Radon in California
While California may have, on average, a small percentage of houses expected to have elevated radon it has a huge population. Also there are areas of high radon potential located in densely populated areas of the state. As a result some urban areas may have large numbers of houses with elevated radon levels.
Radon Potential Maps
The Indoor Radon Abatement Act of 1988 directed the U.S. Environmental Protection Agency (USEPA) to identify areas of the United States that have the potential to produce elevated levels of radon. US EPA, along with U.S. Geological Survey (USGS) and the Association of American State Geologists, produced a series of maps and documents (EPA's Map of Radon Zones, CALIFORNIA 402-R-93-025). The full report is available upon request--contact CDPH's Radon Program.
The maps of Radon Zones identify areas of each state that have the highest potential for elevated indoor radon levels (greater than 4 pCi/L) (California map, U.S. map). The maps were designed to assist national, State and local governments and organizations to target their radon program activities and resources and should not be used to determine radon levels of a given area or house within a particular county.
Other Information
See Department's Indoor Air Quality Program's Sierra Radon Study.
For information on geology and radon, see