On August 25, 1804, the Lewis and Clark expedition walked to the mounds from their camp.

Spirit Mound

Spirit Mound Historic Prairie is a state park of South Dakota, USA, featuring a prominent hill on the Great Plains. The Plains Indians of the region considered Spirit Mound the home of dangerous spirits or little people; members of the Lewis and Clark Expedition climbed it on August 25, 1804. The park was established in 2002.

• http://en.wikipedia.org/wiki/Spirit Mound Historic Prairie