Here’s a deeper look at the local bedrock. The hill on which Piedmont and its surrounding neighborhoods sit is held up by a body of Franciscan rocks, roughly 100-150 million years old. It’s mostly sandstone, as shown in the Dracena Park quarry pit, and mélange, as shown in the Mountain View Cemetery grounds. But the huge Franciscan Complex consists of a subset of nine different bedrock packages or terranes. Oakland’s Franciscan inventory is part of the Novato Quarry terrane, named for (of course) its exposure in a quarry in Novato. But here in Oakland is its southern end (I’m pretty sure). The terrane stretches from here to Bodega Head in a discontinuous string across the structural grain of the land. This view (click full size), from Dwight Canyon, shows other outposts of the Novato Quarry terrane, with Albany Hill (“el cerrito”) in front, then Point Richmond, and at rear right the rocks of Novato itself and Big Rock Ridge beyond. Another locality is Point San Pablo. To the west of it is the Marin Headlands terrane, which is self-explanatory.
What strung out the rocks of these terranes was movements on the various parts of the San Andreas fault system, which has sliced and spread out the pre-existing geology that was compiled during hundreds of millions of years of straightforward subduction.