U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012년 3월 29일 - 웨이백 머신, accessed April 1, 2011
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U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012년 3월 29일 - 웨이백 머신, accessed April 1, 2011