THE WILD WEST HISTORY

The Yellowstone River is a tributary of the Missouri, approximately 671 mi (1,080 km long), in the western United States. Considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National Park across the mountains and high plains of southern Montana and northern Wyoming. It is the longest undammed river in the lower 48 states.
It rises in northwestern Wyoming near Younts Peak at the continental divide in southwestern Park County. It flows northward through Yellowstone National Park, feeding and draining Yellowstone Lake, then dropping through Yellowstone Falls and forming the Grand Canyon of the Yellowstone within the confines of the park. It flows northward into Montana through the Absaroka Range and emerges from the mountains near the town of Livingston, where it turns eastward and northeastward, flowing across the northern Great Plains past the city of Billings.

East of Billings, it is joined by the Bighorn River. Further downriver, it is joined by the Tongue near the town of Miles City, and then by the Powder in eastern Montana. It joins the Missouri in extreme western North Dakota, upriver from the town of Williston at the Lake Sakakawea reservoir, with the lower 20 mi (32 km) of the river forming a narrow arm of the reservoir. At the confluence with the Missouri, the Yellowstone is actually the larger river.

The river was explored in 1806 by William Clark during the return voyage of the Lewis and Clark Expedition, and the Clarks Fork of the river was named for him. The Clarks Fork collects drainage from the south side of the Beartooth Mountains, runs eastward through Wyoming, and then turns north to run through Clark, Wyoming, Belfry, Montana, Bridger, Montana, and several other towns before joining up with the main river near Billings, Montana.

The Yellowstone River was an important artery of transportation for Native Americans as well as for white settlers by riverboat in the 19th century. In Montana, it has been used extensively for irrigation since the 1860s. In its upper reaches, within Yellowstone Park and the mountains of Montana, it is a popular destination for fly fishing.