Archive for October, 2012

Tunnel approach

31 October 2012

I’ll be taking a tour of the new Caldecott Tunnel bore on Friday. This is the view of Route 24 from the ridge south of it, across from Hiller Highlands. Everything here is east of the Hayward fault.

great valley

On the right is uppermost Broadway, where a line of locals and advanced commuters chronically hope for a few seconds’ advantage by merging at the last second before the tunnel. I’ve decided that it’s faster to get in the left lane of 24 as soon as possible and stay there. Anyway, all the land from here to the far curve is underlain by rocks of the Great Valley Complex, of Late Cretaceous age. A fault separates it from the Sobrante Formation behind it, which is much younger. The lower part of the skyline ridge is Sobrante, but the high part is chert of the Claremont Shale. The tunnel penetrates both of those units, and I hope for a good look at it.

I was standing by the power line; you get to it by hiking down the road from the sports complex, on Broadway at the overcrossing, or by ducking around the gate at the top of Pali Court. The Great Valley here is a mix of fine-grained sedimentary rocks. Exposures are poor and the fabric is disrupted. Here’s an exposure on Pali Court.

great valley

And here’s a closeup from nearby.

It’s very shaly. The lenses of more siliceous stuff don’t add to its strength.

Fault valley

21 October 2012

October 21, not October 17, is Oakland’s real Earthquake Day. While many of us remember the 17th vividly, the day of the Loma Prieta quake in 1989, the morning of October 21, 1868 was when the original Great San Francisco Earthquake struck. It was on this side of the bay, on our own earthquake fault, and the ground cracked from Fremont all the way to the edge of this view from the end of Pali Court, in the neighborhood just across route 24 from Lake Temescal.

hayward fault valley

The Hayward fault runs from the notch on the skyline, which is in Montclair, to the right edge behind the house in the middle distance. This part of the fault, between Mills College and Lake Temescal, is the only place that has large areas of bedrock on both sides. What that means for the purposes of today’s post is that it’s the most rugged and picturesque part of the fault and has probably the greatest concentration of million-dollar homes.

Today I invite you to review this blog’s category “the hayward fault.” I seem to have rattled on at great length on this subject. Some day the fault will rattle all of us at great length.

Today’s Oakland Tribune has an article about newly mapped faults in the Hayward fault zone; I won’t link to it because the Trib’s links die quickly. But the new Alquist-Priolo zone map can be accessed here.

Calmar, Mandana, Longridge

7 October 2012

I’ve been exploring the surprisingly intricate topography between Lakeshore Avenue and Park Boulevard, where I count four separate ridges separated by three valleys. From the ground, it’s a challenge to visualize and photograph. This is the view across Mandana valley from the side of Calmar ridge, on Santa Ray Avenue, to Longridge.

longridge

I haven’t forgotten the blog, I’m just real busy. The weather lately has been superb for walking.


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