Harper's Encyclopedia of United States History
Benson Lossing, Ed.

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Missouri River, the

Recent investigations seem to make it certain that the Mississippi River, from its confluence with the Missouri, should be called the Missouri; and that the Mississippi proper, above that confluence, is a branch of the Missouri. Above their confluence the Mississippi drains 169,000 square miles, and the Missouri drains 518,000 square miles. From that point to Lake Itasca the length of the Mississippi is 1,330 miles; while that of the Missouri, from its sources in Madison, Red Rock, and Gallatin lakes, is about 3,047 miles. At the confluence of the rivers the Mississippi has a mean discharge of 105,000 cubic feet of water a second, and the Missouri 120,000 cubic feet a second. Above that confluence the Missouri is navigable to Fort Benton, Mont., by good-sized steamboats, a distance of 2,682 miles, or more than twice the length of the Mississippi from Lake Itasca to its confluence with the Missouri. Reckoning the Mississippi below the confluence as the Missouri makes the latter, to the Gulf—4,347 miles —the longest river in the world.