Abstract: Most of the uranium deposits in the Uravan and Gateway mining districts are in the persistent upper sandstone stratum of the Salt Wash member of the Morrison formation. Areas in which this stratum is predominantly lenticular have been differentiated from areas in which the stratum is predominantly nonlenticular. The most favorable ground for uranium deposits is in areas of lenticular sandstone where the stratum is underlain by continuous altered greenish-gray mudstone. Ore is localized in scour-and-fill sandstone beds within favorable areas of lenticular sandstone. Regional control of the movement of ore-bearing solutions in the principal ore-bearing sandstone zone is indicated by belts of discontinuously altered mudstone transitional in a northerly and southerly direction from an area of unaltered mudstone to areas of continuously altered mudstone ; and an area of unaltered mudstone in which no ore deposits are found and an increase in size, number, and grade of ore deposits from areas of discontinuously altered to continuously altered mudstone. Discrete regional patterns of ore deposits and altered mudstone are associated with Tertiary structures; where these structures and favorable host rocks occur in juxtaposition, regional controls appear to have localized ore deposits.