What EPA's radon map says about Mendocino County

EPA places Mendocino County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Rank it against the rest of the country and Mendocino County lands in the 26th percentile for radon potential.

Mendocino County by the numbers

About 89,175 people live in Mendocino County, California, spread over 3,506.807 square miles. That works out to roughly 25 people per square mile. Among counties sharing Mendocino County's EPA zone, it outranks 78% of them by population. Geologically, Mendocino County is grouped into EPA Region 9 alongside 94 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Mendocino County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like Mendocino County testing above the action level often enough that skipping a test isn't the safe assumption.

Testing and mitigation in Mendocino County

Mitigation cost doesn't depend on Mendocino County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find California's state radon program

Mendocino County's test kit answers today; a Airthings radon monitor keeps answering for Mendocino County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Mendocino County carries, the zone explainer covers what it does and doesn't tell you about any one house.