Archive for July, 2012

Bella Vista hill

22 July 2012

Bella Vista hill is part of the big Pleistocene alluvial fan that sprawls across the middle of Oakland, as shown by the “Qpaf” code on the geologic map.

pleistocene fan

The “Qmt” code is the marine terrace I’ve discussed before. The fan is dissected by modern streams into several lobes, which take their position in today’s cityscape as distinct topographic hills as seen in Google Maps topography:

topography

Bella Vista hill lies in the polygon defined by Park Boulevard, East 34th Street, MacArthur Boulevard, 14th Avenue, East 18th Street and 8th Avenue. All of those street run in valleys or saddles, except that East 18th is on a break in slope. The numbers refer to the following photos, taken from across or in the valley of 14th Avenue Creek.

The hill is low on its bayward side, as shown here from E. 22nd Street.

It has a corrugated surface, such that 9th, 10th and 12th Avenues run on high ground and 8th, 11th and 13th run up declivities. Higher up on the hill, the ground is steeper and the allee of palms marking the former Francis Smith estate is the defining feature of the hill.

The top of the hill has two eminences. The more dramatic one is on the south where Highland Hospital frowns down upon the stream valley.

hospital

Hospitals, like schools, were traditionally sited to take advantage of fresh air. Highland Hospital took its very name from this practice. Here’s a view of the whole hospital complex on the southern boss of the hill.

highland hospital

The northern knob is higher, exceeding 200 feet elevation. At its high end, 10th Avenue becomes Bella Vista Avenue and curves across this peak. Old palm trees from the Smith estate mark it from a distance.

Borax Smith knew what he was doing when he picked this hilltop for his home base. The hills on the fan to the south are a bit higher, but the views to every other direction were unimpaired from that spot. If you want to walk the crest of this hill, go up 10th or 12th Avenue and jog across to 13th and take it all the way up to the I-580 overcrossing.

Knocker 10

11 July 2012

Mountain View Cemetery has been clearing its upper reaches aggressively this year—so much so that a new knocker came into my ken the other week. This view is looking down at it from the brow of the maintenance area, sheltered by a clump of trees.

knocker 10

It appears to be the usual sandstone, although I didn’t inspect it closely. There is a good deal of poison oak around it, as there is near its neighbor, the “high knocker“:

knocker

Knocker 10 overlooks the new Golden Lotus Mountain section.

If you haven’t been up to the top of the cemetery lately, the view east is phenomenal with the eucalyptus trees gone.

Collecting the Orinda

4 July 2012

Lately I’ve been putting together a rock collection for the Chabot Space & Science Center. The last rock I needed was conglomerate, and I slapped my head and said “Duh! Use the Orinda Formation.” So it came to pass that I was on the Gudde Ridge roadcut, east of the Caldecott Tunnel, admiring that distinctive body of rock. But its exposures were off limits due to the construction.

orinda formation

There were two problems. Finding exposures of the conglomerate was difficult. And once I got close to the rock itself . . .

conglomerate

. . . this magnificent stone turned out to be rotten. You may think of conglomerate as a rugged rock, with all that grit and gravel in it. Indeed it can be. But the young, minimally processed conglomerate of the Orinda Formation doesn’t hold up to sun and weather very well. The pebbles work loose and the matrix turns crumbly in a matter of decades. The stuff in that impressive set of stairstep cuts is actually ready to give way, thudding dull under the hammer and totally useless for my purpose.

In connection with the Caldecott Tunnel work, the Fish Ranch Road offramp looks like it may have some fresh exposures. But it’s fenced off.

orinda formation

In the end, I had to find my conglomerate elsewhere. The fresh stone is beautiful, though, and being able to finish the collection made my day.

orinda formation specimen


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