Oakland Geology

Up in Huckleberry Botanic Reserve my eye was caught by a stone in the path—a clast of Claremont chert, to be exact—bearing this fine example of a slickenside. Slickensides are the polished, striated surfaces on a rock that result from rubbing together, usually by movement along a fault or, in this case, by internal deformation when the rock was being squeezed and uplifted into the Oakland Hills. Little ones are more common than you might think, but ones the size and quality of the one in San Francisco’s Corona Heights are exceedingly rare. I shot this one because there aren’t a lot in the Claremont chert. Usually deformation is accommodated in the shaly beds between the cherty layers, so there’s little chance to get a good rubbing going. The bluish color is reflected skylight, not the chert itself.

This entry was posted on 19 January 2009 at 10:58 pm and is filed under Oakland chert. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.