This study concerns the distribution, geologic character, probable extent, and potential economic importance of those various mineral substances that have been found to occur within the Gila River Indian Reservation in Arizona. Information regarding these items was obtained by means of geologic examination and mapping, supplemented by laboratory tests and analyses, during a period which extended from April 17 to August 18, 1963. The report offers suggestions for future prospecting and field exploration, but it does not attempt to give quantitative (tonnage) estimates of the occurrences of economic materials or the total value for any of the mineral deposits.