U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012-03-29 at the Wayback Machine, accessed March 30, 2011
web.archive.org
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012-03-29 at the Wayback Machine, accessed March 30, 2011