On October 20, 1804, Clark wrote, “I saw an old remains of a villige on the Side of a hill which the Chief with us Too né tels me that nation lived in a number villages on each Side of the river and the Troubleson Seauex caused them to move about 40 miles higher up where they remained a fiew years & moved to the place they now live”. The site, located near the confluence of the Heart River with the Missouri River, was a former Mandan settlement that has come to be known as On-A-Slant Village. Estimated to have included about 75 earthlodges and perhaps 1,000 residents, the village had likely existed for over 200 years before a 1781 smallpox epidemic decimated the population.
A military post named Fort Abraham Lincoln was established at the site in 1872. It became a base of operations in the U.S. Army’s campaign against the Lakota Sioux and Northern Cheyenne nations during 1876 and 1877. The fort was abandoned in 1891, after the completion of the railroad into Montana reduced its strategic importance. The site was designated Fort Abraham Lincoln State Park in 1907. Five earthlodges have since been reconstructed on the site of On-A-Slant Village, and interpretive tours offer an introduction to historic Mandan culture. The site retains archeological evidence of the original village.