These maps are part of a folio of maps of the Ajo and Lukeville 1° x 2° quadrangles, Arizona, prepared under the Conterminous United States Mineral Assessment Program. Other publications in this folio include U.S. Geological Survey Miscellaneous Field Studies Maps MF-1834-A, 1834–B, and 1834–C and U.S. Geological Survey Open-File Reports 82–419, 82–599, and 83–734. Open-File Reports 82–419 and 83–734 constitute the basic data and initial interpretation on which this discussion is predicated. Open-File Report 82–599 is an aeromagnetic map.