U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchivado el 29 de marzo de 2012 en Wayback Machine., accessed June 20, 2011
web.archive.org
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchivado el 29 de marzo de 2012 en Wayback Machine., accessed June 20, 2011