Manzanita ridge

28 April 2014

The ridge traversed by Manzanita Drive is one of Oakland’s highest residential areas, higher than 1400 feet. It’s the home-studded rise in the Oakland skyline to the right of Round Top in the blog’s banner image. Here’s the topographic view, from Google Maps:

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. . . and here’s the matching part of the geologic map:

manz-ridge-geo

The ridge crest is held up by the Claremont Chert (Tcc), while Skyline Boulevard and Arrowhead Drive, running parallel just to its south, go through the crumbly Sobrante Formation (Tsm). (The other formations are the Orinda Formation, Tor, and the unnamed Eocene sandstone of upper Shepard Canyon, Tes.) Here’s the chert exposed at the west end of Manzanita; it and the next two photos click bigger.

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The views are terrific. Here’s the view north over the Huckleberry saddle to the smaller ridge of Claremont Chert that Elverton Drive skirts.

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The middle of Manzanita offers fine views of Round Top.

Click for 800-pixel version

And the other end of Manzanita, past the unexpected Hills Swim & Tennis Club, is another saddle at the top of Shephard Canyon where the road to Canyon and Moraga crosses the hills.

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More than anywhere else in Oakland, this is an island in the sky.

Arroyo Viejo emerges

13 April 2014

Quietly, at the edge of the Coliseum station parking lot, Arroyo Viejo comes out of hiding from beneath Hegenberger Expressway. It runs under the walkway to the Coliseum and joins Lion Creek just short of the bay.

arroyoviejomouth

Even in its coffinlike culvert, the stream wants to curve, laying a gravelly point bar on its left bank and trying in vain to erode the angle of the culvert’s course into a nice meander. Sorry, old creek.

Local stone

31 March 2014

I always get a kick from old walls around Oakland that are made of local stones. This one is on Loma Vista Avenue, in the upper Laurel.

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Click the image to see a 1000-pixel shot of the whole thing. The mix of blue Franciscan rocks, golden Tertiary sandstones and the occasional reddish chert is distinctive, and it’s nothing that a local landscaping yard would ever offer. Its charm is homely and understated, but authentic.

We haven’t had a working quarry in Oakland for many years, so a lot of these walls are old, or rebuilt. Lovers of local stone today have to scavenge what they can from recycled rocks or their own cellar holes.

Our slides

26 March 2014

A large, deadly landslide in northern Washington has been making news. Smaller ones around here aren’t deadly, thank goodness, but they are sneaky and expensive and everywhere.

slidescarp

This isn’t a landslide yet, but these concentric cracks in Skyline Boulevard are typical signs of slumping ground. A city with more money to maintain streets would have dribbled tar over these cracks when they first appeared, a year or two ago. As it is, each crack lets rainwater into the hillside where it promotes more slumping. Keeping the road sealed will buy a few years’ time.

This location is underlain by the same incompetent Sobrante Formation that gave the Caldecott Tunnel builders such trouble. But landslides occur in Oakland on nearly every geologic unit, from the lower streambanks to the highest hills.

Fruitvale Station vista

24 March 2014

Sometimes the weather is clear enough, but just hazy enough, to reveal the details of the landscape for quite some distance. A week ago the view down the line from the Fruitvale BART station looked like this.

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I know it’s a small image, so click on it for an annotated 1000-pixel version. Most of the view extends beyond Oakland city limits. The farthest peaks are in the Ohlone Wilderness east of San Jose, some 30 miles away. Once you become familiar with our skyline, it’s never boring.

The Easton & Wilson Quarry

6 March 2014

The Head-Royce School occupies a lovely secluded site next to Lincoln Avenue. Naturally, it was once a quarry.

headroycequarry1

Not just any quarry, although its product was ordinary: crushed rock of indifferent quality. It was the quarry for Easton & Wilson, a paving and construction company founded in the late 1890s by Kimball G. Easton and Arthur R. Wilson. (Wilson also partnered with Easton’s brother Stanley in the Leona Heights Quarry.) In approximately 1905, the business was liquidated by transferring its assets to a new venture by Easton and his brother-in-law Warren Porter named Granite Rock Company. The firm is still in business today as Graniterock, which operates a large quarry on the San Andreas fault in Aromas, near San Juan Bautista.

The rock here was described by the state bureau of mines as “a blue metamorphosed sandstone” mixed with softer sandstone and shale that created a lot of waste. It is right at the edge of the Piedmont block of Franciscan sandstone, a district I described in more detail as the Oakmore block. Near the upper end of the school property, the rock walls are still exposed, as seen from Lincoln Avenue.

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Stone magazine reported in 1900 that Easton & Wilson was sued to stop from opening a quarry on Fruitvale Avenue, on the grounds that the blasting would “addle the eggs in the chicken ranches, which form the leading industry in the neighborhood.”

Apparently this ground sat for 60 years after the quarry closed. The Head-Royce School relocated to the property in 1964. The MacArthur Metro gave more details about the school’s history in 2013.

Harrington valley and ridge

22 February 2014

Harrington Avenue runs up a small valley cut into the Fan by a branch of Peralta Creek. It has a high ridge on its south side and a slightly lower one on the north side. Here’s the Google terrain map:

harringtonGmap

and the geologic map to match, marked with the sites of six photos. This part of the Fan is an odd flat area, which I call the Allendale Flat, crossed by several different streams separated by low ridges. The valley of Harrington Avenue holds the Harrington Branch of Peralta Creek. The watershed map posted by the Oakland Museum of California will help keep the streams straight. As for the topography, I’ll name the ridge on the north side Harrington ridge and the one on the south Jefferson ridge (part of lobe 6 of the Fan).

harringtongeomap

Harrington ridge is today’s geology puzzle. Its color stands for “Pleistocene alluvial terrace deposits,” and this is the only locality in all of Oakland, indeed the only one between Point Pinole and Hayward. It’s described as sandy gravel with boulders larger than a foot across (“35 cm intermediate diameter”). Only a very powerful river, or flow anyway, could have put such material here. My preference is to suspect a flooding event, given the dynamics of Oakland’s geologic setting: something like the sudden release of a large body of water. If you’re thinking what I am, Lake Chabot is about 5 miles, make that 8 kilometers, down the fault. At the rate the fault is slipping today (about 10 millimeters a year), the two features would have lined up 800,000 years ago. However, I haven’t seen any of this bouldery gravel because it’s covered with homes and yards. If anyone is excavating in the area, let me know.

This view is looking from Harper Street, on Harrington ridge, across the valley (behind the front row of houses) at its lower end.

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This view is from the top of Harrington ridge a block farther up, on Galindo Street. Looking straight down the left-hand sidewalk, across the creek, you may see the long stairway of Carrington Way climbing Jefferson ridge.

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And this is the view looking back from the top of that stairway (click to see it big).

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This next shot is from a point behind the previous one, zooming in on Galindo to show the crown of Harrington ridge (click for a big version). Note that it’s slightly lower than the rest of the Fan’s high points. The building with the colorful roof is the United for Success Academy on 35th Avenue. The four palm trees behind are on Galindo on the far side of Fruitvale Avenue, in the floodplain of Sausal Creek. The trees in front of them, I believe, are on the grounds of Patten University, across Peralta Creek. Behind them all is the Kaiser Center building, 3 miles away.

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This next view north is from one more block east, looking up Gray Street across the informal park called Jungle Hill. At least four homes used to sit here before landsliding took them out in the 1930s. (All I know about this is in a MacArthur Metro article from 2007.) Harrington ridge is relatively even lower here.

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And here’s a view looking almost due north across Jungle Hill and the upper end of Harrington ridge. The valley fades out of existence pretty rapidly as Harrington Avenue climbs out of it and enters the Allendale Flat.

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And there on the far right, as always, are the two ranks of high hills, one on each side of the Hayward fault. If you pick your spots carefully, Jefferson ridge offers a satisfying set of views around mid-Oakland.


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