Yellowstone
a river of the United States, which rises in the Rocky Ly Mountains, about lat. 44° N. and lon. 110° W. After a course of about 25 miles it passes through the lake of the same name, and runs N. through the Yellowstone National Park. Soon after issuing from the lake the river makes at intervals a series of falls (the last being 300 feet high), and traverses cañons, one of which, the Great Cañon, is 30 miles in length, its steep sides being colored in bright hues and shaped in great variety of fantastic forms. Running in a N. E. direction the river ultimately joins the Missouri about lat. 48° YEMEN N., after a course of about 1,100 miles.
Steamers can ascend it for 300 miles to the mouth of the Big Horn, which is its largest affluent.