Virtually all rocks and soils contain uranium, which undergoes radioactive decay into hazardous radon gas. The average uranium concentration of crustal rocks is 2 to 3 parts per million (ppm). Geologic materials containing anomalously high levels of uranium (greater than 6 ppm) have greater potential for producing radon gas that can seep into homes and buildings and accumulate in hazardous concentrations. This map shows areas where uranium is know to be present in anomalously high concentrations and where there is a greater-than-average probability of homes having hazardous indoor-radon concentrations. Locations of uranium mineral districts and districts with byproduct uranium production or associated uranium mineralization were derived from Keith and others (1983). Granites with unusually high uranium concentrations include the Lawler Peak Granite north of Bagdad (Anderson and others, 1955; Silver and others, 1980), the Dells Granite norhteast of Prescott (Krieger, 1965; Silver and others, 1980; Proctor and others, this volume, p. 61-81), and two granitic plutons near Kingman (Loghry and Heinrichs, 1980). Locations of other areas with anomalously high uranium concentrations were derived from Scarborough (1981), Doorn and Pewe (1991), and studies presented in this bulletin. Scale 1:1,000,000