U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArkiveret 29. marts 2012 hos Wayback Machine. Hentet 19. maj 2011
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArkiveret 29. marts 2012 hos Wayback Machine. Hentet 19. maj 2011