U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchivado el 29 de marzo de 2012 en Wayback Machine., accessed March 21, 2011
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchivado el 29 de marzo de 2012 en Wayback Machine., accessed March 21, 2011