The Vernalis dry-gas field is on the west side of the Great Valley of California, 18 mi south of Stockton. It was discovered in 1941 by Standard Oil Co. of California as a result of a seismograph survey. One additional producer and one dry hole had been drilled by 1943. Subsurface studies led to renewal of activity in 1958 which resulted in the drilling of 32 additional gas wells and 23 dry holes in and around the field. Ten new producing zones have been found at depths ranging from 3,010 ft in Miocene beds to 4,952 ft in Cretaceous. Productive area now is approximately 3,500 acres.

The field is anticlinal in form, but stratigraphic factors greatly influenced accumulation and local variation in occurrence of gas. Deeper possibilities exist.

Many wells are completed in two or more zones. Initial open-flow potentials ranged from 3,000 to 28,900 Mcf a day. Annual production in 1964 was 7,343,901 Mcf. Cumulative production to December 31, 1964, was 48,612,799 Mcf. Original recoverable reserves are estimated to have been more than 100 million Mcf.