Archive for the ‘oakland geology walks’ Category

The Skyline median trail

3 August 2015

My latest outing took me to what I’ll call the middle part of Skyline Boulevard, the part where the road is divided. Starting at Skyline High School and going south for about 2 miles, a footpath runs in the median. It’s a hidden gem. This is the nearest thing Oakland has to a long walk on a country lane.

mid-skyline-trail

Nobody online talks about this trail. I don’t know who made it or who maintains it. Cyclists laud the paved road, of course, which deserves the praise. The MBTR mountain bikers site reviews it under the name Skyline Boulevard Singletrack and gives it high marks, but you’d have to be as singleminded as me AND a mountain biker to seek it out. But the path is a nice way to enjoy this part of the hills.

This end of Skyline is exclusively on the Oakland Conglomerate, which holds up the spine of the ridge. Here’s the terrain:

mid-Skyline-topo

And here’s the geology, with “Ko” representing the Oakland Conglomerate (this is the same sequence seen in Shepherd Canyon):

mid-Skyline-geo

Some parts of the bedrock are straight sandstone.

mid-skyline1

But almost everywhere along the trail you’ll see the rounded cobbles that are this rock unit’s most distinctive feature, either embedded in stone or weathered out like this.

mid-skyline3

A slight detour up Brandy Rock Way will bring you to this fine exposure of the vertically tilted bedding, with a thick sandstone bed and conglomerate on either side (1000 pixels).

mid-skyline2

The road is slightly off the actual crest of the ridge, so the views it offers are mainly over the Bay. Here’s a spot near Cathy Lane overlooking a vineyard, the row homes across Leona Canyon on Campus Drive, the airport tower, the Bay and the San Mateo Peninsula.

mid-skyline4

I’m thinking that this would make part of a nice ramble. Farther south, Skyline merges into a two-way road and the path continues alongside it. Later this summer I’ll get to that part.

Rocks of the Skyline High neighborhood

6 July 2015

Walking the hills around Skyline High School makes for a nice workout, and there are some rocks, including serpentinite, the Joaquin Miller Formation and the Oakland Conglomerate. Here’s the Google Maps topography with the photo locations.

skyline-redwood-topomap

And the corresponding geology.

Skyline-redwood-geomap

The neighborhood centered on Balmoral Drive has lovely views, but few visible rocks. This is looking west to the Serpentine Prairie and beyond.

Balmoralview

But at the very end of Tartan Way we behold some mixed shale and mudstone of the Joaquin Miller Formation (Kjm).

JMF-tartanway1

JMF-tartanway

The area is mostly underlain by the Oakland Conglomerate (Ko), but the only glimpse of it you’ll see is on the high school grounds behind a fence.

Ko-SkyHigh

I think that the rocks here were examined during the construction of the homes in the late 1960s(?), because the strike-and-dip symbols are all located off the road, presumably in the excavations.

Now we’ll cross Skyline and explore the loop formed by Fernhoff and Bacon Roads. I particularly wanted to see this because it exposes the last bit of Oakland’s serpentinite I hadn’t yet visited. And at the entrance to Fernhoff Court, here it is.

serpFernhoffCt

The westernmost appendix of Bacon Road also dips into it.

serpBacon

But just uphill on Bacon, there’s some nice bits of Joaquin Miller again.

JMF-Bacon

The best place to see the Oakland Conglomerate is on Skyline Boulevard, specifically along the footpath in the median. Some places it’s well-bedded sandstone . . .

Ko-Skyline2

. . . and other places expose the classic deep-brown conglomerate with its well-rounded river cobbles.

Ko-Skyline1

There’s more along the roadside, but that’s probably not safe to visit. People drive fast here.

Ko-Skyline3

Thank goodness for the path in the median! It’s a nice amenity.


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