Radon in soil correlates directly with the bedrock geology in unglaciated terranes. In the Hylas shear zone, Virginia, the rock units exhibit a marked contrast in uranium concentration which is reflected in soil randon. The soils are clay-rich and are derived directly from the underlying bedrock. Even small geologic features such as pergmatite veins and thin shear zones are discernable by differences in soil radon concentrations. This bedrock/soil randon correlation is obscured in areas with thick glacial covers. The Reservoir fault area, New Jersey, is proximal to a terminal moraine. Although the bedrock units exhibit a strong contrast in radioactivity and uranium concentration, soil radon concentrations in the overlying tills reflect the local chemical and physical properties of the till rather than the bedrock. ¿ American Geophysical Union 1990