U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchiviato il 29 marzo 2012 in Internet Archive., accessed May 13, 2011
web.archive.org
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchiviato il 29 marzo 2012 in Internet Archive., accessed May 13, 2011