The mapping of geologic materials and a detailed stratigraphic understanding of geologic units are important for resource protection and evaluation of the Edwards and Trinity aquifers. The District partnered with the United States Geological Survey (USGS) to produce a hydrogeologic map of the Barton Springs Segment of the Edwards Aquifer in 1996. The District and the City of Austin continue to maintain and refine this map as new information becomes available. In 2004, a new geologic mapping provided the basis for refining the recharge zone of the Edwards Aquifer, which ultimately resulted in the ability to provide more aquifer protection.