Uranium minerals have been found at several localities in west Texas. In the King Mountain area in southwestern Upton County carnotite forms coatings along joint planes and in borings in marineCretaceous limestone. In the Hueco Mountains area in El Paso and Hudspeth counties carnotite and similar secondary uranium minerals form coatings in caliche and colluvium of Pleistocene ( ? ) or Recent age, and along joints and bedding planes in limestone of Permian age. No uranium ore has been produced, however, from either area.

Fall Prong quadrangle is in the marginal portion of the Edwards Plateau near the southeastern corner of the Llano region. Almost three-quarters of the quadrangle is within the Edwards Plateau, and the rest consists of valleys of the Llano basin cutting back into the plateau.