Abstract Cuyama Valley, in the southeastern part of the Salinas-Cuyama Tertiary basin of the southern Coast Ranges of California, contains the major Russell Ranch and South Cuyama oil fields, which have produced respectively over 40 and 67 million barrels of 35 0 A.P.I.-gravity oil from unitized and pressure-maintained reservoirs since mid-1948 and mid-1949. Production from the fault-trapped reservoirs is derived respectively from 290 and 480 feet of Vaqueros (lower Miocene) sands at depths ranging from 2,800 to 4,300 feet; productive areas comprise 1,400 and 2,500 acres. In addition, there are three minor fields in Cuyama Valley. San Ardo, the only other major field, is located in the northwestern portion of the Salinas-Cuyama basin. This field produces 11.3 0 gravity oil from upper Miocene sands at depths of 1,800 to 2,400 feet, from an area of about 4,000 acres. Cumulative production to July 1, 1956 has been 50 million barrels. The Salinas-Cuyama basin, which is approximately 160 miles long and 28 miles wide, is bounded on the northeast and southwest by the San Andreas and Nacimiento fault zones, respectively. It is underlain by granitic basement and contains up to 7,000 feet of lower Miocene marine clastics. In the Cuyama portion of the Miocene basin a thick continental section grades southwestward into a very thick shallow-water marine section composed principally of deltaic sands. These, in turn, change rapidly southwestward to a thin section of marine organic shales and sands of the oil-producing, moderately shallow-water belt, which thins rapidly southwestward. These sharp thickness and facies changes are accentuated by reverse faults of probable Quaternary age. Locally these faults have a prominent strike-slip component of displacement and conceal at least one important, old and steep lateral fault which further accentuated the stratigraphic changes. The original Salinas-Cuyama Miocene basin has been elongated many miles by cumulative movements on northwest-trending right lateral-slip faults which now juxtapose formerly widely separated sedimentary facies. In Cuyama Valley, one of these is the buried Russell fault which traps most of the oil, and another probable one, aided by reverse faulting, explains the close proximity of thick deltaic and thin basin facies.

Abstract The Central Coast Ranges are situated between North Latitudes 34° 41′ and 38° 3′ and West Longitudes 119° and 122° 30′ extending from San Francisco on the north to Ventura County on the south and embracing the following minor basins: Livermore, Halfmoon Bay, Salinas Valley, San Andreas Trough, and the Cuyama Valley. The total area of sedimentary rocks is approximately 4,500 square miles and their estimated volume is 6,500 cubic miles. About 75 per cent of the sedimentary rocks are marine. The generalized geologic map (Fig. 25) shows the thickness of the sedimentary section that is favorable for oil and gas generation and accumulation. In the area west of the San Andreas fault the basement is predominantly granitic but locally the top of the Cretaceous, where present, is considered as basement due to the intensity of deformation and the lack of good source and reservoir beds in the formations of this age. East of the San Andreas fault the top of the Franciscan formation is considered as basement and the overlying Cretaceous is included in the sedimentary section favorable for oil and gas accumulation. This classification is arbitrary but is the most convenient for constructing an isopach map of this type. The Cuyama Valley, which was barely mentioned as a possible future oil province in the symposium of 1941, has now developed into a major oil-producing province. Subsequent to the first commercial oil strike in January, 1948, in a Norris Oil Company well producing 150 barrels per day of 22°

Sedimentary basins within the Transverse Ranges and adjacent areas of Southern California are truncated by several branches of the San Andreas fault system. Comparison of basement and sedimentary successions of the Lockwood Valley-Cuyama Valley area with those of the Soledad Basin and western San Gabriel Mountains indicates that these districts have been separated by right-lateral slip on the San Gabriel and Sierra Madre faults. Right-lateral slip on the San Gabriel fault system may have been accomplished in two phases: (1) an interval of relatively rapid slip to account for 20 to 30 km of offset beginning in late Barstovian or early Clarendonian time and (2) a second interval to account for 18 to 28 km of offset after Clarendonian time. For the second interval, it is not possible to determine whether most of the offset occurred gradually throughout Hemphillian time or took place during some part of it. There may have been as much as 9 km of post-Hemphillian slip on the San Gabriel fault system. This post-Hemphillian interval, about the last 4 to 5 m.y., corresponds to the opening of the Gulf of California, so that it appears that most of the 48 km of right-lateral slip on the San Gabriel fault system had been accomplished prior to then. Post-Hemphillian slip on the San Gabriel and Sierra Madre faults appears to have been distinctly less than for other elements of the San Andreas fault system. None of the branches of the San Andreas fault zone east of the San Gabriel fault appears to have undergone more than about 20 to 30 km of right-lateral slip during or after Hemphillian time, or during the past 10 m.y. or less. Even including 24 km of right-lateral slip on the San Jacinto fault zone, the aggregate slip on the San Andreas fault system during this time appears to be on the order of only 60 km, substantially less than required to compensate for the 250 km involved in the opening of the Gulf of California during the past 5 m.y. If the Pinto Mountain fault is the eastern equivalent of the Malibu Coast–Cucamonga fault zone, essentially no right-lateral slip occurred on the San Gabriel fault from the Saucesian through the Luisian interval; east of the San Gabriel fault, essentially no slip occurred on the San Andreas fault from Saucesian through Mohnian time. This reconstruction is compatible with the range of slip on the San Andreas system proposed by Baird and others (1974). It also suggests that about 20 km of post-Eocene(?) slip occurred on the Punchbowl-Nadeau fault prior to Zemorrian time. If the Pinto Mountain fault is not the eastern equivalent of the Malibu Coast–Cucamonga fault zone, and if the only slightly offset pre-Tertiary basement structures cited by Baird and others (1974) are merely fortuitous, there may have been more extensive pre-Hemphillian slip on the San Andreas system, as envisioned by Ehlig and Ehlert (1972) and Crowell and Walker (1962). This slip would be comparable in magnitude but not in timing with the 250-km slip associated with the opening of the Gulf of California.