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State overview

Radon in California

Of California's 58 counties and county equivalents, EPA places 2 in Zone 1, 29 in Zone 2, 27 in Zone 3. Zones are county-wide predictions; testing is the only way to know your home's level.

All 58 counties

CountyEPA zone
Alameda CountyZone 2
Alpine CountyZone 2
Amador CountyZone 2
Butte CountyZone 3
Calaveras CountyZone 2
Colusa CountyZone 3
Contra Costa CountyZone 2
Del Norte CountyZone 3
El Dorado CountyZone 2
Fresno CountyZone 2
Glenn CountyZone 3
Humboldt CountyZone 3
Imperial CountyZone 3
Inyo CountyZone 2
Kern CountyZone 2
Kings CountyZone 3
Lake CountyZone 3
Lassen CountyZone 3
Los Angeles CountyZone 2
Madera CountyZone 2
Marin CountyZone 3
Mariposa CountyZone 2
Mendocino CountyZone 3
Merced CountyZone 3
Modoc CountyZone 3
Mono CountyZone 2
Monterey CountyZone 2
Napa CountyZone 3
Nevada CountyZone 2
Orange CountyZone 3
Placer CountyZone 2
Plumas CountyZone 2
Riverside CountyZone 2
Sacramento CountyZone 3
San Benito CountyZone 2
San Bernardino CountyZone 2
San Diego CountyZone 3
San Francisco CountyZone 2
San Joaquin CountyZone 3
San Luis Obispo CountyZone 2
San Mateo CountyZone 2
Santa Barbara CountyZone 1
Santa Clara CountyZone 2
Santa Cruz CountyZone 2
Shasta CountyZone 3
Sierra CountyZone 2
Siskiyou CountyZone 3
Solano CountyZone 3
Sonoma CountyZone 3
Stanislaus CountyZone 3
Sutter CountyZone 3
Tehama CountyZone 3
Trinity CountyZone 3
Tulare CountyZone 2
Tuolumne CountyZone 2
Ventura CountyZone 1
Yolo CountyZone 3
Yuba CountyZone 2

Source: EPA radon zones spreadsheet (EPA 402/A-16/001).