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.
