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 first decade of the NAWQA Program, from 1991-2001 ("cycle 1"). The coverage is intended only for drawing ILLUSTRATIONS, NOT for spatial analysis. The sources of this coverage were the full resolution NAWQA study unit coverage, which is available at http://water.usgs.gov/lookup/getspatial?nawqacyc1 and the coastline from a 1:2 million county coverage generalized for display at the scale of 1:34 million.
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USGS Unnumbered Series
Generalized boundaries of the National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 1991-2001