Archive for the ‘Oakland peaks’ 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.

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.

vollmerviewE

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.