The Clatsop Plains are an area of wetlands and sand dunes between the Northern Oregon Coast Range and Pacific Ocean in northwestern Oregon in the United States. They stretch from near the mouth of the Columbia River south to the vicinity of Tillamook Head near Seaside. The plains are drained by several coastal rivers include the Skipanon River and Lewis and Clark River, which flow parallel to the coast and empty into the Columbia at Youngs Bay near Astoria. The plains are named for the Clatsop tribe of Native Americans who lived in the area at the time of the arrival of Europeans at turn of the 19th century.
These plains were developed from sand filling in the shoreline during the late Quaternary age.[1] The northern portion is a result of the creation of the south jetty on the Columbia River built in 1885.[1] Within the plain are several lakes including Cullaby, Smith, and Coffenbury which are filled by groundwater and not local streams or rivers.[1]
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