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USGS Water Resources Maps and GIS Data
USGS GIS data of the United States water resources maps, soil, hydrology, and weather. Contains multiple links to useful and informative websites. -
New York State GIS Clearinghouse
Collection of links to various forms of spatial data for New York State and other areas; includes Digital Elevation Models, Digital Line Graphs, Geologic Maps, water/hydrology... -
Virginia Hydrologic Unit Explorer
Interactive GIS map of Virginia's hydrologic features.