The Sacramento Valley province covers an area of 11,578 square miles in the northern part of the great interior valley of California. The eastern part is underlain by a complex series of Paleozoic and Mesozoic metamorphic and granitoid rocks, and the western part is underlain by tightly folded and partially metamorphosed sediments and basic intrusions of Jurassic age.

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About 44,000 cubic miles of unaltered sediments, ranging in age from Lower Cretaceous to Pliocene, occupy the basin. Of this volume, three-quarters is marine Cretaceous, and the remainder is marine Eocene covered by a veneer of non-marine Miocene and Pliocene rocks.

More than 300 exploratory wells have been drilled in the province, resulting in the discovery of 28 commercial gas pools, from which more than 1¼ billion M.c.f. of gas had been produced by December 31, 1949. The average explored density is 38 square miles per exploratory well with the greater concentration in the southern part.

Producing zones range in age from Pliocene to Upper Cretaceous. Eocene sediments have furnished the major part of the production. Anticlinal closures are the predominant type of discovered trap with minor accumulations due to fault closures and stratigraphic discontinuities.

Oil seeps in the outcrop and oil showings in Lower Cretaceous sediments in shallow wells in the western part of the province suggest the possibility of undiscovered oil reserves. Additional gas reserves, resulting from deeper and more intensive drilling are a distinct possibility.

The variable distribution of formations and sand facies within the basin, together with the regional eastward overlap of Middle and Lower Cretaceous sediments, suggests that some type of stratigraphic trap may be instrumental in the accumulation of the major part of the discoverable reserves in this province.

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