Aerial gamma-ray data were compiled to produce a map showing the distribution of radium (226Ra) in near-surface materials in the Pacific Northwest (Washington, Oregon, and Idaho, and parts of Montana, Wyoming, California, Nevada, and Utah). A comparison of measurements of indoor concentration levels of randon (222Rn) in homes with the apparent surface concentration of radium shows that aerial gamma-ray data provide a first order estimate of the relative amounts of indoor radon for township-sized areas where soils have low to moderate permeability. Townships with average indoor randon levels above the general trend of the data are almost all characterized by soils that have higher intrinsic permeabilities. ¿ American Geophyscial Union 1990