Archive for the ‘oakland geology views’ Category

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.


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 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.


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.


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


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.


The view east overlooks lower Siesta Valley and Mount Diablo. On a clearer day I imagine the Sierra Nevada is visible along the left horizon.


(Again, it would be really nice if you participate in the survey of science blog readers at There are prizes, and November 20 is the last day. Thanks.

(This will be the last time I promote this study, so next week we’ll be back to normal. I’ll follow up in the Q&A/Announcements thread. Here’s the full announcement, one more time:

(Help us do science. I’ve teamed up with researcher Paige Brown Jarreau to create a survey of Oakland Geology’s readers. By participating, you’ll be helping me improve this blog and contributing to SCIENCE on blog readership. You will also get FREE science art from Paige’s Photography for participating, as well as a chance to win a $50 gift certificate, t-shirts and other perks. The survey should only take 10-15 minutes to complete.)

Read Oakland’s landscape on public transit

9 November 2015


Last Thursday I finished a long project in which I walked every block of every street in Oakland, both sides. I did this largely using public transit — our stalwart AC Transit buses and our intrepid BART cars. Both of these systems offer good vantage points to appreciate Oakland geology.

The buses give riders nice views of the hills and the bay, if you keep your eyes open and make the most of glimpses. A day pass is five bucks, and if you have a Clipper card it’s less, and if you’re of senior age it’s even less. Usually the windows are clean, and the landmarks visible en route will keep you with a sense of where you are.


The backbone routes, good for sightseeing, are the 1, the 51A/B and the 57/NL/58L. From them you can get up to the hills via several rib routes — the 11, 18, 39/339, 54, 45 and 46/46L. And that’s the real beauty of public transit, the fact that it can take you out to the land, not just in to town, work or school. And with various amounts of walking or cycling, you can then wander your fill among our rocks and scenic neighborhoods.

Then there’s BART. The windows aren’t clean often enough, but when they are the trains offer extended views of the hills with the rare advantage of continuous motion, which helps in sorting out the hills. I never tire of that.

The BART stations, conveniently, connect with the bus lines. But if you’re early for the bus, or early for the train, they’re also the best places to photograph the hills, or study them with binoculars. And here I want to give the Fruitvale station parking structure, where this shot was taken, an honorable mention.


The BART stations are the best public places to capture picture-postcard photos of the Oakland hills. The Rockridge, MacArthur, West Oakland, Fruitvale, Coliseum and San Leandro stations each have their own charms.


This winter ought to offer views that are truly more picturesque. A sky with clouds, if you get the light right, is lovelier than a big blank blue sky. And misty days can bring out the true depth of our hills, ridge upon ridge.


Urban geology, just like geology out in the country, depends on deep knowledge of the land. That comes from extended visualization, seeing the land from all angles; and from what I might call extended visceralization, walking on the land in all directions and feeling it in your bones.

Watershed wilderness

5 October 2015

The lower end of Skyline Boulevard offers a tantalizing glimpse of the wilderness right next door. This post has large images, so I encourage you to click on them.

When you look east from most of Oakland’s highest hills, the center of attention is Mount Diablo. You can drive there and drive up and it’s a wonderful place. From the southernmost end of the hills, though, Diablo is hidden by Rocky Ridge.


Rocky Ridge reaches just over 2000 feet elevation and forms the west side of Bollinger Canyon, in Las Trampas Regional Wilderness. Between here, at the city stables just north of Keller Road, and Rocky Ridge lies Grass Valley, with its patches of grass and a power line running up it; then a darker, more distant ridge on the other side of Upper San Leandro Reservoir. From there to Rocky Ridge is an untrammeled area of mixed woods and fields and chapparal that’s East Bay MUD watershed land.

The ridge is about 5 miles away in a straight line but more like 8 miles on foot. With a permit, you can walk there but you can’t bike and you can’t camp. In a word, reaching that land from here is a pretty extreme challenge. You could reach it from the other side if you’re up for an 800-foot-plus climb out of Bollinger Canyon.

It’s so near, yet so remote.

Here’s the geology: fairly young sedimentary rocks, of late Miocene age (roughly 10 to 5 million years old), deeply folded to create dramatic exposures on Rocky Ridge’s flank. Don’t worry about all the symbols and labels, they’re significant only to a few specialists.


The photo is taken from the lower left corner where it says “Ko” (for the Oakland Conglomerate) and points toward the upper right corner. In the upper right quadrant, that set of stripes with the heavy line on its right edge represents the package of rocks making up the ridge, and the heavy line marks a thrust fault along which those rocks have been uplifted.

To help you visualize what the map is showing, the map includes a cross section of these rocks, drawn along that straight diagonal line near the top left. The point labeled B’ corresponds to the same point on the cross section, below.


Is your brain stretched to breaking yet? No? You may have the makings of a geologist.

For a much easier experience, hike in Grass Valley instead. That’s not watershed land, because it drains into Chabot Reservoir; instead it’s in the northern part of Anthony Chabot Regional Park, where only the locals go, and is as peaceful as can be. Some day I’ll post about it.


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