US States with the Highest Radon Levels

Radon is, under standard conditions, gaseous and easily inhaled, and therefore a health hazard. It is often the single largest contributor to an individual's background radiation dose, but due to local differences in geology, the level of exposure to radon gas differs from place to place. A common source is uranium-containing minerals in the ground, and therefore it accumulates in subterranean areas such as basements. Radon can also occur in some groundwater like spring waters and hot springs. Climate change may cause radon previously trapped underground to be released as permafrost thaws. It is possible to test for radon and use techniques such as sub slab depressurization for mitigation. Which states have the highest average radon levels?