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~,~ i '""\,.' BUREAU OF ~'1INES GEOLOGY The Ruin Canyon Dam and Reservoir sites are located on the outcrop of the Dakota formation (fig. 5). A buff sandstone member, 10 to 20 feet thick, is exposed by erosion in the lover part of the canyon at the dam axis. This member is below the surface in the reservoir area. From the gentle slope of the hillsides and limited sandstone float, it is inferred that most of the section above, the prominent sandstone is composed of shales or silty shales. TIJere may be thin subbituminous coal seams, but if they exist, they are likely to be thin, very local, and simil~r to those seen farther north and east. An aeolian deposit of red-brown sandy clay covering most of the res- ervoir area is the farm soil of the basin. It is estimated by Bureau of Reclamation personnel to range in thickness from a few inches to 10 feet. The averaee thickness is estimated to be 4 to 5 feet. llINERAL PJlSOURCES Sodium Chloride Sodium chloride deposits can be expected in the Paradox formation at a depth of 6,300 feet. AlthouFh a considerable salt thickness is likely, depth, 101' unit salt value, and size of Imo,m near-surface reserves vir- tually nullify any present value this reserve might have. Uranium Both the ShinarU1llP and Chinle formations underlie this e,rea. These formations have yielded considerable uraniu~m in areas to the west and northwest, althouV1 the nearest known deposits, in the Dolores Canyon to the north, were ~uite disappointing. As these formations occur in the interval from 1,900 to 2,500 feet below the surface, and any exploration would have to be by blind drilling, the lildihood of finding e. commercial deposit under the reservoir site is quite remote. " ,..; : ~"} The ~~orrison formation also lmderlies the reservoir area. The Salt \'Iash member of the l>'lorrison formation contains exte~sive deposits of uranium to the north while minor deposits have been developed several mi.les to the west. Imy exploration in the reservoir area tlould have to be by blind drilling to a depth of 800 feet in a potentially unfavora.ble area. It is unlil<ely that uranium will be found in the r,lorrison forma~ tion Qnder the proposed dam and reservoir, althou~h such reserves are possible. I , I ,I , "'I I Cc-:~l , j The Dakota formation exposed at the surface may contain thin lenses of subbituminous coal. Although no such zones were seen in the dem or reservoir area, thin noncommercial coel seams are co~mon nearby. 88