Relationships between geology and uranium series element concentrations in stream sediments in north central South Carolina have important tectonic and environmental implications for the eastern Inner Piedmont, the Carolina terrane (a Late Proterozoic subduction-related volcanic island arc) and the Upper Atlantic Coastal Plain. Overlays of geologic maps and rose diagram plots of the National Uranium Resource Evaluation (NURE) stream sediment data for the Spartanburg and Lancaster 1º quadrangles, South Carolina and North Carolina, reveals that anomalously high levels of uranium and thorium (over 361 and 1978 ppm respectively) are present in stream sediments derived from the gneisses and 450 to 350 Ma metagranites in the Inner Piedmont, from the 400 and 300 Ma metagranites and granites in the Carolina terrane, and from the Cretaceous and Lower Tertiary sediments of the Upper Coastal Plain. In contrast, anomalously low levels (less than 0.5 ppm) of uranium and thorium are present in stream sediments derived from the Late Proterozoic metavolcanic-metasedimentary sequence and Late Proterozoic to Early Cambrian metagranites in the Carolina terrane. These same relationships are readily apparent in overlays of the geologic and aeroradiometric maps of the Spartanburg and Lancaster quadrangles. These relationships suggest: (1) the Carolina terrane came into contact with uranium-thorium-bearing continental margin sediments when it docked with North America (possibly during the Middle Ordovician) and that Middle Paleozoic accretion and Late Paleozoic overthrusting of the Carolina terrane and Inner Piedmont further onto North America generated granitic magmas by partial melting and assimilation of those uranium-thorium-bearing sediments; (2) that unless precautions and preventive measures are taken by individuals living in rural areas of the eastern Inner Piedmont and Upper Coastal Plain and on the 400 and 300 Ma metagranites and granites of the Carolina terrane, they will be exposed to hazardous levels of radon in their homes and to hazardous levels of uranium and thorium in drinking water from their wells.