The New Student's Reference Work/Missouri (river)
Missouri, a river of the United States, the longest tributary of the Mississippi. The name means the Big Muddy. It is so much larger and longer than the Upper Mississippi that it ought to be considered the main river, and with the Lower Mississippi form the longest river in the world. It rises among the Rocky Mountains, near the border of Montana and Idaho, its general direction being southeast to the Mississippi, which it reaches, after crossing the whole state of Missouri, near St. Louis. It is 2,980 miles long, and can be navigated for about 2,500 miles. A narrow gorge made by walls 1,200 feet high and only 450 feet apart, called the Gates of the Rocky Mountains, through which the river flows, is about 400 miles from its source, and 145 miles further down are the Great Falls, of four cataracts, 26, 47, 19 and 87 feet high, separated by rapids.