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 About.com 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.


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