Archive for the ‘Oakland geology views’ Category

Changes coming to Mountain View Cemetery’s landscape

4 July 2016

Mountain View Cemetery is one of Oakland’s great civic ornaments for several reasons: its gravestones and tombs commemorate generations of historically important Bay Areans, and its plan was Frederick Law Olmsted’s second significant large-scale project in landscape design after New York’s Central Park. It’s a fine piece of open space that’s used by many different groups of people.

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I think of the cemetery as a great civic ornament for two special reasons of my own. First, it’s a superb display of Oakland’s natural landscape as the first settlers knew it.

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Second, it’s got some great exposures of Franciscan melange, the mixture of rock types that was created by the tectonic collision between the North America and Farallon plates about 90 million years ago.

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The cemetery’s operators are planning to reoccupy and develop the highest part of the grounds, the two heights in this photo taken from the Catholic cemetery next door.

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Here’s the view from up there. The cemetery proposes putting in roads and formal structures in the foreground and up on the hill beyond the fence, behind the greensward.

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The goal is to accommodate about 1500 more grave plots. A lot of dirt and rock will be dug up and moved around. The plan talks of building up the hilltop and tilting it toward the bay for better views.

The city’s master page for the proposed work is here. The draft environmental impact report is there, plus info on two upcoming hearings (July 11 for the Landmarks Preservation Board, July 20 for the Planning Commission). This month is the public’s most influential time window.

The land beyond the fence is a special bit of countryside . . .

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. . . with its own constituency.

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It also has its share of rock outcrops. To me these are precious things. Most outcrops in these hills either were blown up during development or are locked up in people’s back yards.

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I’m still thinking about what I want to tell the city. But my basic concerns are that the natural character of the land — its contours and vegetation — be respected and preserved as much as practicable. The project will affect a landmark that hundreds of thousands of people enjoy from their own windows and yards.

Olmsted considered these hills the essential setting for the elegant, transformative parkland he planned here in 1863. Mountain View was, and remains, an icon of the City Beautiful movement and a destination for landscape architects everywhere. It and Stanford University (designed in 1888) are the only major Olmsted projects in the Bay area.

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This amazing cemetery is Oakland’s cemetery. Let’s speak up to help keep it as beautiful as possible.

Faceted spurs along the Hayward fault

20 June 2016

A lot of geology involves glimpsing the ideal behind the real. As you look around Oakland, the Hayward fault isn’t easy to see without a bit of training. For this post, let me start you from the ideal. The process of faulting has very specific effects on the land that you can learn to look for, then see.

Motion on the Hayward fault is mostly sideways, but a small proportion of its motion is compression across the fault. Compression has been pushing up the east side of the fault for at least the last million years, building the Berkeley/Oakland Hills. Where streams cut their valleys across such a fault, the ideal result is something like this example from the Manti-La Sal National Forest, in Utah. The image is from the Open Topography site and is derived from lidar (laser “radar”) data.

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The flat, triangular faces of hillside are called faceted spurs. As you look at this, imagine the motions and processes that create the landforms. The high part is being raised; the streams are cutting downward; the low part is sinking while the streams dump their sediment onto it.

That’s about as geometrically perfect as faceted spurs get. In Oakland, they’re much more subtle. The rest of the images in this post are large; click each one to see it full size. Here’s a 1000-pixel view looking north from the top of Mountain View Cemetery.

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The numbers are as follows: 1 is the north side of Claremont Canyon, 2 is the south side, 3 is Grizzly Peak, 4 is Hiller Highlands, and 5 is the nameless ridge (Powerline Ridge, I guess I’d call it) south of route 24 as you approach the Caldecott Tunnel. Except for Grizzly Peak, those are faceted spurs.

Here they are labeled in the 1915 topographic map, made before the Caldecott tunnel construction changed the hills. The asterisk is where I was standing.

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I’ve also marked them in this view from above in Google Maps, turned so the fault runs straight across the image.

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And finally, here’s the same view in Google Earth, including the lidar data along the fault. The beauty of lidar data is that you can digitally subtract buildings, trees and so on to show the pure shape of the ground.

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Do these help you see? I hope so. There are other faceted spurs in Montclair and around Sheffield Village, at the far east end of Oakland.

Rocks and views of Fairmont Ridge

2 May 2016

Fairmont Ridge is the grassy upland that forms the backdrop to San Leandro. As it happens, East Bay Regional Park District owns much of it as part of Lake Chabot Regional Park. It has some rocks, which I’ll show first, and also some fine views.

Here’s the aerial view of the ridge from Google.

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And the geology of the same area is here.

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We’ll look at rocks from three different units: the green area is underlain by the Knoxville Formation, a shaly sedimentary unit; the light-brown area labeled Jpb is basaltic lava; and the pink area labeled Jsv is Leona rhyolite, which you’re familiar with by now from Oakland.

The Knoxville is well exposed around Lake Chabot. Here, to the east of the access road at locality 1, it appears to be strongly sheared, suggesting that its contact with the structurally underlying Leona and basalt is a fault. This view is facing north, parallel to the contact.

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The basalt unit is formally described as pillow basalt, the kind of balloon-shaped flows you’d find where lava erupts beneath seawater. But these rocks have been shoved around a lot since they were erupted in Late Jurassic time, and I have yet to see decent pillow morphology in any exposures. Still, the outcrops, like this one at locality 2, are picturesque.

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The windbreak of giant, mature eucalyptus is visible in the photo. This is a naturally breezy park, and the line of trees offers some welcome shelter.

Across the ridge on the Bay side, there are more outcrops of the basalt. Around locality 3 it’s well displayed.

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If you pay attention, you’ll see bits of this rock with polished surfaces, or slickensides, on them. These are caused by motion on faults, which rubs rocks against each other. Here and there, proper outcrops enable us to see that the faults are oriented vertically and parallel to the ridgeline. I interpret these as forming recently as these rocks were folded and tilted upright by motion related to the Hayward fault.

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The peak of Fairmont Ridge is fenced off, but an informal trail leads north along the east side of the fence to locality 4. (Poison oak will very soon make it impassible.) That’s where this typical specimen of Leona rhyolite was.

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But sometimes rocks are just rocks. Lift up your eyes from the hills and sit a spell. You can gaze upon the Bay side . . .

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. . . or over the reservoir toward Mount Diablo.

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Looking due east is a nice prospect of the ridge known as The Knife, overlooking San Ramon.

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Its high point is named Wiedemann Hill, elevation 1854 feet, and I have a growing fixation with it.