The vast Yellowstone National Park, stretching over regions of Wyoming, Montana, and Idaho, was the first US National Park when it was established in 1872. Famous for its scenery, wildlife, and geothermal activity—most notably, the geyser known as Old Faithful—Yellowstone covers almost 3,500 square miles (9,000 square kilometers) of mountainous countryside. The park boasts one of the largest high-altitude lakes in North America (Yellowstone Lake), the longest undammed river in the contiguous United States (Yellowstone River), and even its own Grand Canyon.