25 September 2013
Elverton Drive is a very distinctive place in the high hills, not so much for its houses—though no insult meant to their owners—as for its bedrock. From end to end, it offers the best exposures anywhere of the Claremont chert.
If it weren’t for the parking situation, this would be a great spot for a class exercise in field mapping. The strata are clear, the winding road offers a range of orientations to refine measurements, and the rock isn’t totally uncomplicated. Take this spot.
What is the nature of the change between neat rows and rumpled layers? What can the student conclude from the evidence, and what should the student look for elsewhere to test those conclusions? I don’t know; I’m just asking and I didn’t inspect this closely. Besides, it might be on someone’s homework.
A few years ago, Elverton was blocked by a landslide. Residents could get in and out from either end, so it wasn’t that bad, but I stayed away until a few weeks ago. I think that this spot must be where it was. (If it’s not obvious, this is sculpted concrete.)
Near the road’s east end is an old excavation, perhaps a small quarry, where you could examine these rocks at leisure and collect a specimen. But do notice the presence of fallen blocks, and if you feel an earthquake while you’re there, step the hell back.
East of Elverton, the chert crosses the ridgeline into the Huckleberry Preserve and trails into the back hills.
16 September 2013
This caught my eye by the side of Merriewood Road: an artifact of the early infrastructure in the Oakland hills.
It wasn’t until I checked just now that I realized how old this must be: The People’s Water Company was founded in 1906 and went bankrupt eight years later. At this time Oakland and the East Bay were seriously hampered by the limits of the local water supply, but somehow they ran pipes up here and got water to them, for a while.
Seems like a museum should have this. But the Oakland Museum of California is not a museum of Oakland, and the Camron-Stanford House, which started out as the city museum, is just a Victorian costume home. Who collects historic artifacts for the city of Oakland?
8 September 2013
A comment to one of my posts talked about the sulfur springs of Bushy Dell Creek, in Piedmont Park. I said I couldn’t detect any and the commenter said where to look. So a few weeks ago I looked and found this small example.
It’s just a trickle, but it offers a whiff of sulfur gas. More tellingly, it supports gray filaments of sulfur bacteria, seen here in closeup.
These look like pollution, and I guess in our context that’s what they are. But whole microbial ecosystems center on a molecular economy of sulfur, oxygen, carbon and hydrogen. They’re mostly hidden underground near sulfur-bearing minerals, but here and there they get flushed out into the light.
1 September 2013
Lakeside Park is one of the most parklike parks I know. Perhaps I feel this way because I imprinted on it at kindergarten age.
Youthful feelings aside, I think that geology makes the park this way: it’s set on the late Pleistocene marine terrace, planed and beveled by the sea waves during an interglacial highstand approximately 125,000 years ago. The planar setting, studded with trees to the limits of vision, suggests a vision of infinity, or at least limitlessness.
This spot is in front of Children’s Fairyland, where young children then and now can experience mind-blowing things everywhere they look. Show them these rocks, too: they’re ochre-stone and chert from our own hills.
23 August 2013
Years ago, a homeowner installed this yard facing Humboldt Avenue. I think of it as a California zen garden.
These days, landscapers are obliged to buy rocks that come from out of town, produced in anonymous quarries by the big-rig load. This yard could have been furnished with stone from just a couple miles away. One of my many pipe-dreams is to set up a stoneyard where I’d salvage and sell recycled rock from local sources. The market would be vanishingly small, but if just a few people cared that might be enough.
19 August 2013
Piedmont’s Witter Field occupies the valley of Bushy Dell Creek, in an opening in the topography where a large formal garden once sat. The creek is culverted here, but once in a while it needs attention, as it did last month. Out of sight is not out of trouble.
It reminds me of the city streets: it seems like as soon as a nice new pavement is put down, a crew comes along to cut it open, as if the asphalt were there just to make a clean work surface.
11 August 2013
A few weeks ago I managed to get a very nice view of the roadcut where the end of Gudde Ridge was trimmed to make room for route 24, east of the Caldecott Tunnel.
That’s the lava flows of the Moraga Formation on the left. On the right edge is the coarse conglomerate of the underlying Orinda Formation. Click the photo for a 1000-pixel version. (The cut on the north side of 24 is shown here.)
This is not a view straight on; the ridge runs toward the lower right, so the steeply tilted rocks look vertical from this angle. It can often be hard to figure out the exact orientation of rocks, even in a splendid exposure like this.