Archive for August, 2008

‘Mount Ararat’, another Rockridge rock

27 August 2008

In my search for Rockridge Rock I’ve found some nice places. I consider the hillock embraced by Wilding Lane to be one, possibly even the Rock itself. One piece of lore that guides me is the fact that in the late 1800s, the Rock was easily reached from town and picnickers enjoyed an expansive view of the Bay and hills. The 1912 Oakland street map I rely on in my research labels the Wilding Lane hill “Mt Ararat.” Here’s the view from Wilding and Canyon View Lanes (click full size). If you strip away the trees and homes, the appeal of the place is obvious.

wilding lane view

Mount Ararat, unlike Cactus Rock near Acacia Avenue, is right next to the main drag of Broadway Terrace. Here’s a map to help you find the place.


The Crestmont serpentine patch

20 August 2008

crestmont serpentine patch

Every neighborhood in Oakland with a “mont” in its name has bedrock exposed. Crestmont is a good example. Most of the Crestmont neighborhood, north of Redwood Road and east of Holy Names University, sits on serpentine rock—more precisely, serpentinite. This is the biggest exposure, at the intersection of Crestmont Drive and Westfield Way. Below is an exposure just to the north (click full size), which is somewhat bluer than the blue-green of the main patch. I’ve shown pieces of this rock to local geologists, asking them “Is this serpentinite or blueschist?” They usually say “Beats me” or, even better, “Yes.” These rocks are not easily assessed by just eyeballing them.

crestmont blue serpentine

The open lot on the east side of Crestmont near Samaria Lane displays some splendid outcrops of this “lizard-skin” stone:

crestmont serpentinite

Eucalyptus Road Rock

12 August 2008

eucalyptus road rock

While walking the sidewalks of Oakland for my Oakland Sidewalk Stamps blog last week, I made a special trip to Eucalyptus Road, a short loop with each end in Berkeley south of Claremont Avenue. It’s the northernmost place in Oakland on the Piedmont block, better known as our lump of the Novato Quarry terrane. At the heart of the road, edged with eccentric brickwork (and some old sidewalk stamps, natch), is this sprawling property with lush grounds, old eucalyptus trees and a fine rounded knocker reigning over it all. (click full size)

Elsewhere on the street you’ll see a little more bedrock, too. Also, if you have an aversion to Berkeley you can get there via an unmarked, unmapped spur off uppermost Harwood Avenue.

The Novato Quarry terrane

8 August 2008

novato quarry terrane

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.