Archive for the ‘oakland geology views’ Category

Leona Canyon

23 April 2013

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Leona Canyon Regional Open Space Reserve is an East Bay Regional Parks District property of some 290 acres that is entirely within the Oakland city boundary. It’s got rocks.

The canyon was cut by Rifle Range Branch, part of the Arroyo Viejo stream network. The branch joins Arroyo Viejo underneath I-580 at the turnoff to the zoo. The topography is rugged. I surmise that the rifle range that gave its name to the creek was here once upon a time, because it’s the sort of place where you could shoot a lot without disturbing the rest of the city.

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Here’s the geology of the same piece of ground.

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The pink “Jsv” is the same metavolcanic rock (Leona “rhyolite”) found in the Leona Quarry just to the west. The green units are the familiar sedimentary rocks of the Great Valley Sequence, tilted upward so that they get younger to the east. The units, in order of age, are the Knoxville Formation (KJk), the Joaquin Miller Formation (Kjm), the Oakland Conglomerate (Ko) and the Shephard Creek Formation (Ksc). You can see that the canyon is controlled by the faulted contact between pink and green.

OK! The creek is dammed at the base of the canyon, presumably just for flood or sediment control. Maybe the rifle range used to be here. Anyway, the creek is fairly level throughout the park, creating a nice bit of habitat.

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As you walk up the creek, it wanders along the contact between the two major rock units, so you’ll see a mixture of boulders in the creek bed. The Knoxville is a shale with some sandstone, not very distinguished, but near its base it includes some conglomerate and breccia: rocks made of pebbles and cobbles derived from the Leona keratophyre. This example is from the high end of the trail, in the upper left corner of the geologic map.

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The reserve has two paths that lead up the canyon’s sides. The Pyrite Trail goes west through the metavolcanics. It’s shady and steep. I should note that I saw no signs of pyrite on it.

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Along this trail you’ll see the Leona metavolcanics, kinda ragged-looking stuff that’s been chewed up and spit out a few times since it was a volcanic island arc during the Late Jurassic.

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There are nice views of the other side of the canyon, which is more open and chaparral-y.

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The trail up that side is called the Artemisia Trail. I’m not sure that either trail’s name means much. It passes a lot of this fine-grained sandstone.

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Higher up, you get a good look at this big knob, which is a prominent part of the hills’ skyline as seen from the north. This view is from the south.

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There seem to be a few informal trails on it, and the view must be fantastic. But the Artemisia Trail offers superb views across the middle and south bay, too. I’ll be back.

West Oakland topography

10 March 2013

West Oakland has always been flat and easy to build on, whether it was for factories like the old Shredded Wheat plant built in 1915 (still operating as California Cereal Products) . . .

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or for the middle-class Victorian homes that are West Oakland’s pride. It takes a lot of walking around to note the subtleties of the landscape. Except around Raimondi Park, the area was never a coastal marsh but was slightly elevated sand dunes, the same Merritt Sand that underlies downtown. In the Ralph Bunche neighborhood, north of 18th Street between Market and Adeline, the homes perch above the street, not by much but consistently.

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Even century-old homes sit up the same way as the newest places. Presumably the streets were dug down, but maybe the lots were piled up too. Perhaps flooding was a concern, and all the earth-moving created more desirable lots here. Only a historian with intimate local knowledge could say.

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If you look north along any of these streets (Chestnut, Linden, Filbert, Myrtle), you’ll see the land sink at Grand Avenue where the Merritt Sand leaves off.

Dimond valley

6 February 2013

Sausal Creek is responsible for digging a floodplain that is rather wide just upstream from I-580. Here’s the view across it from Montana Street at MacArthur.

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The squat tower just to the left of the speed limit sign is at the foot of Lincoln Avenue, and it’s at the same elevation as where I’m standing. That’s how wide the valley is. Here’s another view looking right down MacArthur.

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The first cross street is Canon Avenue, the next one is Dimond Avenue leading up to the park, and beyond is the Fruitvale Avenue crossing. Here’s how the geology is mapped.

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You can see that the stream valley is wide because three streams coalesce here at the edge of the Piedmont bedrock block. Restricted upstream, they enter the big alluvial fan (Qpaf) and have room to move and easy material to erode. It is curious that Sausal Creek hugs the west side of the valley; I suspect that tectonic movements may account for that, but only a decade or so of careful satellite altitude monitoring can answer my suspicion.

Northern Upper Rockridge walk (#30)

27 January 2013

Walk number 30 in Charles Fleming’s Secret Stairs East Bay, which he refers to as upper Rockridge west, goes from the Rockridge BART station over the Franciscan bedrock hills of upper Rockridge. The views are great, and there are a few rocks as well.

Here’s the route map (click it for a larger version).

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And here’s the route shown on the geologic map. It goes counterclockwise.

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The orange Qpaf is old alluvial terrace, KJfm is Franciscan melange, and fg is Franciscan greenstone (you might see a little of that near the end if you’re vigilant). Melange is lumpy stuff, as I’ve said before, mostly shale with knockers of harder rocks here and there.

And here’s the topography, with the sites of the following photos marked on it. The walk basically circles the bowl cradling little Rockridge Park with a couple of forays over its rim.

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The new parklet at the BART station is nice. Naturally the boulders were sourced elsewhere.

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The first part of the walk is housewatching until you cross Broadway to Rockridge Boulevard, where you face the hills through an allee of big palms. We’re at the 200-foot contour and looking at homes above 400 feet. It’s steep land, but not as bad as the high hills.

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Once you get up into the hills, you get views in all directions. Pick a good clear day to do this walk.

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As you go along Acacia Avenue, keep an eye out for Cactus Rock, reputed to be The Rock that gave Rockridge its name. I’m not fully sure that’s true, but I’m at a dead end in that quest at the moment.

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The high point of the walk is on Alpine Terrace, at about 450 feet. It has several empty lots left over from the 1991 Hills Fire. This one always gives me a qualm.

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The top of the elaborate Brookside Steps features this gnarly boulder, which I’ve featured here before. This is what they should have used down at the BART station.

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As you wander over to the north end of the loop, enjoy the views that way. Here we have the chaparral of Claremont Canyon, the homes of the Claremont Hills neighborhood, and in front the solar roof of the College Prep School, which I was pleased to see produced a finalist in the Intel Science Talent Search this year. That is a huge brag for Oakland.

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Here’s a view of upper Hiller Highlands, including one of the two big round houses up there. This is the lower one, at the end of Devon Court.

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And here’s the view east toward the eastern, higher crest of upper Rockridge studded with homes. A glimpse of uppermost Broadway Terrace is at left. All the distant points in these last three photos are across the Hayward fault.

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The long, sturdy stairway was constructed by Schnoor & Son. By my reckoning, that makes this 100 years old. Other sidewalk stamps up here date from 1913.

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We’re finally going back down in to the bowl of Rockridge Boulevard, so you can see now what those high homes have for views—straight out the Golden Gate. The good burghers who settled this area a century ago would take these steps to catch the streetcar to their jobs across the bay.

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Here’s the view of Claremont Canyon from Broadway and Keith. The white bit by the traffic light is the tower of the Claremont Resort. The nearer ridge is just in Berkeley across the valley of Temescal Creek.

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And from here it’s a straight walk down to the refreshments of College Avenue. There are bits of bedrock along the upper part of Keith, but then you’re back to the lowlands.

Oakland powerlines

7 January 2013

Oakland’s infrastructure includes two major powerlines across the hills. One starts from the 1922-vintage substation on Landvale Road (the Claremont Substation) and runs parallel to route 24. The other starts from the vintage substation at Park Boulevard and Grosvenor Place (Substation X) and runs up Indian Gulch, Dimond Canyon and Shepard Canyon. Both of them offer little islands of open land, secret parks, around the support structures.

This idyllic spot, photographed in November, overlooks Indian Gulch between Hollywood Avenue and Glendome Circle.

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And here’s a view of the Claremont Substation and powerline just east of Lake Temescal, taken in October 2008. This bit of empty land can be reached from the top of Pali Court or by a scramble up from Broadway or another scramble down from the fire road past Swainland Reservoir.

claremontsubstation

Like geologists, powerline operators have a totally different view of the city than most people. I’m a little surprised there aren’t more powerlines here, but two is plenty. (A third, smaller one runs through Oakland lands up Strawberry Canyon from the Cal campus past Grizzly Peak.)

Walavista valley, 1916/1925

25 December 2012

I have found a new time sink at the Online Archive of California, where this photo of undeveloped Walavista Avenue, from 1916, is posted as part of this collection.

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The camera is on top of Warfield ridge, west of Lakeshore, just uphill from Fairbanks Avenue. The wooded gulch at back left is the charming little valley that Portal Avenue runs up, right at the Piedmont line. The Alameda Quarry, where Davies Tennis Stadium now sits, was just to its left, discreetly out of this developer’s portfolio photo.

Here’s roughly the same view in 1925. The view from there is still nice, but much more obstructed today.

walavista-1925

The street on the left is Arimo Avenue, running up the smallest of the ridges south of Lakeshore, and the ridge on the right is populated today by Balfour and Calmar avenues. It is fascinating to see this topography in its original form.

Tunnel approach

31 October 2012

I’ll be taking a tour of the new Caldecott Tunnel bore on Friday. This is the view of Route 24 from the ridge south of it, across from Hiller Highlands. Everything here is east of the Hayward fault.

great valley

On the right is uppermost Broadway, where a line of locals and advanced commuters chronically hope for a few seconds’ advantage by merging at the last second before the tunnel. I’ve decided that it’s faster to get in the left lane of 24 as soon as possible and stay there. Anyway, all the land from here to the far curve is underlain by rocks of the Great Valley Complex, of Late Cretaceous age. A fault separates it from the Sobrante Formation behind it, which is much younger. The lower part of the skyline ridge is Sobrante, but the high part is chert of the Claremont Shale. The tunnel penetrates both of those units, and I hope for a good look at it.

I was standing by the power line; you get to it by hiking down the road from the sports complex, on Broadway at the overcrossing, or by ducking around the gate at the top of Pali Court. The Great Valley here is a mix of fine-grained sedimentary rocks. Exposures are poor and the fabric is disrupted. Here’s an exposure on Pali Court.

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And here’s a closeup from nearby.

It’s very shaly. The lenses of more siliceous stuff don’t add to its strength.


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