Radon zones in California
| Butte County | California | 3 |
| Colusa County | California | 3 |
| El Dorado County | California | 2 |
| Fresno County | California | 2 |
| Glenn County | California | 3 |
| Humboldt County | California | 3 |
| Imperial County | California | 3 |
| Inyo County | California | 2 |
| Kern County | California | 2 |
| Kings County | California | 3 |
| Lake County | California | 3 |
| Lassen County | California | 3 |
| Los Angeles County | California | 2 |
| Madera County | California | 2 |
| Mendocino County | California | 3 |
| Merced County | California | 3 |
| Modoc County | California | 3 |
| Mono County | California | 2 |
| Monterey County | California | 2 |
| Napa County | California | 3 |
| Nevada County | California | 2 |
| Placer County | California | 2 |
| Plumas County | California | 2 |
| Riverside County | California | 2 |
| San Bernardino County | California | 2 |
| San Diego County | California | 3 |
| Santa Barbara County | California | 1 |
| Santa Clara County | California | 2 |
| Shasta County | California | 3 |
| Siskiyou County | California | 3 |
| Sonoma County | California | 3 |
| Stanislaus County | California | 3 |
| Sutter County | California | 3 |
| Tehama County | California | 3 |
| Trinity County | California | 3 |
| Tulare County | California | 2 |
| Yolo County | California | 3 |
Sources
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- California: EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
- EPA Map of Radon Zones, US Environmental Protection Agency, checked 1 November 2026
"Secondary" marks a source used only because the official page could not be read.