This report is a compilation of the existing hydrogeologic data for Aberdeen Proving Ground, Aberdeen Area (APG-AA). Using boring data, the top of the metamorphic bedrock, top of the Cretaceous sediments, and three Quaternary terraces have been mapped. Geologic cross sections of the western half of the APG-AA peninsula, showing the relationship between the bedrock Cretaceous, and Quaternary units, have been constructed. The similar lithologies of the interbedded Lower Cretaceous Patapsco, Arundel, and Paxtuxent formations did not allow them to be mapped as separate units. Boring data from the Western Boundary Area study provided lithologic data to map the extent of the two oldest Quaternary terraces, Qt2 and Qt3. There was not sufficient data to accurately map the youngest Quaternary terrace, Qtl. Permeable aquifer zones in the Cretaceous units were identified in borings; however, available data did not allow them to be correlated over any appreciable distance on APG-AA. The Qt3 is a highly permeable water table aquifer. Water level data indicate that groundwater is moving vertically from the water table aquifer into the lower aquifer zones; however, the lower aquifer zones do not appear to be vertically or laterally well connected.