Design of this stamp commemorated the U.S. Army Corps of Engineers' completion of America's most extensive canal system. The Ohio River's 46 locks and dams provided a dependable nine-foot channel between Pittsburgh, PA, and Cairo, IL, a distance of 981 miles. The lock shown on this stamp is not on the Ohio River, but Lock No. 5 on the Monongahela River. The Monongahela is one of the two rivers that meet at Pittsburgh to form the Ohio.