What EPA's radon map says about Siskiyou County

EPA places Siskiyou 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. That puts Siskiyou County in the 21st percentile nationally for radon potential — higher than 21% of the counties EPA has rated.

Where Siskiyou County sits nationally

About 42,498 people live in Siskiyou County, California, spread over 6,278.767 square miles. That works out to roughly 7 people per square mile. Among counties sharing Siskiyou County's EPA zone, it outranks 63% of them by population. Siskiyou County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Siskiyou 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. Even at Zone 3, Siskiyou County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

If Siskiyou County tests above the action level

Mitigation cost doesn't depend on Siskiyou 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

Siskiyou County's test kit answers today; a Airthings radon monitor keeps answering for Siskiyou 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.