From the site: "This geology shapefile covers the entire Susquehanna River Basin (2006 boundary). It represents the merging of three state (NY, PA, MD) bedrock geology spatial datasets in order to provide basic rock types of the Susquehanna River Basin. The dominant formation lithology that appears in the attribute table were grouped into 19 general rock types, such as sandstone, shale, schist, limestone, dolomite, etc. These rock types are also categorized by hydrostratigraphic terrain. The hydrostratigraphic terrain helps to identify the way in which water flows over or through these rocks."