Generalized boundaries of the National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 1991-2001
This is a GENERALIZED version of the boundaries and codes used
for the U.S. Geological Survey's National Water-Quality
Assessment (NAWQA) Program Study-Unit investigations in the
conterminous United States, excluding the High Plains Regional
Ground-Water Study.  The data set represents the areas studied
during the …