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Abstract: Geology of the Palos Verdes Hills, California

DIBBLEE JR., THOMAS, University of California, Santa Barbara Dibblee, Thomas W., Jr., Santa Barbara, CA; HELMUT EHRENSPECK, Dibblee Geological Foundation, Santa Barbara, CA

The Palos Verdes Hills are an island-like terrain of rolling hills between the Los Angeles Plain and the Pacific ocean, with a northwest-trending subdued summit as high as 500 m. These hills expose about 600 m of marine biogenic shale of the medial to late Miocene Monterey Formation on Mesozoic(?) bluechist basement. This shale is composed of the Altamira siliceous shale, 400 m thick, that includes a basalt unit near the base, and the Valmonte Diatomite, 200 m thick, at the top. Along the northeast foothills this biogenic formation is overlain by the Malaga Mudstone, late Miocene, then in places, by a mudstone remnant of the Fernando Formation, Pliocene, and unconformably by onlapping Pleistocene deposits, including the San Pedro Sand. These post-Monterey units are in large part covered by onlapping older alluvium and dune sand.I

N the adjacent Los Angeles basin, including the Torrance oil field, the Miocene sequence (called Puente Formation) likewise overlies blueschist basement and is about 600 m thick, but is more clastic, with several sandstone intervals. It is overlain by about 600 m of Pliocene Fernando claystone, overlain by about 300 m of Palos Verdes Sand.

Structurally the Miocene sequence of the Palos Verdes Hills is gently undulating along northwest-trending axes, but overall is anticlinal, with a slight southeast plunge. This structure is elevated against the flat-lying structure of the Los Angeles basin along a steeper northeast dip and partly on the active(?) Palos Verdes fault that is largely obscured by Pleistocene deposits.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California