Archive for the ‘Oakland geology views’ Category

South Dunsmuir Ridge

29 May 2017

I finally got to a sweet corner of town last week, the sunny side of Dunsmuir Ridge, this lovely hill in the Google Maps 3D view.

The view is to the north-northwest, such that the Hayward fault runs straight up about a thumb’s width from the left edge. The maps below start with the 1915 topo map, in which the ridge’s top is the lobed outline of the 625-foot contour.

That straight creek valley along the hill’s south side — the gorge in the foreground of the top image — keeps catching my eye, but it seems to be inaccessible, which might make it Oakland’s wildest piece of land. The watershed map below may help in visualizing the hill and its surroundings. The two black dots are where the fire trail I took starts and ends.

Dunsmuir Ridge is city land, rescued from development after several aborted attempts to put high-end estates on this broad hilltop overlooking (in both senses) the deadly Hayward fault. The fire trail starts at the end of Cranford Way and winds up the ridge to join the fire road from the other side, which I’ve featured here before.

The walk is very scenic. To the north, downtown rises against Mount Tam.

Or if you prefer, there’s the new profile of San Francisco.

Higher up, the view opens out. Here San Leandro Creek is made visible as a line of trees coming out of the canyon toward its mouth near the airport.

But the main attraction is to the south. This is the best place to take portraits of Fairmont Ridge and its quarry scar. Unlike most places, this trail sets off the hill with a foreground of wild, forested land.

The prominent cleared space midway up the trail — a staging pad for firefighters — has regular visitors who find the spot special.

Interestingly, this spot is mapped as a patch of the peculiar Irvington-aged gravel that first brought me to Dunsmuir Ridge in 2009. However, I didn’t notice much of it, if any. See it on the geologic map — the white dots mark the ends of the fire trail.

There are rocks to be seen too. The soil is thin in most places. This little cut displays a profile of the soil and the decaying bedrock — saprolite — just beneath it.

The bedrock varies, and it doesn’t match the geologic map very closely. I would say nearly all of the lower part is not Leona volcanics (Jsv) but San Leandro Gabbro (gb). It has the gabbro’s pepper-and-salt appearance but is stained orange instead of the pristine rock’s bluish gray (as I saw earlier that day in San Leandro). You’ll see it well exposed in the trail itself, where this winter’s heavy rains carved fresh runnels.

If the city fills them before you get there (which it should before they become gullies), there are still roadside exposures that display the rock well, and it’s unmistakably gabbro where the map says volcanics. The top of the hill, though, is unquestionably Leona volcanics.

My long-term plan is to revisit every bit of bedrock in Oakland and log it. Besides sheer nerdery and the chance to improve the map, my motive is to come back to views like this one over and over again.

The old quarry is still for sale. Developers have tried to put houses there, but they keep getting shot down. Better, I say, for the Regional Parks District to acquire the land and develop it for quiet recreation.

Mountain View Cemetery: The Bay area’s best landscape

1 May 2017

Although I’m tempted just to let the photos in this post stand on their own, let me make a case that Mountain View Cemetery offers the best landscape in the Bay area.

First there’s the cemetery itself. The managers have been putting a lot of effort into improving the ground — see the excellent new stonework and gravel path in the first photo — and this winter’s abundant rainfall has abetted it by giving the hills a coat of green that ought to last longer than usual before turning gold, then brown.

Unlike your typical cemetery, Mountain View is very large and occupies the rolling terrain of the Piedmont block, consisting of Franciscan melange. In the photo below, all of the land in sight lies within the cemetery’s property.

Long ago the operators arranged for Cemetery Creek (headwaters of Glen Echo Creek) to fill three ponds, where the water can be parceled out over the dry season to help keep the turf lush. Right now they’re brim full and support a few waterfowl. The open hilltop on the left side will be turned into a new section of graves under a proposed plan.

The Franciscan outcrops or “knockers” in the cemetery’s hills echo the finished stone displayed so touchingly in the grave markers. Many historical Oaklanders famous and obscure rest here. A random walk in any direction will bring up names that ring a bell if you’ve spent significant time in the East Bay. Yes, that’s what cemeteries are for, but without the graves this territory would be just another busy park. The dead ensure that the living visitors stay on their best behavior.

And this is important — the delights of the cemetery don’t stop at its edge. The east side has had its huge hedge of overgrown eucalyptus removed, opening the crest of the high hills and the well-tended neighborhoods of Broadway Terrace to view.

A few eucalyptus trees remain on the hilltop hosting the cemetery’s high staging area. In manageable numbers, their trunks are attractive as they frame views of tempting places.

With the view east restored, there’s now a postcard vista in every direction you look. To the west you can see the Golden Gate, San Francisco, St. Mary’s Cemetery and Oakland’s outer harbor.

To the southwest is downtown Oakland and the ridges of the San Mateo Peninsula. These views, as well as those to the north and south, will always be unspoiled. From Mountain View, one can take in surroundings that encompass a large share of the greater Bay area from the midst of a setting that’s both attractive and historic.

So that’s my main case for this being the Bay area’s best landscape. But there’s more — there are rocks. I always make sure to visit this outcrop of red-brown radiolarian chert on the hillside behind the garden mausoleum, plot 3.

Other parts of the cemetery consist of shale, like this bit left behind from an excavation in plot 9.

The road up to the top of the cemetery exposes some of the well-bedded mudstone that underlies much of the grounds, but look in the gutter for the freshest exposure.

And once up there, make your way bayward from the northern tip of plot 77 to this outcrop of green and red chert.

I’m glad to entertain arguments that one place or another might be superior to our cemetery. For sheer viewshed, Mount Diablo is a candidate, as is Tamalpais. Twin Peaks in San Francisco gives excellent views of Oakland. Mount Livermore, on Angel Island, is worth a special mention. The South Bay and North Bay have many more picturesque places, not to mention the Peninsula. Lots of these spots survey a more spacious territory, but Mountain View surveys the most gracious territory, a viewshed of singular integrity that extends from infinity to your feet. In a region full of landscapes, this one offers as much elegance as it does grandeur.

The marine terrace of Clinton, lengthwise

20 March 2017

A few years back I showed you a view across the flat marine terrace where the old town of Clinton once sat, back in the 1850s. To really get a sense of it, walk the length of the terrace some time. Here it is on the geologic map, marked “Qmt.”

The photos below (1000 pixels) were taken last week at the locations of the two blue asterisks.

First we have a view off the edge of the terrace at E. 15th Street and 22nd Avenue. At barely 40 feet elevation, the view is quite extensive. That’s the former Catucci building in the left middle.

East 15th Street, a residential street running between International (E. 14th) and Foothill (E. 16th) Boulevards, is a pleasant walk on this extremely level geomorphic feature. Look northeast as you go and note the abruptness of the terrace’s inner edge. That was where the sea used to lap up against the Fan during the last major interglacial, about 125,000 years ago.

At the other end of the terrace, at 3rd Street and Foothill, the land turns down toward Lake Merritt (and the hospitable Portal).

But turn around to see just how flat this thing is.

The two stream valleys that interrupt it, at 14th and 23rd Avenues, are like canyons by comparison.