ABSTRACT Opal-CT grade siliceous, calcareous, and organic rocks of the middle member of the Miocene Monterey Formation are seasonally well-exposed on the wave-cut beach platform at Ellwood Beach, Santa Barbara County, California. These rocks display a variety of structural deformation mechanisms including bedding-plane slip, thrust faulting, high-angle reverse faulting, and folding, which are common to most of the exposures along the Santa Barbara County coastline. Detailed stratigraphic measurements provide possible correlations to other coastal exposures of southern Santa Barbara County.

ABSTRACT Elwood oil field in Goleta, California, was one of the first oil fields in California to commercially produce oil from the lower Miocene Vaqueros Formation. Discovered in 1928 by field mapping, the oil field reached its peak production in 1930. The eastern part of the oil field straddles the shoreline, extending eastward onto Ellwood Mesa and westward into the offshore. The 1944 extension to an adjacent, connected structure offshore about 3.5 km (2 mi) west of the discovery well nearly doubled the size of the field. Prolific early wells were due to high porosity, high permeability, and an active water drive in the primary reservoir. Overproduction in the 1930s led to premature water encroachment in the eastern area and depletion prior to discovery of the western area. The subsurface structural trap is a gentle, open, east-west trending, fault-bounded anticline or elongated dome, with a shallow central saddle and both east and west closure. This structure is relatively simple compared to the complex faulting and folding of the Miocene Monterey Formation exposed on Ellwood Beach above the oil field. The disparity of structural styles between the subsurface and surface partly reflects the disharmonic nature of Monterey Formation deformation. Additionally, the structures on Ellwood Beach are related to the fault block which lies above and south of the Elwood oil field.