Lava rampart at Grizzly Peak

The other week I noticed a big outcrop of basalt of Moraga Formation right next to Grizzly Peak and remarked that it would be worth a visit. And so I did, while preparing my post for KQED Quest Science Blogs last week on the Moraga Formation. It’s easy to reach from a couple of different pullouts on Grizzly Peak Boulevard. Here’s a view looking south.

The rock is thoroughly covered with lichens, so you can’t tell much about it, but it appears to be a massive flow of lava that, like all the rocks in the Berkeley/Oakland Hills, has been tilted nearly upright with the top toward the northeast. Stratigraphically above it, beneath the road, it’s mapped as sedimentary rocks associated with the Moraga Formation. The area was a lake or wetland at the time, about 9 million years ago, with high hills on the west where the Bay sits today. And on the other side of the road, including Grizzly Peak itself, the bedrock is the Bald Peak Basalt, a slightly younger volcanic unit.

Here’s a better view of the west face.

There’s quite a large rock face exposed on that side of the lava bed, but almost nothing exposed on the uphill side. The rock has a lot of paint on it here and there, including some marks that look like rock-climbing instructions. The rock is pretty sound for climbing, but be careful anyway because its strong exposure to sun and weather can weaken this basaltic rock without showing. (The rhyolitic rocks in Berkeley proper are better that way.)

It’s a well-used outcrop, but still, please don’t take a hammer to it as it’s located on UC Berkeley land. It’s the headwaters of Strawberry Creek.

Here’s the view back to the place where I first spotted this feature: in the row of trees just to the left of the rock.

Grizzly Peak and Moraga basalt

In northernmost Oakland is the small, steep Panoramic neighborhood, which perches on the high ridge between Strawberry and Claremont canyons. At the top of Panoramic Way is this view north across Strawberry Canyon to Grizzly Peak, which at 536 meters (1758 ft) is the highest point in Oakland. Click the photo for a 1000-pixel version.

The bottom of the photo grazes the UC Botanical Gardens. The lowest slopes in this view are underlain by the Claremont chert, up to the powerline tower directly below the peak. Above that is the Orinda Formation, and the ridgeline is lava of the Moraga Formation.

To the right of the peak, on this side of Grizzly Peak Boulevard, is a big, towering outcrop of basaltic lava; here’s a closeup.

That seems like it would be worth a visit, if the poison oak isn’t too bad.

Oakland EarthCaches

When it comes to exploring Oakland’s rocks, I’m pretty self-sufficient, once I’ve consulted a map. I don’t mind a climb or a scramble, and I can find little geeky things that interest me pretty much everywhere. But for most people, rocks are unfamiliar things that don’t have obvious messages. Maybe those people are more comfortable at home in familiar surroundings. Even a nearby place like Round Top, an everyday sight, seems better admired at a distance.

People need other people to show them geology. Here’s a new way to make that happen. EarthCaches are a kind of geocache that don’t require you to find a hidden box and trade a trinket; instead, they’re places to stand, specified by a precise GPS setting, where you can read a prepared lesson about the geology of that spot. Learn more about them at earthcache.org.

There are more than ten thousand EarthCaches around the world, each one vetted by geologists through the Geological Society of America. As of today, there are seven in and around Oakland:

Round Top
Orinda Formation on Skyline Drive
Orinda and Moraga formations east of the Caldecott Tunnel
Rhyolite above Claremont Canyon
Claremont Chert (you’ll find this familiar)
Spheroidal weathering in Briones Park
Shell Ridge, Walnut Creek

Seems like there could be a lot more.

And now: Oakland in stereo

I’ve been away in Denver, at the Geological Society of America annual meeting, plus a few days in the Rockies, so haven’t posted lately. And naturally I caught someone’s cold germs along the way, so I’m feeling pretty lousy. Let’s try a trick that geologists are trained to do: viewing stereophotos without a viewer. This is a pair of shots I took showing “Mount Ararat” in upper Broadway Terrace. It’s my personal candidate for the original Rockridge Rock. Click on the image for a much larger pair.

You get the stereo effect by crossing your eyes until the images fuse, then directing your focus onto the fused image. This example is a little strong. All I do to make them is take two shots, first leaning left, then leaning right. I give more detailed instructions for viewing stereopairs and some examples on my About.com site. If the effort makes your eyes ache, now you know how I’m feeling at the moment.

Big Rock

I was at Temescal Regional Recreation Area yesterday—you probably call it Lake Temescal—and was happy to spot one of my favorite places.

This big hunk of Franciscan something-or-other sits near the head of the lake, displaying the ugly attractiveness that the French call jolie laide. Not a hundred feet away runs the Hayward fault, and there’s a free-running stream here too. Some classic oak trees shade picnic tables, and you can even swim where fish can nibble your toes.

Big Rock is the place I used to illustrate my post “Leave the Stone Alone.” Because for some reason, people seem to respect Big Rock.

Views: Mira Vista

Every now and then I’m gripped by a charming view, like this one from Mira Vista Avenue.

Click it for an 800×700 version. We’re looking east across the valley of Pleasant Valley Creek, which runs under Grand Avenue, to what I call Warfield Ridge. That ridge and the foreground are on the big Pleistocene alluvial fan that stretches from Pill Hill to Evergreen Cemetery. Little bits of upper Piedmont (Franciscan sandstone) are also visible, and behind it all is the Oakland Hills (Tertiary sedimentary rocks), including Redwood Peak at its highest point.

This is a great time of year to walk around Oakland, if you can make the time.

Before you take that walk, please contact your state assembly member about Senate Bill 624, which would remove the state rock. It’s on the floor now. Geology teacher Garry Hayes has been indefatigable in the effort to defeat SB624; his latest post today is a masterpiece.

Twin peaks

There’s a wedge of land between the southern end of Grizzly Peak Boulevard and Skyline Boulevard that belongs to the Sibley Preserve. (It’s the little knob on the left edge of this blog’s banner image.) It has good views all around, like this one looking north-northwest. Click the photo for a larger version.

The peak on the left is Grizzly Peak, 1754 feet high. The peak on the right is Vollmer Peak, 1905 feet high. Both consist of basalt. Grizzly Peak’s rock is basalt of the Moraga Formation, the same stuff exposed in upper Claremont Canyon and in Sibley itself. Vollmer Peak is held up by a slightly younger unit, the Bald Peak Basalt. The bulge between is Chaparral Peak; it and Grizzly are part of Frowning Ridge, which ends in the green ridge below Vollmer Peak in this photo.

Grizzly Peak appears to be unambiguously part of Oakland, nestled in a sliver of territory between the UC campus and the county line. It isn’t Oakland’s most northerly bit of land, though. Another bit lies north of Grizzly Peak Boulevard and Golf Course Drive. I’d like to visit both spots.