See the base at the Vermilion Cliffs

The Chinle Formation is composed of the Shinarump, the Lower and Upper Petrified Forest, and the Owl Rock Members. The Shinarump is a basal conglomerate, made up of Paleozoic clastic and igneous cobbles. The Petrified Forest Member is composed primarily of alluvial shales and siltstones (Harris, 1977). The colors of the Painted Desert are created by iron and manganese oxides contained in the Chinle Formation. The Pliocene Bidahochi Formation may be found on some mesa tops in the Painted Desert (National Park Service, 1991).

Uranium is found in sandstone deposits in both the Chinle and Moenkopi formations. In typical sandstone type uranium deposits, the uranium is emplaced by groundwater solutions with their origins in igneous rock or volcanic ash. Because a reducing environment is necessary for the precipitation of uranium-bearing minerals, it often occurs in the presence of organic material or iron sulfides (Christensen, 1979) such as the buried trees, ferns and fauna of the Petrified Forest Member. Source National Park Service