Archive for the ‘oakland geology puzzles’ Category

The hunt for Rockridge Rock

3 July 2008

The Rockridge neighborhood has migrated over the years. Today Rockridge centers around the Rockridge BART station, in the valley of Temescal Creek. But a hundred years ago, Rock Ridge referred to the highlands between that valley and the one to the southeast, through which the Rockridge branch of Temescal Creek flows (in the Claremont Country Club golf course and upstream along Broadway Terrace). The ridge was supposedly named by the Livermores, who put their mansion on it amid their 600 acres of land making up today’s Upper Rockridge neighborhood.

There was a famous rock somewhere up there that became a popular picnic site in the late 1800s. Photos show it as being blocky, massive stone, maybe 10 meters in height and greater in width, big enough for dozens of people to stand on for their portrait. Lately I’ve been trying to find it. Old maps don’t show it, but Jonathan Chester’s excellent book Berkeley Rocks has some information. He claims that the developers of the area named the rock itself Rock Ridge and encouraged the public to visit it. Today I found an article from the Call of March 12, 1910 about the area:

“Hundreds of people went out to Rock Ridge park, during the week, to enjoy the inspiration found in the budding trees and flowers awakened by the first touch of spring. The visitors found that the opening of streets, avenues, walks and drives through the famous old Rock Ridge picnic grounds has facilitated access to the points of interest. Those who have known best and enjoyed most the peculiar charm of the place were delighted to find that the plans of the owners of the Rock Ridge property in laying out the tract with wide streets and avenues and ample lots have preserved the distinguishing features unimpaired. The army of admirers of Rock Ridge property has received new recruits every day. A number of sales of lots, were made during the week to people who will build immediately fine homes on their grounds. The street work is being rushed. The planting of flowers and shrubs along the cement curb line is also receiving attention from a force of [men].”

The story suggests that while the “famous old” picnic grounds were wiped out by subdivision, “the plans of the owners . . . preserved the distinguishing features.” From this evidence and that cited by Chester, the rock was widely known and hard to miss. Therefore I can’t understand why Chester thinks that the site of the rock is on Glenbrook Drive at the corner of Bowling Drive:

rockridge rock

It’s a beautiful outcrop, nicely integrated into the two properties that own it, but no way is that the Rock of Rockridge. It’s the wrong size, the wrong shape and the wrong rock type. And the Call story at least hints that the Rock was “unimpaired” as of 1910.

I think that Chester may not have looked hard enough. I have found at least two other candidates for the Rock, but there is still some ground to cover and many places for rocks, even huge ones, to hide.

The Old Tunnel (one of them)

3 May 2008

tunnel

The former car tunnel through the Oakland hills had its entrance (or its exit, whichever you prefer) here at the top of Tunnel Road. The road is very popular with bicyclists now, and in the five years since I took these photos new houses have been built and things cleaned up in general.

tunnel

At the little space in the intersection where the fare gates must have been is this pedestal and plaque. Would love to hear some of the history of this.

tunnel

And, of course, the rocks. Here we have the Claremont Chert so typical of the northern Oakland hills. I need to visit here again soon, although it’s probably less accessible now.

The other old tunnel is at the top of Shepherd Canyon, where the train used to go.

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.

Montgomery Ridge

16 March 2008

bowlofchert.jpg

St. Mary’s Cemetery, north of Mountain View Cemetery, is on a ridge that runs toward the bay and peters out at the Kaiser hospital on Macarthur and Broadway. The ridge is on bedrock at the high end and changes to old alluvial fan sediment just past Pleasant Valley Boulevard. I call it Montgomery Ridge because Montgomery Street runs approximately up its crest. My yard lies on the edge of this ridge down near its end. I find these Franciscan chert cobbles scattered thinly in the dirt, and I’ve been putting them aside. They are rough, but not jagged, so I take them to be natural, in-situ alluvium rather than fill or crushed rock. That’s where things stood until the other week, when I found a cutbank on upper Howe Street dug into the ridge, and the same chert was tumbling out of the hillside from a layer just beneath the topsoil. Walking down Montgomery, I saw more chert chunks in the soil by the road at the corner of John Street. My favorite pieces are the greenish ones, like this one by the side of upper Howe Street.

howegreenchert.jpg

This chert comes from the Piedmont block, but the geography is different today. Today, streams have incised the old fan and they’re too feeble to carry this kind of material. I picture much drier conditions, and flash floods strewing the chert across the surface of the ancient fan. The next thing is to see where else it occurs. Let me know if you find it in your neighborhood.

Sausal Creek in flood

4 January 2008

dimondflood.jpg

With the heaviest rains I’ve seen in years, I checked out Dimond Canyon today to assess the power of the stream in it, Sausal Creek. The water was brown and impressive. It looked about waist-deep at most. I don’t know how this stream cut the canyon, which is a gorge more than 50 meters deep with stone walls. But I have a theory involving stream capture and movement on the Hayward fault, just upstream from the gorge. At various times, the fault has pulled the canyon past different watersheds. Perhaps lakes lay upstream, or landslides formed dams, that collected enough water to give the canyon a good downcutting once in a while. I hypothesize that the stream’s watershed was once quite a bit larger, perhaps even the valley now occupied by Chabot Reservoir. But the timing has to work.

There are at least two other gorges in the Oakland foothills that appear oversized to me: the upper reaches of Cemetery Creek, along Moraga Road, and the canyon of Peralta Creek in Redwood Heights, best seen from Rettig Avenue north of 35th Avenue.

It is recorded that the early loggers who stripped the redwoods out of the Oakland hills used to float their logs down Sausal Creek to the bay. All I can say is, there must have been a lot more water in the hills back in the 1850s, because even today’s deluge couldn’t have done that.

BTW see the Friends of Sausal Creek site.


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