Radon Pros in California

Last updated: March 2026

California's radon risk is often underestimated because the state is not traditionally associated with radon concerns. However, EPA mapping shows a mix of all three risk zones across the state. The northern Sierra Nevada foothills, parts of the Central Valley, and some southern inland areas are classified as Zone 1. Coastal regions are mostly Zone 2 to Zone 3 with lower average readings. The granite-rich Sierra Nevada foothills produce elevated radon levels driven by the same uranium-bearing geology that affects mountain states. Areas near active and inactive fault lines can also show elevated readings due to increased soil permeability. California does not require state-specific radon certification, relying on national NRPP and NRSB credentials as the standard. In real estate transactions, radon testing is not commonly requested in most California markets, which contributes to lower public awareness. What makes California's situation unique is the combination of underestimation and genuine risk — homeowners in the foothills, Central Valley, and parts of Santa Barbara and Ventura counties may have elevated indoor radon without realizing it. The California Department of Public Health recommends testing, particularly for homes with ground contact in Zone 1 and Zone 2 areas. Given California's diverse geology, county-level EPA zone maps are especially important for identifying local risk.