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.
6 August 2013
Foothill Boulevard descends to Lake Merritt in this gentle slope down from the old marine terrace (Clinton terrace).
For a mile and half east from here, Foothill runs along the terrace. East of 14th Avenue, where it’s a two-way street, it skirts the steep edge of the Fan at San Antonio hill where the contrast between the two geologic units is most dramatic.
26 July 2013
Way down in the Sheffield Village neighborhood is a big hill and a little hill, but most of the place is in a flat little basin. The geologic map shows it as a patch of old alluvial sediment of the same vintage as the Fan:
The big hill is on the east side, across the Hayward fault (the black line from the lower right corner). The little hill is on the west side, butting against I-580. The road on its west side is Middleton Street, so I give the hill that name. I didn’t realize it when I poked around there earlier this month, but the hill is mapped as San Leandro Gabbro, of Jurassic age. The rock doesn’t show itself very much, but here’s a small exposure. Next time I’ll bring a hammer.
The highlight of the hill is the little private park inside the ring of houses there, just a microscopic piece of the original oak meadow (although this is actually a cork oak).
From there you get a nice view of the big hill. The fault runs along the foot of the hills, behind the homes in the center and in front of the lower set of homes on the right.
Click the photo for a big version.
15 July 2013
My place lies at the edge of the Fan, downhill from the Piedmont block, and the soil keeps producing these gorgeous pieces of lightly polished high-grade chert. I decided that this one should sit for a formal portrait. Click the image for a larger version.
It’s really more of a jasper than a chert. Jasper is a glassier, more refined chert that gets its appearance from the redistribution of silica fluids. This one mixes the red of oxidized iron with the green of reduced iron—at least that is my inexpert explanation—reflecting the invasion of oxidizing fluids at some point during its rough-and-tumble history as part of the Franciscan complex.
I believe that upstream, in Moraga Canyon, there were chert quarries in the earliest days, but I need to check the records to be sure one way or the other. This is not a quarried stone, though, because it has the burnished surface of an object that has been carried a short distance by streams and natural mass movements. I can’t look at it enough.
12 July 2013
I think it’s safe to say that everyone in town is thrilled with the improvements to Lake Merritt. After seeing the final configuration today, I’m feeling a deep satisfaction.
The new roadway and pedestrian bridge over the lake’s outlet serves vehicular traffic as well as ever, but residents and, most of all, the lake and the land get their due. The lake—actually it’s a tidal marsh—is noticeably healthier now that the tidal flow from the bay is no longer regulated with a dam. The range of the tide is greater now and the water is flushed more thoroughly. We have figured out how to trust nature with our lake. We’ll see in the future how the new lake deals with drought and flood, but I think that the city will not overreact to the occasional inundation as it might have in the past.
The new lake is a triumph for the planners of Measure DD, where the money came from. The funds are still being spent on this and many other projects around Oakland, but I’m starting to wonder what the DD crew could do for an encore. Nature holds us in its hand with the Hayward fault, too. Can we envision better ways to live with it?