Abstract

Recently-drilled wells in the Chaffee Canyon oil field, Ventura County, California, reveal that the Wiley Canyon producing anticline formed in the Pleistocene prior to much of the displacement on the Oak Ridge fault. The east and west plunge in part predates deposition of the Vaqueros Formation of early Miocene age. The anticline changes trend from S70°W in the west to S80°E in the east. The dip on the south strand of the Oak Ridge fault increases eastward across the field from 70–75° to 83–65°; farther east, the fault plane is overturned and dips north. The Torrey fault can be traced northwest under a landslide east of Wiley Canyon anticline, but not farther northwest. Production in the Chaffee Canyon field is primarily from marine sands more than 145 m below the top of the Eocene Llajas Formation. Many oil fields producing from Oligocene and older reservoirs south of the Oak Ridge fault have a proto-structure that existed during the Miocene, when geothermal gradients were high. At first glance, the Chaffee Canyon oil field appears to violate this rule because the Miocene section is much thicker there than at Torrey Canyon field to the east and Shiells Canyon field to the west. However, the evidence for a pre-Vaqueros broad fold seen on an east-west longitudinal cross-section suggests that a low-relief anticline did exist at Chaffee Canyon, possibly with a trend oblique to the younger Wiley Canyon anticline.