Abstract: Ten days were spent during June 1955, examining the sedimentary rocks along the San Juan and Colorado Rivers between Mexican Hat, Utah, and Lee's Ferry, Arizona. The most favorable area for uranium deposits occurs in the Shinarump member of the Chinle formation between Clay Hills Crossing and Spencer Camp along the San Juan River. Mineralization is spotty and deposits are small and almost all below ore-grade. Only one small mine, the Whirlwind, is currently producing ore. Gray-green alteration of the underlying Moenkopi is moderately developed in the vicinity of the Whirlwind mine; elsewhere alteration is weakly developed.

Introduction: Reconnaissance for uranium in central and southwestern Arkansas was carried out as a joint project of the U.S. Atomic energy Commission and the U.S. Geological Survey during March and May 1954. The project was planned as an investigation of several areas of known abnormal radioactivity, and as a search for others, by airborne and ground radiometric reconnaissance.