The U.S. Army Corps of Engineers welcomes you to Clarence Cannon Dam and Mark Twain Lake. Many recreational opportunities await you on this 55,000-acre land and water project spanning the Salt River Valley in Northeast Missouri. Rich in history and home to Samuel Clemens (Mark Twain) there are many local attractions to choose from. The lake is located in Ralls and Monroe Counties, 28 miles southwest of Hannibal, MO and 120 miles northwest of St. Louis.