Oakland panorama

29 February 2016

Even though it’s called Leap Day, February 29 feels like a good day to stop and look around. Here’s a fine panorama from 10 February 2015, the first day I explored the Ridgemont neighborhood high above the old Leona Quarry (1200 px). The view is almost due south.

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Most of the California landscape is oriented like this, northwest-to-southeast, thanks to its plate-tectonic position between the North America and Pacific plates.

What are we looking at? Here’s an annotated version, with the following landmarks noted.

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1: Mission Peak, overlooking Fremont and San Jose.

2: Knowland Park hill with its green meadows.

3: Fairmont Ridge, overlooking San Leandro.

4: Loma Prieta.

5: Mount Umunhum and the spine of the Sierra Azul.

6: Coyote Hills on this side of the bay, Stevens Creek canyon on the other, where route 17 leads to Santa Cruz.

7: King Estates Open Space, looking its emerald best.

8: Black Mountain overlooking Mountain View (and hey what a coincidence).

All of these are great places to visit.

The red Vs mark the Hayward fault, left to right: at the foot of Mission Peak, in the saddle of Fairmont Ridge, in the Oakland Zoo and running down the valley of Arroyo Viejo past Holy Redeemer College.

Upper Knowland Park and the Chabot fault

22 February 2016

The upper part of Knowland Park is quite different from the lower part. I made a reconnaissance visit last week. Here’s the geologic map, along with white numerals indicating the localities I took the photos from or at.

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Whereas the lower part of the park (west of Golf Links Road) is dominated by Franciscan rocks and the Leona rhyolite, the upper part is mapped as completely sedimentary. My main destination was the saddle between the areas mapped as Joaquin Miller Formation (Kjm) and Knoxville Formation (KJk), where the obscure Chabot fault runs. Here’s a view of the saddle and the bare knob of Knoxville beyond it.

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The Joaquin Miller is a fine-grained sandstone here, sometimes with a slightly slickensided texture that makes it almost glossy.

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The roadbed displays it nicely. The saddle doesn’t display any obvious signs of a fault.

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But as you approach it, the honey-colored rock in the roadbed . . .

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. . . gives way to a deep sandy soil with chunks of strange rock floating on it. Not what I expected at all. I thought I’d see a hard, dark shale/conglomerate like what’s in the streambed of Arroyo Viejo. Instead it looked for all the world like a Franciscan assemblage. Here are a few of the stones.

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This last specimen, and the first, appear to be bits of the Leona rhyolite. So there is some complexity here that’s not recorded on the map, perhaps a splinter of Franciscan that got mixed up in here.

I didn’t learn much about the Chabot fault, except that the abrupt change in lithology is a sure sign of a fault contact. I’ll have to do more poking around before I can write something coherent about it. (In fact, please ignore site 4 on the geologic map; I’m not showing that this week.) This is the view south from point 3 along the valley that marks the fault trace (1000 px).

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And here’s your weekly cheesecake shot looking north from point 5 (1000 px). Rabid fans will note Sugarloaf Hill on the skyline.
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This is a great time to visit, but do watch for the newly sprouting poison oak.

Bike trails, right wrong and ambiguous

15 February 2016

One day a year ago, as I set out to investigate the old Crusher Quarry, I was standing off the fire trail looking at something when a rattling sound came from up the hill. Two mountain bikers burst out of the woods in a spray of dust and gravel and jerked to a halt nearby, rear wheels tipping off the ground. “That was intense!” I heard one say. Then they rode a few yards down the fire trail to Mountain Boulevard, where someone in a pickup had just arrived to meet them, and a minute later they were gone, with no one the wiser except for me.

Where they’d come from, tracks ran up a delta of dirt to a narrow trail.

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It was really steep, and slippery too (that was a dry winter, you’ll recall). A false move might get a rider impaled on young acacia stumps. And if another biker had hurtled down upon me I had precious little space to duck. I climbed the trail a bit nervously. None of us really belonged there.

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Bikers get an intense ride here. An intense ride is a legitimate thing. But isn’t all they see here just a blur of trees during their minute of white knuckles? What I saw was untreated erosion on the ground, an unpermitted trail in the city’s Leona Heights Park, and a community of scofflaws for whom it’s their personal secret.

After a while I struck off the trail to continue my own intense hike, and that was that. Then the other week I found the trail’s top end, near the Merritt College parking lots.

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The trail is pretty nice up there. Not exactly legal, but not in the city park either. Useful. I even approve of it. I saw access to some nice countryside with splendid views, a well-built trail that suits the slope, and a community of avid cyclists for whom it’s their personal secret.

Once again I got sidetracked, so I haven’t traveled the whole trail yet. Clearly, though, the top and bottom segments, Jekyll and Hyde, meet at the fire road in Leona Heights Park. It would be really nice if the lower part were converted to foot traffic only, with erosion control and occasional steps. Mountain bikers could take the fire road down to McDonell Avenue.

At Leona Canyon Open Space Preserve, less than a mile south, “the park is an ideal place for hiking, running, biking, dog walking, and similar activities.” The intense, pellmell riding experience can be had on either the Artemisia or Pyrite trails there — just not the thrill of living outside the law.


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