Archive for the ‘Oakland peaks’ Category

Vollmer Peak and the Bald Peak Basalt

11 April 2016

At 1905 feet above sea level, Vollmer Peak is the highest point on San Pablo Ridge and in the Berkeley/Oakland Hills. It doesn’t stand out from below — you know it by the two widely separated towers on it, to the right of Grizzly Peak — but it sure stands out when you’re on it. Here’s a view of Grizzly Peak from its upper flank.

griz-from-vollmer

Vollmer Peak used to be known as Bald Peak, which accounts for the name of the rock unit that holds it up. The Bald Peak Basalt is the youngest volcanic rock in the Oakland area, the well-defined reddish blob in the geologic map labeled Tbp (for Tertiary Bald Peak).

vollmer-geomap

I haven’t seen a lot of this rock, but it’s described as “massive basalt flows.” Here’s an example from nearby Chaparral Peak. Notice the dark color and the light-brown weathering rind, both of which are typical.

BPbasaltfromchap-peak

Its age, about 8.4 million years, is distinctly younger than the lava flows you’ll see at Sibley Volcanic Reserve, which are part of the Moraga Formation (Tmb) and date from 9 to 10 million years ago. The two volcanic units are separated by sedimentary rocks of the Siesta Formation, and apparently the Bald Peak and Siesta interfinger with each other in outcrops in the upper part of the Siesta Valley.

It’s nice and quiet up there, and the wildflowers are in progress. The peak used to be unforested, like all the high hills, and it has remnant populations of many different meadow plants.

Here’s a shot overlooking Briones Reservoir on a moist day. In clear weather the Sierra Nevada takes precedence.

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And here’s the view southeast. There’s a lot to point out in it.

vollmerviewSE

Left to right on the horizon, we see the flank of Mount Diablo, the twin humps of Las Trampas Ridge and Rocky Ridge with Bollinger Canyon between them, the Diablo Range hills beyond the Livermore Valley, and Round Top on Gudde Ridge. The green valley in the middle is Wilder Valley (or Gateway Valley) in Orinda, now being developed. It’s the counterpart of Siesta Valley on the north side of route 24, which we can’t see because we aren’t high enough. The tree-studded hilltop in the middle is Eureka Peak.

Basalt at the foot of Frowning Ridge

16 November 2015

I took this photo last Tuesday, the day after our nice good rain. If you weren’t outdoors last week, you missed a brief moment in the Oakland year that lasts just a few days.

1684hill

It’s the period between the first significant rain and the sprouting of the grasses.

(Before I continue, this is the last week of the scientific blog survey, to which you’re invited to respond at bit.ly/mysciblogreaders. There are prizes, plus the good feeling of helping research. More than 100 of you have already taken part.)

The first rain drenches the ground and changes the dry, gold-brown hillsides to a rare saturated dun color. Soon afterward the hills flush green, and we’re off to a new year in the Mediterranean climate cycle that governs the Bay area. Think of it like the week between Christmas and New Years, only it’s in the calendar that plants use.

This is a special hill at the southern end of Frowning Ridge, the highland that includes Grizzly Peak and its lower, gentler neighbor Chaparral Peak. Old topo maps mark it with its elevation of 1684 feet. To the right of this photo, shot from Skyline Boulevard near Radio Tower Hill, the ground plunges to the water gap and roadcut of Route 24. On the other side of 24 the ridge resumes, under the name Gudde Ridge, and rises to the peak of Round Top. The following shots from 1684 Hill are from a visit in July 2013, during the gold season of the plant calendar.

1684-view-south

Frowning Ridge is held up by the thick lava flows of the Moraga Formation. Like most of the rocks in the Oakland/Berkeley Hills, the Moraga Formation is tilted up to nearly vertical. You can reach 1684 Hill by an informal path off the Skyline Trail. The lower western slope of the ridge is underlain by Orinda Formation conglomerate, but basalt makes up its bulk.

1684-moraga-basalt

Let’s look back west toward Radio Tower Hill. Last week’s photo was taken from the little saddle at the left edge.

1684-view-west

The view north takes in the upper part of Siesta Valley. That’s Vollmer Peak in the middle, highest point in the Berkeley Hills. Grizzly Peak is just out of sight at the left, but the tip of its radio tower shows.

1684-view-north

The view east overlooks lower Siesta Valley and Mount Diablo.

1684-view-east

On a clearer day I imagine the Sierra Nevada is visible along the left horizon.

Encounter with Sugarloaf Hill

24 August 2015

As promised, here’s a look at Sugarloaf (a/k/a 1175) Hill.

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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.

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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.)

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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.

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

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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.

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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.

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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)

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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)

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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)

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Your viewing may vary.