26 October 2013
I enjoy seeing some of Oakland’s more unusual rock types when they show up in people’s yards. It shows that people like our rocks.
This boulder of actinolite may not actually have come from Oakland, but it could have. Perhaps a resident spotted it in a streambed and said, “I give this to me.” It’s clearly not part of a professionally assembled landscape package.
19 October 2013
This house on Melvin Court has a splendid front yard based on serpentinite: serpentinized peridotite on the right, a serpentine-lined walkway with slate in matching colors, and inlays on the path composed of serpentine medallions. The house itself is painted serpentine blue-green. Click the photo for a big version.
The Oakmore district is uniformly mapped as Franciscan sandstone, but just a little farther east it’s mapped as undivided Franciscan, so we might expect a mixture of possibilities here. The neat lines on the geologic map are as much hypotheses as they are conclusions. Other outcrops nearby look like volcaniclastic rocks, and some of this home’s neighbors use it effectively. I conclude, though, that this home’s landscape was composed with imported stones rather than assembled from what was lying around. But the rocks may well be Oakland natives from just up the way, perhaps even from the Serpentine Prairie quarry.
6 October 2013
Out in East Oakland at the corner of 85th Avenue and Baldwin Street is this fine, underappreciated boulder.
To all appearances, it’s good old Oakland chert, hard at work. I assume it was put here to keep vehicles from cutting across the corner, or perhaps to keep a runaway vehicle out of the building behind it. Who knows? I was just glad it was there to break the monotony. It’s free of graffiti, too.
The other end of Baldwin Street is east of the Coliseum, where it serves as a back entrance for staff and athletes, at the edge of Arroyo Viejo. That’s the creek you cross when you’re walking from the BART station to the game. So between stone and water, Baldwin Street pays more homage to geology than most of its peers.
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.