Walk number 28 in Charles Fleming’s Secret Stairs East Bay winds around the fine homes and hills of Piedmont along the valleys of Wildwood and Bushy Dell creeks. Here’s the route, shown on the Google Maps topo base.
The first and last part of the loop is in the watershed of Wildwood Creek while the rest is in the Bushy Dell Creek watershed. (They run down Lakeshore and Grand Avenues respectively, separated by Warfield ridge, and combine down at Lake Merritt where their names are sunk in bronze by the pergola.) Geologically, the walk covers the uppermost part of the big Pleistocene alluvial fan and the edge of the Franciscan bedrock block that underlies most of Piedmont.
We start at the Lakeshore-Winsor split in the stream valley and make our way toward the divide. On Portsmouth Road the high ground of the bedrock zone stands out ahead.
At the far end is a steep climb to Wildwood Avenue, where we can look back across the stream valley to the ridge topped by Calmar Avenue, on the Oakland side of the city line.
Turning the other way, we look over the valley of Bushy Dell Creek. Once a large formal garden, this part of the valley was filled and leveled for its current use as a sports complex. It appears never to have been a quarry, unlike Dracena Park to the north or Davie Tennis Stadium to the south.
We turn upstream along the creek, where the land is relatively untouched. Just above this spot is the site of what was reputed as a sulfur spring.
The geologic setting doesn’t really give much support for the presence of a proper sulfur spring like the one in Walnut Creek, but after all this time the question is moot. Certainly I didn’t notice any odor. The grotto was very pleasant anyway, and there’s real bedrock all around. It’s mapped as Franciscan sandstone of the Novato Quarry terrane.
The route goes farther up and takes a loop past a pair of boulders.
Take a close look at these: they’re genuine Oakland-style blueschist, globs of old ocean crust that have been carried tens of kilometers down into the earth along a subduction zone, then spat back out, possibly more than once. (The details are at the bleeding edge of California geology.) The one boulder displays good color and mineralogy:
The other has some nice slickensides to show us.
Coming back downstream and past the baseball diamond, we pass the entrance to the football field. The view looks down the valley toward the lake and downtown.
Near here we can see more exposures of the sandstone bedrock, but soon afterward the route returns to the alluvial fan. The two substrates make subtly different topography, but that can be hard to see given the heavily landscaped landscape.
Palm Drive offers a picturesque farewell view of the Bushy Dell Creek valley.
Again we cross the divide between the two watersheds at Wildwood Avenue. The near valley is accentuated by glimpses of the higher hills.
I never get tired of this stuff.
Here’s the route in more detail.