This report, prepared in cooperation with the City of Austin, delineates the outcrop of the Edwards aquifer that is hydrologically associated with Barton Springs. The Edwards is a regional aquifer system in central Texas that extends in a narrow belt from Kinney County to Bell County (index map) and lies within an area locally known as the Balcones fault zone. Hydrologic boundaries separate the Edwards auifer into several parts. Barton Springs is the major discharge point of the part of the Edwards aquifer in the Austin area (southern Travis and northern Hays Counties).