feet, the sands are pebbly and gritty to fine grained, largely angular, poorly sorted, often silty and micaceous, quartzose to arkosic and are interbedded with dark carbonaceous shales. Graded bedding is common and in conjunction with depth estimates is taken to imply turbidity current origin for most of the sands.

Early Miocene turbidites spread far southwestward from the Sierra Nevada provenance, but by late Miocene, anticlinal barriers, rising from the sea floor, restricted the turbidites, including the highly productive Stevens sands, to the northeastern side of the basin. These late Miocene sands at first entered from discrete troughs or canyons but later from more widely dispersed sources as shelf sands encroached. Deep basinal transport seems to have been axially northwestward. Locally, thick Stevens synclinal channel sands spread eastward off the rising Temblor Range. Sudden cessation of basinal sand deposition was followed by deposition of chert, shale, and Pliocene neritic sediments.

Detailed subsurface correlations show that Stevens sand bodies include sinuous channel fills bounded by major anticlines, sands flanking and covering lower structures, and lobate and branching apron sands in simple homoclinal areas. Compaction structures are shown to control some accumulations and offer clues for continuing exploration.

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