William B. Travers, 1972. "A Trench off Central California in Late Eocene-Early Oligocene Time", Studies in Earth and Space Sciences, R. Shagam, R. B. Hargraves, W. J. Morgan, F. B. Van Houten, C. A. Burk, H. D. Holland, L. C. Hollister
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An oceanic trench probably existed off central California in early and middle Cenozoic time, according to recently published interpretations of marine geophysical data. After allowance for late Cenozoic displacement along the San Andreas fault, a comparable part of onshore California was studied to determine if the geologic record there is compatible with these interpretations. Accumulation of mud at abyssal depths, chaotic deformation of sediments, the development of a submarine valley, thrust faulting, and basaltic and andesitic volcanism apparently all took place during late Eocene and early Oligocene time. Thus, onshore data support the concept of a late Eocene-early Oligocene trench. However, none of these phenomena occurred earlier in Cenozoic time in central California except the development of submarine valleys. Therefore, onshore data do not point to the presence of a trench off central California in Paleocene or early and middle Eocene time.