Horseshoe and Bartlett Dams are located In the Transition Zone of central Arizona. Within this province, faults with evidence of Quaternary activity are widely scattered, and selsmiclty Is low In comparison to other parts of the western United States. However, most of the known or suspected Quaternary faults and most of the historic selsmlclty In Arizona occur within or adjacent to the Transition Zone. Based on data gathered during this study for Horseshoe and Bartlett Dams and on the results of previous studies for Stewart Mountain and Theodore Roosevelt Dams (Anderson and others, 1986; 1987), two recurrent Quaternary faults have been Identified In the Immediate area of the subject dams (within approximately a 50-km radius). The two faults are the Horseshoe and Sugar1oaf faults.