The Yellowstone River rises on the continental divide near Younts Peak in Wyoming's Teton Wilderness. It flows north through Yellowstone National Park, enters Montana near Gardiner, and passes through the Paradise Valley to Livingston. It then flows northeasterly across the state through Billings, Miles City, Glendive, and Sidney. The Yellowstone joins the Missouri in North Dakota just east of Fort Union. It is the longest undammed, free-flowing river in the contiguous United States, and drains about a quarter of Montana (36,000 square miles (93,000 km2)).

Which direction does the Yellowstone River flow through the national park?