Hydrologic units describe drainage areas used by the USBR. Hydrologic Units at 1:100,000 meter resolution. This coverage was generated using 250k resolution obtained over the Internet from the USGS mosaic site: <http://edcwww.cr.usgs.gov>
This coverage was then resampled by the IDS Group (CSU) using the Hydrology at 1:100,000 meter resolution (../hydro/hydro100) and Elevation Contours at 1:100,000 meter resolution (../topography/cont100m) coverages. New points were selected based on elevation and river features in Arc/Info.