This map shows the extent of the Edwards-Trinity aquifer system.  It is based on GIS data from the National Atlas of the United States at http://dds.cr.usgs.gov/pub/data/nationalatlas/aquifrp025.tar.gz.  The metadata provides, in part:
 Citation:
   Citation_Information:
     Originator: U.S. Geological Survey
     Publication_Date: 200310
     Title: 
       Principal Aquifers of the 48 Conterminous United States, Hawaii, Puerto 
       Rico, and the U.S. Virgin Islands 
     Edition: Version 1.0
     Publication_Information:
       Publication_Place: Madison, WI, USA
       Publisher: U.S. Geological Survey
     Online_Linkage: &lt;http://nationalatlas.gov/atlasftp.html&gt;
 Description:
   Abstract:
     This map layer contains the shallowest principal aquifers of the 
     conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin 
     Islands, portrayed as polygons.  The map layer was developed as part of 
     the effort to produce the maps published at 1:2,500,000 in the printed 
     series "Ground Water Atlas of the United States".  The published maps 
     contain base and cultural features not included in these data.  This is a 
     replacement for the July 1998 map layer called Principal Aquifers of the 
     48 Conterminous United States.
   Purpose:
     These data are intended for use in publications, at a scale of 1:2,500,000 
     or smaller.  Due to the small scale, the primary intended use is for 
     regional and national data display and analysis, rather than specific 
     local data analysis.

See the source data for the complete metadata.

This map uses the polyconic projection centered on the west 100th meridian: "+proj=poly +lon_0=100W"
Own work
Kbh3rd