The Stanley uranium district in central Idaho produced a modest amount of uranium ore from 1957 to 1962. The average grade (about 0.18 percent U₃O₈) of the uranium deposits mined in the district was comparable to that of other U.S. producers, but its output (no more than 8,000 tons of uranium ore per year) and its mines were relatively small. The uranium deposits are found as disseminated minerals with strata-bound deposits of fluvial sedimentary rock and as pockets in silicified fractures cutting granitoid batholithic rocks. A notable finding of the reconnaissance geochemical study was the high arsenic content of the strata-bound deposits, which was evident in rock, mine-waste, and water samples. In contrast, arsenic content of rock and mine-waste samples from the vein-type deposits was much lower. None of the spring or stream water sampled away from mine sites contained arsenic or other metal concentrations above the EPA proposed drinking water standards.