California asbestos deposits mapped

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Asbestos is in our state rock, and it’s in more places than you might think.

The U.S. Geological Survey this week released a comprehensive map of all the known places in California where asbestos is found, including mines and exposed natural formations.

Off-roaders in the Clear Creek Management Area, in San Benito and Fresno counties, are all too familiar with white asbestos in the form of the mineral chrysotile. A 31-square-mile swath of the off-road vehicle area was closed in 2008 after a report suggested that extensive long-time use of the area (five visits a year over 30 years) could be hazardous to your health.

The federal Bureau of Land Management, which oversees the land, has kept most of the area closed to the public while it completes a new management plan and environmental impact statement.

The Environmental Protection Agency found that dangerous levels of asbestos dust were being stirred up by motorcycles and other off-road vehicles. Any human use, even camping and hiking, was deemed potentially dangerous, especially to children, and outlawed until the BLM develops a new plan for the area.

Clear Creek, which registers 35,000 visits a year, has long been known as the largest U.S. deposit of asbestos, a natural mineral and known human carcinogen. The area harbors an EPA-designated toxic Superfund site, the former Atlas asbestos mine. Previous studies over several decades found high levels of asbestos in the area.

Other hotspots for asbestos are in outcrops in the state’s far north: Shasta, Trinity, Siskiyou and Del Norte counties. It also surfaces along the coastal ranges and Sierra Nevada.

The map is part of an effort by the federal agency to identify locations nationwide where asbestos mineralization occurs.

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--Geoff Mohan