The united states has several immensely long rivers. There are a large number of rivers in the eastern part of the nation, the longest of which is the Missouri (3,942 km) , a tributary of the mississippi(3,760 km); the mississippi - the ohio and tennessee - are more than 1,250 km long . In the west the rio grande, which forms part of the united states mexico border, flows for 3,016 km and only the colorado (2320)