The Indians of Rocky Mountains called the right-bank tributary of Missouri the River of Yellow Stones, as the surface of its cliffs featured yellowish tone. The colonists from the Old World borrowed this name – Yellowstone. In 1805, an expedition found geothermal sources on the banks of the river. For half a year, the scientific community was hesitating, but in 1869, the expedition of David Folsom traveled upstream and reached the Yellowstone Lake. This expedition and other ones found geysers, canyons, caves, and volcanic caldera (later nicknamed super-volcano) in the Rocky Mountains on the banks of Yellowstone, on the territory of Idaho, Wyoming and Montana. There were so many interesting things in this region that President Ulysses Grant signed on March 1, 1872 the bill prescribing to protect the environment in the region of Yellowstone (both river and lake) in a special manner. This territory received the name of Yellowstone National Park. Today, this UNESCO World Heritage Site is visited by three million tourists annually. The area of Yellowstone National Park is 898.3 thousand hectares.