Is Los Angeles in a high radon zone?

Short answer: EPA’s Map of Radon Zones places Los Angeles County in Zone 2, which EPA describes as "Moderate potential; average indoor radon levels may be between 2 and 4 pCi/L." A zone describes the county, not your house: EPA says homes with elevated radon have been found in all three zones, and all homes should be tested.

What EPA’s map says about Los Angeles County

EPA’s radon zone data lists Los Angeles County, California as Zone 2. EPA’s legend for Zone 2: "Moderate potential; average indoor radon levels may be between 2 and 4 pCi/L."

EPA: "The Map of Radon Zones was developed in 1993 to identify areas of the U.S. with the potential for elevated indoor radon levels." Zones are assigned county by county, so every address in Los Angeles County gets the same EPA zone.

More local maps

EPA’s California map recommends that it "be supplemented with any available local data." For part of the county, the California Geological Survey published a Radon Potential Zone Map for Southern Los Angeles County (Special Report 182, 2005). That map states that "building-specific radon levels can only be determined by indoor radon testing."

Why a zone is not a test result

EPA: "The Map of Radon Zones should not be used to determine if individual homes need to be tested." "Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon."

EPA’s guidance on results: "Fix your home if your radon level is 4 picocuries per liter (pCi/L) ... or higher," and "Consider fixing if your level is between 2 and 4 pCi/L."

What Ground Report checks here, and what it doesn’t

The free score checks:

The EPA radon zone for the county of a street address, named as EPA’s Map of Radon Zones. Zones 1 and 2 show a finding with a recommendation to test.

It does not check:

The radon level inside your home. Ground Report does not measure radon, and no map can.
The California Geological Survey’s local radon potential maps. Ground Report uses EPA’s county zones only.

Get a free score for a street address

Sources

Sources last reviewed 2026-10-28. Quotes are taken from the linked pages. This page is general information, not a home inspection, a water test or an official flood determination.