Archive for the ‘oakland geology views’ Category

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.

walk30topo

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.

trestlepowerline

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.

walavistavalley

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.

great valley

And here’s a closeup from nearby.

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

Fault valley

21 October 2012

October 21, not October 17, is Oakland’s real Earthquake Day. While many of us remember the 17th vividly, the day of the Loma Prieta quake in 1989, the morning of October 21, 1868 was when the original Great San Francisco Earthquake struck. It was on this side of the bay, on our own earthquake fault, and the ground cracked from Fremont all the way to the edge of this view from the end of Pali Court, in the neighborhood just across route 24 from Lake Temescal.

hayward fault valley

The Hayward fault runs from the notch on the skyline, which is in Montclair, to the right edge behind the house in the middle distance. This part of the fault, between Mills College and Lake Temescal, is the only place that has large areas of bedrock on both sides. What that means for the purposes of today’s post is that it’s the most rugged and picturesque part of the fault and has probably the greatest concentration of million-dollar homes.

Today I invite you to review this blog’s category “the hayward fault.” I seem to have rattled on at great length on this subject. Some day the fault will rattle all of us at great length.

Today’s Oakland Tribune has an article about newly mapped faults in the Hayward fault zone; I won’t link to it because the Trib’s links die quickly. But the new Alquist-Priolo zone map can be accessed here.

Calmar, Mandana, Longridge

7 October 2012

I’ve been exploring the surprisingly intricate topography between Lakeshore Avenue and Park Boulevard, where I count four separate ridges separated by three valleys. From the ground, it’s a challenge to visualize and photograph. This is the view across Mandana valley from the side of Calmar ridge, on Santa Ray Avenue, to Longridge.

longridge

I haven’t forgotten the blog, I’m just real busy. The weather lately has been superb for walking.

Linear scarps

1 September 2012

Next Saturday, 8 September, I’ll be leading a short, rugged urban walk for Oakland Urban Paths that among other things will visit these faceted spurs along the Hayward fault. Seen from the north . . .

view south

and from the south:

view north

The downhill side is moving north with respect to the near side. The open land in the foreground is the King Estates Open Space.

This will not be a stairway walk. The off-street passages are steep, weedy dirt paths that have not been maintained. The land along the fault is steep, making for nice residential view lots. I haven’t finished the route yet but it will take no more than 90 minutes, 10 to 11:30—I have a lunch destination I’m anxious to make. So I would like to set a good geologist’s pace. Details and questions as they come to you over at Oakland Urban Paths.


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