The Missouri National Recreational River is a National Recreational River located on the border between Nebraska and South Dakota. The designation was first applied in 1978 to a 59-mile section of the Missouri River between Gavins Point Dam and Ponca State Park. In 1991, an additional 39-mile section between Fort Randall Dam and Niobrara, Nebraska, was added to the designation. These two stretches of the Missouri River are the only parts of the river between Montana and the mouth of the Missouri that remain undammed or unchannelized. The last 20 miles of the Niobrara River and 6 miles of Verdigre Creek were also added in 1991. The Missouri National Recreational River is managed by the National Park Service, with headquarters located in Yankton, South Dakota. Visitor centers are located at Ponca State Park, Niobrara State Park and the Lewis and Clark Visitor Center at Gavins Point Dam, overlooking Lewis and Clark Lake. It lies in parts of Boyd, Cedar, Dixon, and Knox counties in Nebraska, and Bon Homme, Charles Mix, Clay, Union, and Yankton counties in South Dakota. History People have lived along the river for some 10,000 years. Archeologists have found their tools and weapons, homes, foods, religious, and ceremonial objects. The River is one of three historic east-west corridors, similar to the Oregon and Santa Fe trails. It was a pathway of American Indians, Lewis and Clark, trappers and traders, steamboat captains, and settlers. French and Spanish traders preceded Lewis & Clark's 1804 expedition. The Yellow Stone was the first steamboat to sail this stretch of the river in 1832 on the way to Fort Union Trading Post. The 1858 Treaty with the Yankton Sioux opened the southeastern portion of the Dakota Territory to white settlement. The Homestead Act of 1862 encouraged immigration into the region. During steamboat era, the Missouri was characterized by shifting channels, numerous braided channels, chutes, sloughs, islands, sandbars, and backwater areas. Well over 300 steamboats sank in the river between 1819 and 1920. By the mid-20th century, extensive flooding prompted the passage of many flood control measures. The Flood Control Act of 1944, (the Pick-Sloan Plan) created the Fort Randall and Gavins Point dams, causing major changes to the river's hydrology and habitats. Flora and fauna Along the river there are two major plant communities. The floodplain forest includes willow and cottonwood. The bluffs are covered by elm and oak. The annual floods