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USGS releases map of known California asbestos deposits

California’s state rock is serpentine, and guess what? It contains asbestos!

This week, the U.S. Geological Survey (USGS) released a comprehensive map of all places in California where asbestos occurs, including mines and natural outcroppings of asbestos-containing minerals.

One of the things about California that surprised me after I moved here is that the Clear Creek Management Area in San Benito and Fresno counties, has been known as the largest U.S. deposit of asbestos, which is a natural mineral and a known carcinogen in humans. Clear Creek contains white asbestos in the form of the mineral chrysotile. Another thing that surprised me is that Clear Creek has 35,000 visitors each year and that the Environmnetal Protection Agency found that dangerous levels of asbestos dust are raised by motorcycles and other off-road vehicles in Clear Creek.

In 2008 (I moved to California in 1990), a 31-square-mile portion of the off-road area was closed to visitors after a report suggested that long-term use of the area (five visits each year over 30 years) could be hazardous to human health. Any human use of the area, even hiking and camping, is believed to be potentially dangerous, especially for children, and has been outlawed while the Bureau of Land Management (BLM) completes an new management plan and environmental impact statement.

Earlier studies, over several decades, found high levels of asbestos in the the area. You might find it incongruous that a state like California that pretends to be so “environmentally correct” would allow off-road vehicles through an area for which the use of industrial-grade respirators has been recommended. I know that I did – especially when the State Legislature of California uses environmental toxicity as an excuse for other things that it wants to do, like banning lead ammunition. Clear Creek even has an EPA-designated toxic superfund site, the former Atlas asbestos mine.

Some people do not believe that asbestos dust is particularly harmful. As I have said before, that’s OK, because science does not care WHAT you believe – science just examines what IS! To skeptics, I would recommend the study of Libby, Montana, the hometown of a friend of mine, in which hundreds of people are sick or dying (or dead) from asbestos exposure in their occupations in mining. Libby, Montana is ALSO the name of a 2004 documentary film about the largest community-wide exposure of people to a toxic substance in U.S. history, which was shown on PBS.

Last year, I wrote a bit about the Clear Creek Management Area (several of the BLM pages I cited no longer exist as the result of the re-evaluation) in an earlier blog entry entitled “Toxic Trails, to you….” in which I also discussed harmful heavy metal contamination of hiking trails in “Gold Country” that were the subject of a Sierra Fund study.

The USGS map also shows major asbestos outcropping in Shasta, Trinity, Siskiyou and Del Norte counties, as well as amaller outcrops along the coastal ranges and the Sierra Nevada.

-Bill at

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