Abstract Uranium in the Marysvale volcanic field is known to occur in several geologic environments and is thought to occur in others. These known and hypothetical occurrences are of various kinds, ranging in derivation from rhyolite magma, through porphyry-type deposits, hydrothermal vein deposits, dispersed hydrothermal deposits, and, after secondary transport in ground and surface water, roll–front or sedimentary–trap deposits in basin-fill sediments. To date, only the hydrothermal vein environment has been productive, but billions of pounds of uranium were available in all other environments, and if proper conditions existed, significant concentrations probably formed by other processes. The intracaldera fill of the Mount Belknap caldera and sediment-filled basins adjoining the Tushar Mountains are especially favorable exploration targets for the undiscovered uranium believed to exist.