Archive for February, 2009

Knockers south

26 February 2009

knockers

Now is a good time to post this picture taken last June, if only to remind myself that summer will return. This is looking up from Moraga Road, near the Piedmont maintenance yard, at the open land south of Mountain View Cemetery, and of course we are looking once again at knockers.

It’s a scramble to reach those rocks, but they promise the peace of a well-earned private perch with a great view. One or two of the rocks on this slope are appreciated by the local youth, to judge by the paint and other signs. Having been such a youth myself, I can’t object.

Just up the road from this spot is a sweet, discreet trail connecting to Abbott Way.

trail

The 40th Street cut

18 February 2009

roadcut

Apparently there are people besides me wandering my neighborhood and seeing the vanished past. This image comes from the 40th Street Cut blog, the record of an effort to put together an art show inspired by the Piedmont Avenue neighborhood. I have to say these guys know what grabs me.

The Key Route used to cut through the ridge running east of Broadway between Macarthur and CCA (which I’ve called Montgomery ridge, but on an old map it’s called Thermal Hill). This photo shows that cut before the tracks were pulled up and the cut filled in again. If I only had an hour to examine its walls!

The walls of the cut are steep, but there was no bedrock in it—that’s why the cut was made, because the work was easy. The material of the hill is stiff, well-compacted alluvium from a large, ancient fan that has had gulches cut into it by modern streams. Here the ridge was flanked by the two branches of Glen Echo Creek, one running along Broadway from the Claremont golf course and the other coming down from the cemetery grounds. (They join along Richmond Boulevard just north of 30th Street.) There was no danger of landsliding or rockfalls.

Geologists love roadcuts. In this part of Oakland they’re quite rare.

Oh—the 40th Street Cut people are having an opening reception Thursday the 18th, downtown. Details on the blog.

Vantage Point Park

15 February 2009

vantage point park

This tiny park is at East 12th Street and 13th Avenue, on a low rise next to a lot of activity. Between here and the water—Brooklyn Basin, the innermost part of Oakland Inner Harbor—run East 8th Street, I-880, Embarcadero Street, BART and the Southern Pacific rail line, plus I’m sure a number of underground power and water lines and what not. It’s a highly concentrated lifeline corridor. Across the way is the Coast Guard base on Government Island. In the distant left corner in the 800×600 version (click the image) you can just see Alameda Island. Except for the hummock in the foreground, everything visible is made land, artificial fill, with a high water table. It was created more or less haphazardly starting a century ago, and under strong shaking a lot of old fill of this type is prone to liquefaction.

Past the left edge of this photo, a little buried creek valley running down 14th Avenue reaches the bay. It’s all filled in, too. All the crowded life lines I mentioned cross that creek bed. In the next big Hayward fault earthquake, this is a highly vulnerable spot.

I took this shot on 19 November 2008 during a walk I took the length of Oakland, from the San Leandro to the Ashby BART stations. Lots more photos from that day on my Fotothing site.

The Oakland Conglomerate

7 February 2009

oakland conglomerate

The Oakland Conglomerate extends from Montclair, a little north of Snake Road, south along the whole southern end of Skyline Boulevard and beyond Lake Chabot to the northern outskirts of Castro Valley. It’s part of the Great Valley Complex, a huge sedimentary pile spilled off the ancient Sierra/Klamath ranges in Late Cretaceous time, specifically the Turonian and/or Cenomanian ages (about 90 to 100 million years ago). This may be its northernmost exposure, on a fire road across from the Shepherd Canyon fire station where a basketball court has been cut out of the hillside. I brought home some samples and hope to have fun with them soon.

oakland conglomerate

What’s cool about this rock unit is that the big clasts are almost all cracked or shattered or dinged up. That doesn’t happen to these potato-sized chunks of quartzite and granite in riverbeds or the seashore, where the stones were originally shaped. Researchers at Cal State East Bay have argued that they were damaged by thousands of earthquakes on the Hayward fault as they lay buried some 5 kilometers down.

This rock unit is actually mostly sandstone, especially the farther south you go. It crops out all the way down to the Alum Rock area.


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