Generalized boundaries of the National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 2001-2012

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 to be studied
during the second decade of the NAWQA Program, from 2001-2012
("cycle 2"). The coverage is intended only for drawing
ILLUSTRATIONS, NOT for spatial analysis.