Vein-type U deposits of geologic interest and commercial significance occur in the Cochetopa mining district. The U minerals in these deposits have been precipitated from hypogene solutions probably related to Tertiary igneous activity in the district. Silicification and brecciation of the sedimentary rocks in the Morrison formation and the Dakota sandstone, in and adjacent to fault zones, controlled deposition of U minerals from hydrothermal solutions. The most important deposits in the district are at the Gunnison Mining Company's Los Ochos claims where substantial reserves of ore in pipelike and in vertically tabular bodies have been blocked out. Pitchblende, the dominant U mineral, is associated with abundant clay and minor amounts of marcasite. As a result of studies carried out in the district, certain pertinent geologic criteria on ore localizing influences have been established.