From this area, the Water Trail follows the Vermillion River to its confluence with the Missouri River and then continues downstream through an exceptionally natural, scenic, and relatively undeveloped stretch marked by wide channels, islands, sandbars, braided waterways, and backwaters. In 1804, the Missouri flowed in a great bend beneath the Vermillion Bluffs near this site, where it met the Vermillion River, then known to Lewis & Clark as White Stone Creek, and that bend remained through the early settlement period as young Vermillion, built mostly below the bluff, served as a riverboat town. Spirit Mound, one of the few confirmed documented sites visited by the Lewis & Clark Expedition, was reached overland from the confluence on August 25, 1804, when Lewis and Clark, with 11 men and their dog, went to visit the "Mountain of little people or Spirits"; Clark recorded a tribal tradition that it was believed to be the residence of beings in human form with large heads, about 18 inches high, watchful and armed with sharp arrows. Geologically, Spirit Mound is a knob of resistant bedrock shaped by a Pleistocene glacier during the last ice age about 13,000 years ago, and today its 320-acre site has been restored to prairie and remains a sacred place for many Native Americans. The Great Flood of 1881 transformed both the town of Vermillion and the rivers, washing the town away, shifting the Missouri south several miles into a new channel, and leaving the Vermillion River to occupy the pre-1881 Missouri channel. Since 1957, both channels have deepened as dams have held back sediment and the river has scoured its bed, reducing natural meandering and channel migration. This section of the Missouri is among the last relatively natural stretches of America’s longest river, part of a National Recreational River designated under the Wild and Scenic Rivers Act and also part of the Lewis and Clark National Historic Trail.