Archive for April, 2008

North knocker, Mountain View Cemetery

30 April 2008

knocker

Continuing my inventory of the knockers of Mountain View, this is on the far north end of the cemetery, along the lowest of the three roads back there. It appears to be the coarse, tough sandstone—technically a metagraywacke—that makes up the majority of the Piedmont block. I can’t always tell what a rock is at the cemetery because I can’t whack it with my hammer. Don’t you try that either.

Managing the lake

25 April 2008

lake merritt

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.

A fault runs through it: Montclair

22 April 2008

montclair sag pond

The Hayward fault runs through the heart of Montclair, in the Oakland hills behind Piedmont. Montclair Park’s duck pond was constructed where the fault left a natural sag in the ground.

Only in seismologists’ equations, and perhaps deep down in the crust, are faults smooth, flat planes. In the world, on the surface, faults are as ragged and variable as any other geological feature. The Hayward fault is more of a zone, from a few to a hundred meters in width, with several fractures running through it. Where two strands overlap, a block of ground between them may slump in tension or rise in compression, depending on how the strands are oriented. At Montclair Park, two strands are mapped on either side of the sag basin. Lake Temescal is another example of a sag basin repurposed as a water feature. So, apparently, is Lake Aliso, the pond on the grounds of Mills College.

The first “great San Francisco earthquake” occurred 21 October 1868 on the Hayward fault. The epicenter appears to have been in southern San Leandro, and surface rupture extended from there all the way down to Fremont. In Montclair, the other direction along the fault, there was plenty of shaking of course, but no rupture of the ground from what we can tell. A trenching study, conducted along the third-base line of the little ballfield in Montclair Park, found no sign of recent movement along the fault there. But slow, silent motion does affect the fault in Montclair. The old fire station on Moraga Avenue has been rendered useless by aseismic creep, and some of the houses along the fault appear to show foundation disruption. But generally creep is invisible unless there is some structure that it affects, like the south curb of Medau Place, below. South of here, the fault crosses Route 13, reaching the other side at the head of Dimond Canyon.

hayward fault montclair

The high knocker, Mountain View Cemetery

20 April 2008

knocker

This knocker can be hard to find. It’s two roads up from Millionaires’ Row and to the south, but its bay-facing side is obscured by trees. I took this photo in 2003; today I could barely see it from the road, and I knew where to look. It’s mostly chert. I’m calling it the high knocker because it’s the tallest one in the cemetery; at least two others are higher on the hill.

If you approach this rock, beware of poison oak.

Knocker on display

17 April 2008

knocker

Mountain View Cemetery is a manicured showcase of the lower Oakland Hills. When Frederick Law Olmsted designed it he left the natural contours of the land, and to this day it’s the nearest thing to the original oak-dotted grasslands that the first visitors saw (although the abundant elk and grizzlies are long gone). And decades before the rock worshippers of the Gilded Age put their stamp on Berkeley’s hill neighborhoods, Mountain View left the knockers alone. There are outcrops of the wild variety up near the utility yard, a couple of chert boulders in charming neglect, and there is this splendid thing left in the middle of its own circle above the Henry Cogswell monument. I should put up shots of the rest of the cemetery’s knockers—I think I have them all.

Basalt masonry

15 April 2008

basalt

I took a walk this morning among my local steep hills. Near the Rose Garden, I spotted a resident clearing his front yard, which was full of Oakland-quarried boulders. He had dug out all the old junipers and was making terraces with the rocks. I told him they’re special now that Oakland has no working quarries. He said he’s trying to get his neighbors to tear out their junipers too—all the houses have these rocks, probably dating from the twenties when they were built. Then I crossed the Chetwood bridge into Adams Point and inspected a bunch of yards of the same vintage, where the same landscaping rocks were common. My guess is that the Leona quarry was the source. I still know little about the Hiller Highlands quarry, but the rock there is different. There are piles of old quarry rock in the slopes below Merritt College that match some of the stones I saw.

But after crossing to the Auto Row neighborhood via the Perkins and Frisbie stairways, I passed this exceptional house along Richmond Boulevard. The stone fence is noteworthy with its jagged top. I shot this picture in 2006; right now it’s covered in vines. And the porch behind it is a splendid example of stonemasonry. It’s all made of basalt stones, and I’m guessing that the rock came from the Round Top quarry (or conceivably the Rockridge Shopping Center quarry). But some time I need to visit the History Room at the main library and find out just what the local quarries produced and when they were active.

Firm clay

13 April 2008

clay

On two occasions I’ve spotted construction sites on the fringes of Haddon Hill, once at the corner of MacArthur Boulevard and Wesley Avenue and once at the west end of Brookwood Road. I asked what the ground was, and both times the owners said the same thing: “firm clay.” There is no bedrock to speak of west of the Hayward fault, outside the Piedmont block and Toler Heights, up where 98th Avenue ends. It is safe to say that any Oakland neighborhood named “Heights” or “Highlands” has some bedrock under it, and some of the “-monts” do. But the rest of the hilly places that adjoin the flats are firm clay, with maybe a little sand and gravel. If the slope isn’t too steep, this soil is good for building.

All are part of a large alluvial fan dating from late Pleistocene times. It stretches from Pill Hill to Evergreen Cemetery, and its closest approach to the Bay is here at San Antonio Park, overlooking Coast Guard Island.

san antonio

Its sediments are said to contain “extinct late Pleistocene vertebrate fossils.” I haven’t read the literature, but that could mean anything from Ice Age mice to the mammoths, horses, camels, sloths and bison known from other Bay area sites, not to mention some extinct great cats. It’s worth keeping an eye on this stuff.


Follow

Get every new post delivered to your Inbox.

Join 3,954 other followers