Archive for the ‘oakland geology views’ Category

Rocks and land of south Mountain Boulevard

7 September 2015

First things first: I’m leading a “fieldwork-style outing” at Knowland Park on Sunday the 20th, from 2 to 4 pm. Details and tickets at Wild Oakland. This will be an experiment in having people learn about how geologists do their jobs and experience the landscape.

The southern end of Mountain Boulevard, between the zoo and the former Leona Quarry, is a little-traveled piece of road. I walked it the other day simply because I’m walking every road in Oakland, but it gave me a Eureka moment to share in this post. As usual, here’s the topography, with asterisks at the localities featured.


And here’s the corresponding geology. Jsv is the Leona “rhyolite,” which is actually a metamorphosed body of erupted volcanic material with a rhyolitic composition. This will come up again later. Jpb stands for Jurassic pillow basalt. They’re the two rock units I’ll be showing.


But first, a longing look through the fence at the empty piece of property where the Oak Knoll Naval Hospital once stood.


It looks like a peaceful valley, but the aerial view shows that it’s full of old concrete. When it gets redeveloped, which will happen some day, a portion will surely be kept woodsy. I hope the friends of nature are being vigilant about retaining as much habitat as they can here.

Also visible is the clubhouse of the short-lived Oak Knoll Golf Course that preceded the naval hospital.


There is little significant bedrock geology on the property, which is almost all Leona “rhyolite,” although how it managed to get so deeply eroded here is a puzzle. It would be interesting to get a look at the ground as it’s being excavated. The valley here is drained by Rifle Range Branch.


As is common in our relatively arid climate, the stream runs in a deep-cut bed or arroyo in a wider floodplain.

The second rock unit crops out along Mountain Boulevard at the western edge of the Oak Knoll property. It’s very different from the Leona and not really like the other brown rocks of Oakland either.


It’s mapped as pillow basalt, which is not at all evident right here. Basalt I can buy, although it’s pretty shattered by exposure and multiple tectonic insults since its eruption about 145 million years ago. Will definitely visit again for a closer look.

Farther north in the residential areas, you start seeing a lot of Leona rock in the landscaping, including some big boulders.


And I couldn’t resist a close look at this nice actinolite boulder across the street.


Farther north, Rifle Lane strikes up into the hills next to the Leona Quarry development. It’s secluded and rustic and full of rocks.


I also noticed a fair number of stones with greenish bits, which I’ve seen in many places in Oakland. This time I realized that they must originate in the Leona. Here are two examples. The left-hand one is from Dunsmuir Ridge, and the right-hand one is from a hillside on Outlook Avenue.


Clifford Hopson, one of the greats of California geology and a close student of the Coast Range Ophiolite of which this rock unit is a part, wrote in 2008 about these rocks, “Devitrification of once-glassy tuffaceous and fragmental siliceous rocks, including silicification that accompanied devitrification, accounts for their hard flinty character. Local turquoise-green beds mark pervasive celadonite, a typical low-temperature devitrification product of rhyolitic/dacitic tuff and pumice.”

And at the top of Altura Place is a colorful boulder of this stuff (1000px).


This rock superficially resembles the greenish metachert of the Franciscan Complex, shown here and here and here and here. But it forms in a fundamentally different way, and once you’re familiar with both rocks they’re easy to tell apart.

Encounter with Sugarloaf Hill

24 August 2015

As promised, here’s a look at Sugarloaf (a/k/a 1175) Hill. But first two announcements:

  1. The 46L bus line goes from the Coliseum BART station past the zoo to Oakland’s remote Grass Valley neighborhood. It’s the only public transit providing access to the area that includes all of Knowland Park. AC Transit funded a year-long trial of this route to restore service that was cut in 2010, when a transbay line served the area. It’s still a bit of a trek to reach the park, but for carless people it’s essentially impossible without the 46L. (Yes, the bus has a bike rack.) There will be a hearing on September 2 at an awkward time, 5 pm, to consider keeping the 46L going. That’s what staff recommends, but I will lobby the board to continue service because it’s up to them, not the staff. I hope you’ll speak up too. [Update: The AC Transit Board voted to make the route permanent.]
  2. Speaking of Knowland Park, I’m discussing the possibility of leading some geology walks up there next month, for Wild Oakland. Updates here and there.

Thank you.


Sugarloaf Hill is on the rear side of the Merritt College campus and is in the Leona Canyon Preserve. The East Bay Regional Parks District has plans to enable access to Leona Canyon when the college is closed, though it seems like a low priority for them.

The trail up the hill is not marked or mapped, but it’s not hard to find. As you go up through the woods, you’ll pass exposures of the Leona “rhyolite” that underlies this whole area.


Once above the trees, the campus unfolds below you. This shot also shows the range of habitats on the hill. (It’s a 1000-pixel shot; there are three more later in this post.)


The upper part of the hill is largely grassland with ferns and some bedrock. The soil is very thin. This land used to be grazed. The grassland, says the EBPRD, is dominantly non-native species. It doesn’t mention the ferns, considering them part of the forest biome.


Besides grassland, the hill comprises shrubland and oak/bay woodland. Some parts are pleasingly mixed.


The view west over Leona Canyon juxtaposes grassland and forest. The forest is typical coast live oak and bay laurel, along with buckeye and hazelnut and a whole bunch of different native shrubs. The houses are on Campus Drive.


And this view south over Leona Canyon shows the shrubland, consisting of coyote brush, sagebrush and poison oak. It’s quite overgrown. Absent grazing or fires, this tends to turn into oak/bay forest.


The rocks don’t form many outcrops, per se. There are abundant boulders like this one. They’re naturally covered with lichens, so you have to search to see any details of this metamorphosed volcanic sandstone. Please don’t take a hammer to this stone—besides being protected by EBRPD rules, it deserves to look the way it wants. (1000px)


The point of a hill, so to speak, is its top and the views it makes available. When I climbed Sugarloaf Hill it was a cool and hazy day, so the next two photos are just versions of what you might see from there. Here’s looking north toward the ridge of Redwood Peak, over the ballfields and solar array of Merritt College. (1000px)


And here’s looking south over Leona Canyon from the summit. The rectangle of boulders is I think the work of idlers rather than the remnants of an old foundation. On the horizon, from left to right, are the dimly seen Knife, the dark wooded ridge behind Lake Chabot, and tree-topped Fairmont Ridge behind the hills of Knowland Park. (1000px)


Your viewing may vary.

1175 Hill (Sugarloaf Hill), an Oakland local hero

17 August 2015

When I was writing for, I started a photo gallery of peaks. My philosophy was that there are lots of mountains besides the famous ones, like Mount Diablo, that are local heroes. Even a minor eminence can be the center of a neighborhood, and a hillock the heart of one kid’s fantasy world. I also entertained the idea that every hill and mountain is capable of being photographed in its heroic moment, so to speak — posed at a particular angle, in the right setting of weather and time of day.

Which brings me to 1175 Hill. You’ve surely seen it on the eastern skyline as you look past the Oakland LDS temple. I don’t know its local name, so I call it by its elevation, as shown on the local topo map. It’s part of our landscape.

Let’s circle around it, going clockwise. The photos were taken at various times during the last three years.

This view is from McKillop Drive across Sausal Creek. The palms are on Fruitvale at School Street.


Here it is in a view along Macarthur Boulevard in the Dimond district.


This view is from Skyline Boulevard at Serpentine Prairie.


This is from Bacon Road, looking across the big solar array in back of Merritt College.


Here it is from Skyline down around Lexford Place. We’ve gone halfway around the hill.


From the Artemisia Trail, down in Leona Canyon, the hill appears at its most imposing.


We can look straight up the hill’s axis from the top of Elysian Fields Drive.


From the west side of Leona Canyon, on the Pyrite Trail, is the last good glimpse of 1175 Hill. Houses along the ridgeline on Campus Drive get in the way, keeping the best views in their back yards.


And we close the circle at Merritt College. This is how the hill looks right next to the bus stop, a real ornament to the campus.


The hill has a city survey marker on its top, which is presumably where the elevation was measured. On topo maps before the 1959 version, its elevation is shown as 1168 feet, without a symbol. This signifies that its elevation was probably determined from stereo aerial photos. The 1897 and 1915 maps show it as no higher than 1120 feet. So I can say that as civilization approached and surrounded it, this hill has grown in our estimation. I hope with this post to further raise its esteem.

I’ll show you its geology and some views from its top next week. Until then, can anyone tell me if it has a local name? [Addendum: I now know that the Parks District knows it as Sugarloaf Hill, a common name across the whole country for steep, round-topped hills. See the comments]


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