Archive for September, 2012

The five-year mark

25 September 2012


On this day in 2007, I launched Oakland Geology with a photo of what happens when Oaklanders build without geological awareness. Since then I’ve made plenty of posts along the same lines, but geology is not a one-note subject. Most of the time I’ve celebrated what intrigues and tantalizes me about this remarkable city’s natural underpinnings, always with a photo to share.

In 2010 Oakland Geology was named Best Blog about East Bay Rocks. (I really should get myself over there and pick up my plaque.) This week I learned that one of our celebrated local authors, Michael Chabon, cited Oakland Geology in the acknowledgments of his newest book Telegraph Avenue. These are signs of what I always hoped to achieve with the blog: to extend popular awareness of this city’s place in deep time and its deep present, to include our rocks and soils and landforms and geologic forces in the everyday conversation that is constantly weaving our future.

This blog, more than all my other writing, has brought me face to face with interested Oaklanders, who appear to be roused enough by these snippets and snaps to come see me wave my arms, with Powerpoints or vistas behind me, and dump more data on their heads in person. I appreciate your audience and your readership. Long may we continue to wave.

Pershing knob

9 September 2012

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.


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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