Missouri River

Largest branch of the Mi i ippi. It heads in the mountains of s.w. Montana, in three forks, the Jefferson, Madison, and Gall at in, flows at first n., then e., and finally s.e. to its mouth just above St. Louis. Its principal branches are the Yellow stone, Cheyenne, Platte, and Kansas on the right, and the James and Big Sioux on the left. Its heads are in high mountains, its middle course is through arid plains, and its lower course in a fertile region. Its annual flood is in June. Length 2,908 m., drainage area 527,672 sq. m. It is navigable to Great Falls, Mon., at high stage of water. Average flow 121,900 cu. ft. per second.