Archive for May, 2013

The gallery of Oakland geological science

31 May 2013

OMCAserp

The Oakland Museum of California has finished its three-years-plus shutdown of the Natural Science gallery; the new Gallery of California Natural Sciences had its grand opening today. I got a backstage look at it earlier this week and gave it a thumbs-up for KQED Science yesterday. For me the highlight is the gateway section of the gallery, all about Oakland. All except for Oakland (and California) geology. As far as geology goes, the museum’s great serpentinite boulder on the roof, shown here in 2000, is still as good as it gets.

You’ll see in the new gallery how Oakland looked 300 years ago: its forests and grasslands and marshes. But you won’t see how it looked 30,000 years ago, or 3 million, or why those times are still relevant today. You won’t get a clue to the underlying framework that explains this landscape, or the deep history encoded there. You won’t see a hint of the active faults that shaped, and continue to shape, our region, nor will you see how they link us to California—how all of California is united—in a tight tectonic embrace. You won’t learn where and why the first Oaklanders dug for stone and gravel and water, or why they stopped. You’ll be able to add your backyard oak to a biome database that maps the ghostly living traces of our original forest—a marvelous thing!—but not your backyard outcrop or neighborhood roadcut.

All those things would have been simple to weave into the plan. The geologic subtheme would have enriched the whole exhibit and made it more truly a natural sciences gallery. Instead the new gallery is stuck, geologically speaking, back in 1969 when the old gallery was built. I’ll keep doing what I can here to fill the gap.

Oakland ochre

24 May 2013

oaklandochre

Here’s the story behind this photo. I just got back from five days in Fresno at the annual meeting of my regional section of the Geological Society of America, the Cordilleran Section. The first order of business was a field trip to see the Pleistocene fossils of the Fairmead Landfill, near Chowchilla. The guy whose hand this is is Blake Bufford, director of the Fossil Discovery Center just across the road from the site. His job is to follow around the giant scrapers at the landfill when they dig new pits and watch for fossils, so he’s the most important pair of eyes in the entire project. Blake showed our group the latest pit and then accompanied us to the Center for a tour and a reception by the FDC’s owners, the San Joaquin Valley Paleontology Foundation. Some nice Madera County wine, local cheese, “mammoth” meat balls and so on.

Blake and I got to talking, and the topic of Oakland came up. He asked if I knew anything about the traditional ochre diggings he had visited there. I told him about the Holy Names site, but that’s not the one he meant. No, he said, this was another place that was in the process of being wiped out to build a supermarket, where both red and yellow ochre were produced. “Let me show it to you.”

The Center is full of fossils, but it also has a little display cabinet dedicated to the people who once had the area to themselves, the Chowchilla tribe. There was an antique woven reed basket, of course, but everything else was a modern replica made with traditional techniques: arrows with interchangeable arrowheads, various kinds of twine, deerbone trowels and scrapers, a tiny wooden flute, necklaces, a soapstone bowl and trade beads, and balls of red and yellow ochre. Blake made all of it. He unlocked the case and showed me everything in it. He made the ochre balls, the size of a small egg, by grinding the stone to powder, then mixing it with boiled soaproot to hold it together. “We don’t know exactly what they used, but this worked.” There were a couple of raw ochre specimens lying next to them. “I collected this one from Oakland,” he said, and I said, “Please let me photograph that.”

Tuxedo terrace

12 May 2013

The Fan, my name for the lower hills in central Oakland, has a lot of subtle topography that I’m getting to know as I ramble over its contours. The little valleys are one feature I enjoy perceiving, but the places between them are interesting too. The San Antonio lobe of the Fan, between 14th Avenue and Fruitvale, has a flat top at about 200 feet elevation. This is in the Tuxedo neighborhood, looking down 21st Avenue toward the bay. 22nd and 23rd are the same way.

tuxedoterrace

There doesn’t seem to be a reason for such a flat stretch on an ordinary alluvial fan. Fans slope; that’s why they’re fans. I have to assume that the ground was not excavated flat but is naturally that way. Is it possible that this is a relict wave-cut platform, similar to the Clinton marine terrace but higher and older?

Arguing against that hypothesis, the height is problematic. On the other hand, the East Bay hills are rising and so may be the land west of the Hayward fault. It may be rising in fits and starts (meaning in episodes measured in thousands of years). The next thing I want, and have wanted for a long time, is a really accurate terrain map of Oakland. It would look like the standard digital elevation model of Oakland but would be compiled from lidar data and be accurate to a centimeter or so. Maybe my eyes are fooling me; after all the street does slope a little.

Montclair ballfield and the Hayward fault

4 May 2013

This is the view from atop the old railroad crossing at Mountain Boulevard, overlooking the south end of Montclair Playground.

montclairfield

The Hayward fault is mapped running through here from about third base on the ballfield at the left across the field of view. Two trenches were dug across the fault right here in 1981, and Jim Lienkaemper, the US Geological Survey’s (therefore the world’s) leading expert on active faults in Northern California, found evidence that the 1868 earthquake ruptured the fault here. Here’s part of the map he published in 1992 showing this area (at the REN in WARREN).

HFmontclair

The map is oriented so the fault runs vertically. The codes refer to evidence of active creep (C2) and vaguer evidence of creep (C3), geomorphic features of greater and lesser distinctness (G2, G3), and the trenches (T) I mentioned. “H2″ means there was good evidence of fault motion in the last 12,000 years—in this case, historic motion. The little oval at the WA in WARREN is a sag basin, now a water feature in the park. From top to bottom, the two-letter codes are as follows: gi, gradual inflection in slope; rw, right-offset wall; sl, linear scarp; jo, opened joints or cracks in concrete; sc, scissor point (where the up and down sides switch); rb, racking/distortion of building; as, arcuate scarp; dr, depression in a right stepover (sag basin); rc, right-offset curb; so, surveyed offset feature. The other codes refer to specific publications. This level of detail is available for the entire length of the fault, and while the USGS considers its online database of 2008 to be the most current, I like the format of this older map, Miscellaneous Field Studies Map MF-2196


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