Pershing knob

Pershing Drive sits at the top of the south end of the Piedmont block at nearly its highest point, just under 800 feet. At one end of the road is a long exposure of rugged Franciscan chert that is exquisitely integrated into the landscaping, which includes native oaks as well as the usual plantings. It is a challenge to photograph but a delight to see in person.

chert

This is the high-grade, bleached and sometimes greenish banded chert of the Piedmont block rather than the beautiful red ribbon chert of the Marin Headlands. Its outcrop appears on the Oakland geologic map east of Piedmont’s Tyson Lake. The very steep slope on its bayward side is interpreted as a thrust fault separating the higher Franciscan melange from the lower Franciscan sandstone. Melange is not generally considered a strong stone by geotechnical engineers, but recent research shows that it depends. This melange is the best bedrock in Oakland, and worthy of its gracious and picturesque neighborhood.

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