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