Base map layers (hydrology, coastline, county and state boundaries)
from the digital National Atlas of United States, scale 1:2,000,000: 
!FNT93714;http://www-atlas.usgs.gov/atlasftp.html
!FNT93713;Lambert azumithal projection, center of projection 100 west, 45 north.
Shaded-relief base map made by Joseph Colgan in ARC/INFO, using
NOAA 30 arc-second digital elevation data available online at:
!FNT93714;http://www.ngdc.noaa.gov:80/seg/fliers/se-1104.html