Abstract More than 6 ½ billion barrels of oil have been discovered in the San Joaquin Valley. Approximately 4 ¼ billion barrels have been produced and there is a reserve of 2 ¼ . billion barrels. San Joaquin Valley oil fields account for 42 per cent of the annual production, and contain 45 per cent of the reserves of the state. Ninety per cent of the oil produced to date has come from rocks which are Miocene or younger in age. Nonmarine sediments, largely of Miocene or later age, have accounted for 1 ½ billion barrels of oil, or 35 per cent of the total production of the valley. Oligocene and Eocene reservoirs are assuming importance as deeper drilling is done and new areas are explored. The pre-Tertiary sediments have accounted for less than one per cent of the oil produced. However, Cretaceous rocks are now being actively prospected. The San Joaquin Valley is a synclinorium some 250 miles long and 50–60 miles wide, lying between the Sierra Nevada Mountains to the east and the Coast Ranges to the west. The maximum depth to the basement is estimated to be in excess of 30,000 feet with the thickest sedimentary section being on the western side of the valley. Oil production is confined mainly to the southern portion which contains a thick section of organic Tertiary sediments. The San Joaquin Valley does not lend itself well to the basin analysis suggested by authors. The geosynclinal trough is present, as is the Sierra Nevada foreland to the east. Numerous faults of minor displacement along the east side of the valley might be termed a "hingebelt" but they interrupt the regional dip in only a minor way. The San Andreas and other faults of large lateral displacement have probably altered or removed the "geanticlinal welt," if it ever existed, on the west side of the valley. Furthermore, the western boundary of the valley has been transgressed many times by Tertiary seas making it difficult to determine the exact outline of the San Joaquin "basin." In the San Joaquin Valley, oil is found in almost every type of trap. Anticlinal structures with complications either by faulting or stratigraphic changes have accounted for the major volume of production. Examples of this type of accumulation are fields on the Coalinga-Kettleman Hills anticline, the Elk Hills-Coles Levee anticline, the Rio Bravo-Greeley trend, the Wheeler Ridge-Tejon Ranch anticline and the Belridge anticline. Oil occurs in faulted homoclines on the east side of the valley at Round Mountain, Kern Front, Fruitvale, Mount Poso, and Mountain View. Sands open to outcrop but with low fluid level produce at East Coalinga. The Lakeview area of the Midway-Sunset field appears to be synclinal. Although sand is the reservoir rock for 95 per cent or more of the fields, significant accumulations also occur in fractured shales at Elk Hills and Buena Vista Hills and in fractured schist basement at Edison. Inclined water tables have been noted in the Coalinga Nose, North Dome of Kettleman Hills, Paloma, Coles Levee, Elk Hills, and other fields. Advocates of the hydrodynamic theory are opposed by those who consider such inclined water surfaces due to differences in permeability. In some cases water encroachment is opposed to direction of inclination. In the future, stratigraphic and fault traps should account for a larger percentage of oil discovered in the San Joaquin Valley than in the past. Obscure structural highs revealed by subsurface geology, detailed geophysics, or other methods will undoubtedly contribute future discoveries. Recently, extensions and deeper drilling of known structures have accounted for substantial amounts of new oil and should continue to do so in the future.

Abstract 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.

Abstract A total of 675 billion cu ft of natural gas was produced in California during 1964, approximately 57 per cent of which was wet gas from 182 fields in all of the major oil-producing basins of the state; 43 per cent was dry gas from 93 fields, primarily in the Sacramento and northern San Joaquin Valleys (Fig. 1). Accumulations are found in a variety of structural and stratigraphic traps. Cumulative production to the end of 1964 was 20.7 trillion cu ft, four-fifths of which was wet gas. Reserves were estimated at approximately 10 trillion cu ft. Outstanding among the state's gas fields are Kettleman Hills, in the San Joaquin Valley, with a cumulative production of 2.59 trillion cu ft of wet gas; and Rio Vista, a dry gas field in the Sacramento Valley, which has produced 2.26 trillion cu ft. Other fields with cumulative production exceeding 1 trillion cu ft are Ventura in the Ventura basin and Long Beach in the Los Angeles basin.