Early French fur traders gave the Yellowstone River its name, La Roche Jaune, or the River of the Yellow Rock, for the orange and yellow rimrocks along its valley. Fed by snowfall in the mountains around Yellowstone Lake in Yellowstone National Park, the river runs through eastern Montana and joins the Missouri River in North Dakota. At 678 miles long, it is the largest undammed river in the lower 48 of the United States. The Crow and Northern Cheyenne called it Elk River. Flowing from west to east, it changes in water temperature, sediment, and fish species; near Billings it begins shifting from cold, swift water to warmer, wider channels where trout and walleye can both be found. At Billings, its flow ranges from 2,500 cubic feet per second in winter to more than 25,000 cubic feet per second during late spring flooding.