The Missouri River is the longest river in the US and even North America. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2,341 miles (3,767 km) before entering the Mississippi River north of St. Louis, Missouri.
The river takes drainage from a sparsely populated, semi-arid watershed of more than half a million square miles (1,300,000 km2), which includes parts of ten U.S. states and two Canadian provinces.
For over 12,000 years, people have depended on the Missouri River and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, most leading a nomadic lifestyle and dependent on enormous bison herds that once roamed through the Great Plains.