The Arkansas Basin is the watershed of the Arkansas River, a tributary of the Mississippi River. Its headwaters are in central Colorado above Salida, Colorado. It exits the Rocky Mountains at Canon City, Colorado and flows through Pueblo, Colorado and other Arkansas Valley towns in southeastern Colorado before flowing into Kansas, then Arkansas, where it enters the Mississippi. It is dammed above Pueblo at Pueblo Reservoir and further east at John Martin Reservoir near Lamar, Colorado.