The design of this stamp paid tribute to the important waterway and the economic potential of the $1.2 billion Arkansas River Navigation project. The Arkansas River is a major western tributary of the Mississippi River system. Rising in the Rocky Mountains of central Colorado, it flows east into Kansas, turns southeast through Oklahoma, and crosses Arkansas to enter the Mississippi. Dams on the Arkansas have created reservoirs, including the John Martin in Colorado, the Keystone in Oklahoma, and the Dardanelle in Arkansas. Widening the river has made it navigable for 750 miles (1,210 km) from its mouth.