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usgs.gov
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"Get Maps". USGS Topoview. US Geological Survey. Retrieved 21 June 2021.
"Get Maps". USGS Topoview. US Geological Survey. Retrieved 21 June 2021.
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012-03-29 at the Wayback Machine, accessed April 1, 2011