Archive for October, 2008

High points

29 October 2008

kaiser center parking lot

For the best sense of an area’s geology you need to see it at as many scales as possible. I study this city from eye level and ground level, also by staring at maps. I climb its hills and go beyond its borders to survey it from a distance. If I had a light plane, I’d cruise all over from a thousand feet up. (In its absence, Google Earth and Google Maps are quite useful.)

Another of my practices is to climb parking structures. The views are always good, but nobody else does this—these buildings aren’t reaching their full potential! This shot is from the top of the Kaiser Hospital’s parking structure during a spectacular sunset in the winter of 2003. That’s Piedmont Avenue below. Round Top pokes above the large apartment building at center right. The knob at farthest left is now occupied by a very large house, looking down on the rest of the Hiller Highlands. Imagine having a public park bench up there.

Knocker nine

22 October 2008

knocker 9

I don’t know why I call this knocker nine, since the last set of Mountain View Cemetery knockers I posted should be number 8 through 11. But I can be inconsistent in my domain, and besides I think it just looks like knocker nine. This mini-outcrop in the Franciscan mélange is on Piedmont town land, on the hillside above the skateboard park south of the cemetery. The rocks are no respecters of property lines or jurisdictions.

I’m headed out of town for a few days, so talk amongst yourselves if you like. I’ll be in Las Vegas and enroute by car, taking a loop down into deepest Imperial County.

Earthquake day II

20 October 2008

hayward fault earthquake

October 21 is the date of the 1868 Hayward earthquake. It was on the order of a magnitude 7 and caused widespread destruction plus a couple dozen deaths. Over the last 2000 years, the Hayward fault has had large earthquakes at an average of every 140 years, and this year marks 140 years since 1868. There will be a public gathering on the 21st, at the Mission San Jose, at 7:55 a.m., the time of the quake. (At least it wasn’t at 5:13 a.m. like the 1906 quake.)

Unfortunately the officials are making the same mistake the San Franciscans do, which is to ignore daylight saving time and time zones generally. In 1868, cities determined their time locally from astronomical noon (or used the time of a larger regional city), so the contemporary time must be adjusted for us to experience the setting of that earthquake at the correct time of day. I don’t happen to know if Hayward used San Francisco time in that year, or if both cities used Sacramento time. In 1906, California was on Pacific standard time year-round, and 5:13 a.m. on April 18 was nearly sunrise, but nowadays they observe the moment, in a ceremony at Lotta’s Fountain, in the dark of night an hour earlier.

Oh, the photo? It’s the little valley across the freeway north of the zoo, where Arroyo Viejo makes a right-hand jog as it crosses the Hayward fault. We’re looking across the fault from Calandria Avenue in early 2005. The hill on the far side is a shutter ridge, cruising north at a long-term rate of about half an inch a year, which it does in meter-sized jumps every couple centuries. (It moved in 1868.) The hill has a large covered reservoir on top of it, to the left of this photo; you could easily imagine it rupturing in a large quake. That doesn’t mean it will rupture, because it’s well engineered, but it’s easy to imagine it failing. In the middle is Holy Redeemer College.

Earthquake day

17 October 2008

cypress structure mandela gateway

October 17 always has an ominous ring to it, because of the Loma Prieta earthquake of 1989 (or “the big-enough one“). In Oakland, we were distant from the epicenter, which is just visible on a clear day in the mountains beyond San Jose. But it was on this spot where the double-decker Cypress Structure, part of the Nimitz Freeway, felt its soft ground give way and collapsed, the deadliest single place in the whole disaster. I remember riding BART into the Oakland West station (remember when they called it that?) and sensing the whole carful of riders hold its breath as the wreckage came into view.

It was an ugly, traumatizing mess for years and years. In 2005, when I took this photo from the BART station on January 28, the Mandela Gateway complex at the base of Mandela Parkway was new, landscaping along the road was under way, and the area seemed nearly finished. But if you know where to look as you ride west from the downtown stations, you can still see the curved trace of the old freeway in the lines of the buildings and lots. Earthquakes are forever.

Fun with stones

14 October 2008

stone pad

I keep my eye on the ground all the time, including people’s yards and walks. Old homes favor local stone, for example, because it was quarried here at the time or maybe because people used to dig around their property more. People were more self-reliant in the past, too—the ability to do carpentry, tend animals and maintain buildings was more common. New homes all use imported stone, often lava rock from northeastern California that looks as foreign here as Carrara marble. Others favor mossy boulders that are ripped from a distant, anonymous hillside somewhere or perhaps even harvested illicitly from a national forest. No one certifies gravel, after all.

But in this driveway panel at the top of Howe Street, these all look like local rocks, put together by someone who saved a pile of them just in case. If I owned my house I’d make something like it. Whoever created this didn’t drive down to American Soil Products and order a yard of pink flagstones first.

Leave the stone alone

9 October 2008

temescal park

Oakland is in an unusual situation. Right now, nobody is exploring Oakland geology, yet the city has a great variety of features worth attention and even celebration. I’d like to see that change, which is one reason I began this blog just over a year ago. Right now, Oaklanders are spreading their attention on fresh culture, the creeks, the government, business, the lake and their houses and families and neighborhoods. People are outdoors—I see them almost everywhere I go—but nearly all of them are either construction crews, joggers or bicyclists. They aren’t there just to BE there. (Maybe I’m not either, strictly speaking, but let’s let that go.) Even if they set out to enjoy some of Oakland’s geology, there are no trails and almost no interpretive exhibits. And even if there were trails, I’m not sure I would favor that because development brings degradation. Let me give an example or two.

Mount Tamalpais, in Marin County, gave rise to mountain biking, starting in the seventies with a close fraternity of obsessive amateurs. Today the sport is an industry that benefits many thousands of people, some of whom—just a relative few—are poor citizens that blaze unsupervised trails and abuse existing ones where they are prohibited. The rocks of north Berkeley, most notably Indian Rock, spawned a lively school of rock climbing starting with the David Brower crowd in the 1930s, and today Berkeley’s public crags are so overrun with exercisers of all ages that visiting for any other purpose is difficult.

All this is just to say that if the geologizers of Oakland are ever to increase in number and sophistication, we have to build in righteous field manners, responsible enthusiasm, at the foundation. For the Oakland amateur, the city’s landscape is as good as a wilderness, and my own practice is evolving toward the wilderness ethic of the Sierra Club: take only pictures, leave only footprints. For some time to come, Oakland geologizing will be, not exactly underground, but unsupervised. And because “to live outside the law you must be honest,” I want to set a personal example of self-restraint.

And so one of my watchwords as I traipse about our streets and slopes is “leave the stone alone.” We aren’t real geologists, with a job to do that requires us to sample and hammer and drill the outcrops. We’re just out there to enjoy and learn, and I believe we should treat Oakland, for the most part, like a park. Everything I show you here in this blog is something I’ve left behind unblemished, so that you can enjoy it just as much.

Shale concretion

2 October 2008

shale concretion

Just up the hill from the Paleocene sandstone I was looking at last week, on Woodrow Drive, all sign of bedrock disappears. But I kept looking and eventually spotted a dark pod of rock—a concretion. I banged it open and this is what I saw.

The piece in the middle shows the dark outer surface, probably a thin layer of iron or manganese minerals. To its right and above it is the core of the concretion. Its outer surface was pure clay that stained my fingers and got all over my pants. But the definitive field test is to nibble it. Pure clay, as found in shale, is not gritty but smooth as chocolate against the teeth. A mudstone or siltstone is definitely gritty. (Mudstone is a sedimentary rock with a mixture of particle sizes, clay and silt and sand.) And of course, sandstone you just don’t bite.

I don’t know much about concretions, really. Some have an obvious fossil or foreign stone in the center, which releases or attracts elements that create shells of harder minerals around them. In others, I suppose the central object dissolved away completely into the outer layers (this one had none). They can be little things or a meter or more in size. Bowling Ball Beach, up in Sonoma County, is full of them.

Anyway, this concretion told me that the rock along this part of Woodrow Drive is really shale, even though it’s hidden. Shale turns back to clay so readily that you don’t get good exposures of it except in a fresh roadcut. The rock here is mapped generally as Eocene mudstone, Eocene meaning about 55 to 35 million years old.


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