The Cuyama Valley, lying in the Coast Ranges midway between the San Joaquin and Santa Maria districts, was established as a commercial oil producing province by the completion of Richfield Oil Corporation's Russell No. 28-5, on June 13, 1948. This new field is known as the Russell Ranch oil field. It is situated in the western portion of the valley and is producing from Lower Miocene sands on fault closures. Previously less than a dozen holes and one small producer from upper Miocene sand (Norris Oil Company's Cuyama No. 2) had been drilled in the valley.

Geologically the Cuyama Valley, between the Caliente and San Rafael uplifts, comprises granitic basement and Cretaceous to Pliocene strata folded and faulted in east-southeast trends. Eocene strata are present only in the eastern part of the valley, the Oligocene (?) is a red bed facies, 5,000 feet of lower Miocene sands pinch out southwestward, marine Miocene shales and sands grade eastward into red beds and the Pliocene strata are entirely non-marine.

Initial production of the discovery well, Richfield Oil Corporation's Russell No. 28-5, was 508 barrels per day, flowing, 38° gravity oil, from the interval 2,970-3,360 feet. This interval is lower Miocene and has been designated the Dibblee zone. Five days later another pool was established 2¼ miles northwest by completion of Richfield Oil Corporation's Anderson No. 37-30, flowing 3,041 barrels per day, 33.5° gravity oil, from the interval 2,800-3,019 feet, also lower Miocene. The former, named the Russell area, had on October 1, 1948, eight completed wells with initial rates to 2,500 barrels per day, and maximum sand interval of 350 feet. The latter, designated Whiterock area, had nine completed wells with initial rates to 4,000 barrels per day, and maximum sand inter al of 480 feet. Also, on October 1, 1948, the Russell Ranch field has eight active development wells, while eight wildcats were drilling at locations as far as 9 miles from production.

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