Yellowstone River: Source to Mouth

The Yellowstone River is the longest undammed river in the contiguous U.S.

Source

It begins in the Absaroka Range of northwestern Wyoming, at the confluence of the North, Middle, and South Forks. The North Fork, originating near Yellowstone National Park, is the longest.

Course

The river flows north through Wyoming, into Montana, then northeast across eastern Montana and a corner of North Dakota.

Mouth

It ends at the confluence with the Missouri River in northeastern Montana, near Fort Union. The Missouri continues to the Mississippi and finally the Gulf of Mexico.

The Yellowstone is prized for its scenery, wildlife, fishing, and historical significance.