Coalinga Oil Field (Fig. 11) has been oil and gas productive from the Temblor Formation on Coalinga anticline and the contiguous homocline to the southeast since the early part of this century. Oil was first discovered in 1890 in the Oil City area in Upper Cretaceous strata, up-plunge from the present Coalinga Field (Anderson, 1952). Development of the Eastside and Westside Fields began in 1900 and 1901 respectively, close to the Oil City area, but soon spread north, south, and southeast to the limits of the field (Anderson, 1952). The producing area is divided into the Eastside Field on the crest and flanks of the plunging anticline, and the Westside Field along the homocline into the apex of the Coalinga syncline (Kaplow, 1945). Approximately 98% of oil production in the Coalinga Oil Field is from the Temblor Formation (Cal. Oil and Gas Fields, Maps and Data Sheets, 1960), although recent efforts have been directed toward the shallower Etchegoin Formation (Taschman, 1982).
Trapping is accomplished by a combination of structural and strati graphic mechanisms. The structural configuration of Coalinga anticline and its position up-dip from the Buttonwillow depocenter through much of the Tertiary (Zieglar and Spotts, 1978) resulted in migration of oil to the Coalinga Field. Zieglar and Spotts (1978) suggested that hydrocarbon generation occurred in Tertiary beds of the depocenter within the last few million years (perhaps 5 m.y.), but other structures “competing” for the oil, such as the Kettleman Hills, only developed during the Pleistocene episode of folding (Harding, 1976). The Temblor is overlapped by the Monterey and Etchegoin Formations along the Westside Field and is not exposed.