This study provides geological background information necessary for an evaluation of the earthquake hazard in an area of induced seismic activity at Monticello Reservoir, South Carolina. This region contains a thick stratified sequence of Proterozoic Z and Cambrian metasedimentary and metavolcanic rocks. In the early to middle Paleozoic, this sequence was recrystallized and deformed under metamorphic conditions that ranged from greenschist to amphibolite facies and experienced at least two episodes of folding. The region has been intruded by late kinematic to postkinematic granitoid plutons of Silurian and Carboniferous ages and by numerous northwest trending diabase diks of Late Traissic and Early Jurassic age. The region south of Monticello Reservoir in the Carolina slate belt experienced two episodes of faulting in the late Paleozoic and/or early to middle Mesozoic. The older group of faults trends approximately east, has only small displacements, and is characterized by extensive silicifiction of the fault zones. The younger group of faults trends approximately north has experienced dip slip displacements up to 1700 m and is characterized by carbonate mineralization in the fault zones. Both sets of faults are cut by an undeformed diabase dike of Late Triassic or Early Jurassic age. The induced seismic activity around Monticello Reservoir is occurring in a heterogeneous quartz monzonite pluton of Carboniferous age. Although laterally extensive faults have not been found in the vicinity of the reservoir, the pluton contains large enclaves of country rock and is cut by numerous, diversely oriented small faults and joint. These local inhomogeneities in the pluton together with an irregular stress field are interpreted to control the diffuse seismic activity around the reservoir. In view of the apparent absence of lengthy faults it is unlikely that a large-magnitude earthquake will occur in response to the stress and pore pressure changes related to the impoundment of Monticello Reservoir.