The Lewis and Clark Trail is a highway that approximates the path taken by Lewis and Clark in 1804-1806, between the St. Louis area and the Pacific Ocean. Like the Great River Road, it is marked along existing roadways, in this case mostly paralleling the Missouri and Columbia Rivers.
Roads followed include Interstate 29 in Iowa, the appropriately-numbered SD 1804, ND 1804, SD 1806, and ND 1806, and Washington State Route 14. Two separate routes of the trail are signed between St. Louis and East Fairview, North Dakota, one on each side of the Missouri.
The trail was conceived in the 1960s by the Lewis and Clark Trail Commission.
References
Lewis and Clark Trail Wikipedia(Text) CC BY-SA