Over millennia, glaciers and beaver, in large part, constructed the drainage system of North America. Ruedemann and Schoonmaker (1938), both geomorphologists, advanced this seminal idea based on their studies of streams in the Adirondack Mountains. The two scientists observed that the floodplains were stair-stepped-rather than gradually sloped along the stream. Realizing that this pattern would result when beaver dams trap sediment, they concluded that glaciers gouged the river valleys out and that beaver filled them up.
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