A Summary of the Remarkable Geology of the Pine Mountain Club Region

A Summary of the Remarkable Geology of the Pine Mountain Club Region—in 45 Minutes, More or Less
Thomas L Davis Geologist, Geologic Maps Foundation, Ventura, California

The Pine Mountain Club (PMC) area lies at the crossroads of some of California's most fascinating geologic features. This presentation provides a nontechnical introduction to the local geology and its geologic history, beginning with the San Andreas Fault, one of the world's most studied active plate boundaries. Approximately 300 kilometers (185 miles) of right-lateral strike-slip movement along the fault during the past 20–30 million years has profoundly shaped the regional geology, with the 1857 Fort Tejon earthquake representing the most recent great rupture in this area. PMC lies within the western Big Bend segment of the fault, near its intersections with the Garlock and Big Pine faults, both of which have also played important roles in the region's geologic evolution.
South of the San Andreas Fault are the ancient metamorphic and granitic rocks of the Mount Pinos massif, which overlie the Pelona Schist along the Sawmill Mountain thrust, a paleo-plate-boundary fault formed during subduction of the Farallon Plate approximately 50–70 million years ago. To the southwest lies the younger Cuyama Basin, which preserves a sedimentary record ranging from nonmarine deposits to deep-marine strata and contains the once highly productive Russell Ranch and South Cuyama oil fields. North of the San Andreas Fault are the granitic and metamorphic rocks of the Blue Ridge–Tejon Ridge area, considered the southernmost exposed extension of the Sierra Nevada crystalline basement. Directly north of the Ridge lies the tectonically active fold-and-thrust belt of the San Emigdio Mountains, where north-south crustal convergence has folded and faulted sedimentary rocks of the San Joaquin Basin into the large anticlines, synclines, and thrust faults exposed within the Wind Wolves Preserve.

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Although mining has never been a major industry in the Pine Mountain Club area, exploration for gold, silver, iron, and antimony has contributed to the region's colorful human history.