Archive for May, 2009

Prairie serpentinites

22 May 2009

Here’s an assortment of serpentinite from the Serpentine Prairie. The first three show the polished surfaces that form so easily on this soft rock type, as well as the variety of blue-green colors. Remember, serpentinite is a metamorphic version of peridotite, the deep-seated, low-silica rock that forms the upper mantle and the bottom of oceanic plates.

serpentine prairie

serpentine prairie

serpentine prairie

Darker bits may reflect more iron-rich protoliths, or maybe rocks that are less altered.

serpentine prairie

serpentine prairie

And remember, no collecting in the park. If you like serpentinite, do what I did and collect from the roadside just to the west of the park, or down in the Crestmont neighborhood.

serpentine prairie

Learn more about serpentinite on my site.


Serpentine Prairie

18 May 2009

serpentine prairie

Serpentine Prairie is a segment of Redwood Regional Park right across Skyline Boulevard from the Crestmont neighborhood (where my very first post came from). It’s a small remnant of a serpentine barren, most of which is occupied by hilltop homes. This is the entrance from the parking lot at 11500 Skyline Blvd. Some large boulders of serpentinite are here to keep out vehicles, but they’re handy for studying this rock type. The lush greenery is foxtail grass, an alien invader that benefits from the nitrogen of dog urine near the path and the absence of fire.

serpentine prairie

This view shows how serpentine ground differs from sandstone slopes in the distance. Serpentinite yields a soil that is very high in iron and very low in calcium, phosphorus and nitrogen; it also includes high levels of chromium, nickel and cobalt that are toxic to most plants. The stony slope in the left distance is a true serpentine barren, with almost nothing growing on it. The near ground has many endemic grasses and flowers but also a lot of foreign plants. Now is the time to see it. I visited on May 15 and caught the endangered Presidio clarkia in bloom (see it on my fotothing site).

serpentine prairie

The serpentinite itself presents a variety of colors from brown to grass-green, but the bulk of it here is close to bluejean color, hard to capture on camera but quite striking in person. Here it is: California’s state rock with Eschscholtzia californica, the state flower.

Visit the prairie now, but respectfully: this fall the park plans to fence off 3 acres of the land and start protecting it from degradation. If you walk amid the fields, watch your step and pretend that you’re inside that fence. Of course, there is no picking the plants or collecting the rocks. There’s plenty of serpentinite that’s just as good along the roadside on Skyline.

Teach your children rocks

10 May 2009

teach geology

Eldridge Moores is a grand old man of California geology, and indeed of American geology. That’s him talking about structural geology with his arms, at the intersection of Tunnel Road and Caldecott Lane in early May 2005. He played Virgil to John McPhee’s Dante in Assembling California. Lately Eldridge has been pushing the State of California to do something very simple and obvious: recognize high-school geology as a subject satisfying the lab requirement for California college admission.

It’s obvious because geology is an applied version of every other science: rocks are chemicals, geologic processes follow the laws of physics, fossils are a branch of biology. Indeed, every lab science originated in practical problems with the world around us. The world is still there, and geologists are its intimates.

It’s simple because we have a national and state consensus around supporting science, especially environmental science, with strong leadership from President Obama and Governor Schwarzenegger. Eldridge has lobbied every year for adding Earth science to the lab science requirement. This year both the National Association of Geoscience Teachers and the National Earth Science Teacher Association are joining his efforts, and so am I, and I would love it if you did too.

It’s important because you may notice that only one person in this photo was younger than 25. Somewhere between the age when we’re all dinosaur fanatics and adulthood, geology seems to get lost. Part of fixing that is giving high schools a bit more incentive to offer Earth science courses.

The procedure is to write a letter (email or paper) to the UC Academic Council, which is right here in Oakland, and other UC officials. They are laying groundwork for the next set of curriculum guidelines for high schools, and time is critical. The call to action, talking points and a sample letter are all posted by “Geotripper” Garry Hayes on the NAGT Far West Section blog. Garry puts it well here: “Earth Science has always taken a back seat to chemistry and physics, and yet is most vivid example of chemistry and physics at work in the real world. We need to support the teaching of the earth sciences at the secondary level.”

Rockridge rocks

4 May 2009

rockridge quarry

Rockridge got its name from its outcrops. Although the location of the original Rock Ridge is not quite clear, the Bilger quarry, now home to the Rockridge Shopping Center, exposes some of the bedrock of Rockridge. This is the Franciscan sandstone that makes up the western end of the quarry. I think it was probably considered overburden, something to be removed or maybe used for cheap landfill. There was surely a big demand for cheap fill as Oakland and the other Bay cities encroached into the wetlands. The eastern end, where the pond is today, yielded a higher grade of traprock, a light-colored fine-grained diorite that weathers with rusty stains. There are boulders of it all over the neighborhood; a good specimen is in front of the Quarry Ridge Apartments in the first block of Gilbert Street, built next to where the rail line from the quarry once ran.

rockridge serpentine

In between the two rock types is a fracture zone with a lot of this black, greasy-looking stuff. Grinding along the fault zone and deep-seated alteration has turned the dark minerals into serpentine. That’s roughly where the broken wall is that I showed in the previous post.