Digital Data Sets Describing Principal Aquifers, Surficial Geology, and Ground-Water Regions of the Conterminous United States

This report contains digital data sets describing principal aquifers, surficial
geology, and ground-water regions of the conterminous United States. The data
source for the principal aquifers and surficial geology data sets is "The
National Atlas of the United States of America" (U.S. Geological Survey, 1970;
Hunt, 1979). The data source for the ground-water regions data set is
"Ground-Water Regions of the United States" by Heath (1984). Some of the
digital lines describing coastlines were modified from U.S. Geological Survey
boundary information (U.S. Geological Survey, 1990; Lanfear, 1984). Because
most of the source materials do not cover Alaska and Hawaii, only the
conterminous 48 states are included in these data sets.

Compilation of the data sets was supported by the National Water-Quality
Assessment (NAWQA) Program of the U.S. Geological Survey (USGS). The objectives
of the NAWQA Program are to: (1) describe current water-quality conditions for
a large part of the Nation's freshwater streams, rivers, and aquifers, (2)
describe how water quality is changing over time, and (3) improve the
understanding of the primary natural and anthropogenic factors that affect
water-quality conditions. National analysis of data, based on aggregation of
comparable information obtained from across the United States, is a major
component of the NAWQA Program. The data sets included in this report were
created in support of NAWQA national data analysis activities.

[Summary provided by the USGS.]