Friday, March 1, 2013

The Joy of Roadcuts: A Few Friday Mystery Photos

Photo by Mrs. Geotripper
Rocks are easy to find in California. In places like Death Valley and the Mojave Desert, and in the high peaks of the Sierra Nevada and White Mountains, the rock exposures are fresh and quite easily observed. One could get pretty spoiled out here in comparison to those who live in much of the eastern United States or lowland Europe. In more humid environments, practically the only rock exposures not covered by green overburden and soil are in deep river canyons, or in road cuts.
Photo by Mrs. Geotripper

In the Sierra Nevada foothills, there are lots of rock exposures of the Western Sierra Metamorphic Belt, but they tend to be deeply weathered and a lot fine details are not easy to see. Without the road cuts, a lot of interesting things would not be visible. Last weekend, I had a chance to go fossil hunting in the late Jurassic rocks of the Mariposa formation, and as I noted in a recent post, we found ammonites, pelecypods, belemnites, and even a sprig of redwood.

We also found some enigmatic stuff in the road cuts that kind of defied identification. The odd features are shown below, and I've downloaded them at full resolution so you can take a closer look (click on the photos)
The Mariposa formation in which these things occur is a marine deposit consisting of shale, tuff, graywacke sandstone and occasional conglomerates that formed in a deep basin adjacent to volcanic arcs and the western edge of the North American craton.
So what do you think?

1 comment:

Anonymous said...

Good pictures - though for a minute you were in El Dorado Co. where a group of us from work went on a 3-hour tour of asbestos zones. Similar roadcut emphasis. Are those straight lines fossils of the cut-making machinery opening small windows into the next layer?