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.

Our native forest

8 February 2016

I spent Saturday in Napa Valley on a field trip with the Northern California Geological Society, visiting the ultrapremium Promontory vineyards west of Yountville and the merely superpremium vineyards of Harlan Estate west of Oakville.

High-end wine is a culture obsessed with the character of land, and Bill Harlan talked a lot about his land as we tasted the 2009 releases from both sites. What struck me most was his emphasis on the forest around the vineyards. Both properties are enclaves of vineyards in a forested setting. This view of woods-encircled vines is from the top of Promontory.

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Harlan spoke of airs and influences while, given my recent reading, I thought of wild yeasts and soil microbiomes. I also thought of Oakland’s woods, which have been on my mind lately as I’ve explored the Leona hills.

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To some Oaklanders, all trees are good trees. To me, the oak forest is what belongs here, and eucalypts should be exterminated from our wild lands. I’ll spell out several reasons, mostly familiar, plus a new one about living in Anthropocene time. But first, a clump of oaks in the Leona hills.

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History: Once our oaks were the basis of a thriving native economy, and their acorns are still here in abundance for true locavores. Eucalypts were planted in our hills in a failed attempt to make a killing in timber. The poet Joaquin Miller, spellbound by a Victorian ideal of Arcadia, covered his grassy Hights with thousands more. Neither wave of tree-planting was done responsibly. We owe that legacy of heedlessness the same respect we owe pampas grass, French broom, foxtail grass and other pest species. Here’s a mono-stand near the Caldecott Tunnel.

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Aesthetics: Our native oaks hug the hills in fleecy blankets; eucalypts hide them in scraggly tufts. Compare the two types of forest, side by side at Lake Chabot. The very air is different.

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Accessibility: In my search for rocks, I go off trail and across country. Eucalyptus country is typically impassible, the footing noisy and slippery. Oak country is typically parklike and quiet, like this grove in the Leona hills — although it’s friendlier to poison oak, I’ll give you that.

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Ecology: Oaks make food and mulch; eucalypts make trash.

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The Anthropocene: The future’s climate is up to us. It’s vital that we pull CO2 out of the air. Trees are touted for doing that, but planting and managing forests is a sophisticated practice we’re just beginning to understand. Forests are more than just groves of fixed carbon. By far the majority of a forest’s carbon is in its soil, not above the ground.

A newly published study argues that more than two centuries of reforesting the European landscape hasn’t made a lick of difference to its CO2 balance. Because the new forests were managed for timber, the wrong kind of trees were subsidized.

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Luckily, we don’t harvest timber in Oakland any more, so we can do things the right way. That means nurturing the biomes that suit the region: native oaks, redwood, chapparal and coastal wetland. Their intricate webs of underground organisms, tuned to our rocks and climate over thousands of years, soak up carbon better than any other strategy.

Well-chosen eucalypts are splendid specimen trees, but they should be phased out in the wild. If we feed our wildland soils correctly, Oakland can do its share to fight global warming. And it will be better in all the ways I’ve mentioned.

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Restoring our land will take time, sustained funding and the same dedication that Bill Harlan gives his vineyards. If we take our ownership of Oakland’s land seriously, we can’t slack.


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