Siesta Valley

Last week I took a nine-mile ramble up Claremont Canyon, then along the East Bay Skyline Trail as far as Lomas Cantadas, then down to Orinda and the BART station. The trail goes across the head of Siesta Valley, an interesting geologic feature and a wonderful view (click full size). Route 24 cuts across the valley right in front of the construction, which will be Orinda’s newest neighborhood some day.

This valley is not a streamcut valley, but rather is formed by the folding of the rocks beneath it in a syncline. That’s a shape with a trough in the middle and upturned sides. (The opposite is an anticline, a ridge with downturned sides.) The notch that route 24 goes through is cut by a stream. My guess is that it’s a water gap, cut by the stream at the same time as the rocks were being folded. The rocks of the Siesta Valley are sandstones and mudstones belonging to the Siesta Formation, the next youngest set of rocks after the basalt flows of the Moraga Formation. Speaking of which, I also took this shot of Round Top from the north, with the old basalt quarry grounds in front of it.

Huckleberry

Huckleberry Botanic Regional Preserve is a little-visited piece of wildland just over the Oakland Hills crest south of Sibley Volcanic Regional Preserve. It owes its existence to this rock, the Claremont Chert. The brochure lavishes attention, and rightly so, on the plants of the botanic preserve, but it’s also a good place to see the chert in many settings. Cliffy here or buried there, shaly or rugged, the chert asserts itself amid the soils and growth like the bass player in a jazz combo.

Owing to its history, the Claremont Chert is high in silica and low in nutrients. It drains quickly and breaks down slowly, and for the purposes of today’s vegetation it slows down the natural process of faunal succession—the series of plants that goes from pioneer species to climax forest. Thus where much of the hills is a uniform oak/madrone woodland, the Huckleberry Preserve is a variegated assemblage of everything from gravelly manzanita balds to soft seeps populated with irises, plus huckleberry thickets of course. Hike the nature trail and meet some of the natives. The self-guiding brochure carefully states the role of fire in maintaining the hill ecosystems, mainly to show how the Huckleberry is an exception. But these days, everywhere you look in the hills is a fire long overdue. Some day we will have to catch up with the Ohlone tribes, who managed these lands with regular burnings.

The trail provides several fine views eastward. You can pretend that white settlement never happened and imagine Mount Diablo pristine, as it was when Cabrillo forced his men through this land 250 years ago. (click for larger version) And you can enjoy Round Top’s symmetry from the rare southern vantage:

Heights and flats

In the East Bay, the Hayward fault separates high ground and low, with a few exceptions. Oakland is an exception (so is San Leandro, Berkeley and points north). From Oakland’s southeastern extreme at Lake Chabot up to the Panoramic neighborhood, the fault generally has a few hills on its Bay side. If you ride BART and look up at the hills, the fault is almost entirely hidden. The hill Piedmont sits on is the largest body of rock west of the fault. So Oakland is not like Hayward or Union City, where the fault is quite stark.

But here on upper Dwight Way, at Oakland’s far north end, is a spot where the height/flats dichotomy is laid right out plain. (Click the photo for a 900×750 version.) This little canyon is the one just north of Claremont Canyon, and I don’t know if it has a name. Behind me is little Dwight Canyon and just to its north is Strawberry Canyon, where the Cal stadium sits. High rock hills lie above the fault, and a plain of deep sediment lies below, an area where seismic shaking is liable to cause ground liquefaction. Of course landslides could happen where I stand; the brown patch below looks like a landslide scar . . . pick your poison.

Panoramic Way in (yes) Oakland

Panoramic Way is one amazing street. It starts in Berkeley right at the Cal Stadium, crosses the Hayward fault immediately, and winds upward into the hills past one fine house after another. Then it enters Oakland, forming the spine of the city’s northernmost neighborhood. On a day like today, the view is as good as it is from anywhere in the bay area. Some day I’ll climb Panoramic Way all the way to its top, but today I’m beat.

Bedrock is scarce, but what I saw in one spot looked mighty like the basalt of the Rockridge Shopping Center quarry:

But the area is mapped as Great Valley Complex. Go figure.

The top knocker of Mountain View Cemetery

Up at the very top of the public part of Mountain View Cemetery is this knocker. I think it has a mixture of rock types in it, but I haven’t lain down on it with my magnifier to tease them out. For now let’s call it greenstone, which is how the area is mapped. The stone is a bit dirty, unlike every other knocker in the yard. The groundskeepers ought to give it a good scrubbing with a water jet.

Across the road from here the other week, I passed a pile of rock and soil from a grave excavation and fingered a few of the stones—looked like a gray basalt. Greenstone is a mildly metamorphosed basalt; it often has wiggly veins of carbonate. See three examples starting here. It is somewhere between about 160 and 70 million years old, that is, Jurassic to Cretaceous.

The view of the bay and the city from up here is fantastic. The view of the hills has potential. The cemetery is slowly getting rid of the eucalyptus along the east side, and more and more of the lush hills and neighborhoods is visible every year.

Managing the lake

Lake Merritt needs a lot of care and attention to perform at its top level. This view of the pergola at its east end shows one of at least three aeration fountains in the lake. Without the oxygenation provided by these fountains, the organic matter brought in by the tides and streams, and deposited by the abundant bird population, would periodically overwhelm the natural oxygen dissolved in the water and turn the lake into a stinking anaerobic pond.

Without upkeep, this site would quickly revert to the tidal marshland that it once was. That would be nice in its way, but city-dwellers would probably complain about it. Click the photo for a postcard-type view of this end of the lake taken last weekend.