Yellowstone Park, carved out of territorial Wyoming, Montana, and Idaho, is a rough-edged rectangle of 3,500 square miles that straddles the twisting course of the Continental Divide. It is a geological circus, a unique creation of ancient volcanoes and glaciers, flanked on the southeast and east by the Absaroka Range, on the north by the Snowy Range, on the northwest by the Gallatin and Madison ranges, on the west by the Centennial Range, and on the south by the Teton Mountains. From the Park flow the headwaters of two continental rivers and their major tributaries. From here the Snake River arcs southward toward Jackson’s Hole and the cathedral-like Tetons, destined to join the Columbia River and the Pacific Ocean. Here the Firehole and Gibbon rivers, draining the principal geyser basins, unite to become the Madison River, and here also arises the Gallatin, these being two of the Three Forks of the Missouri. Here arises a branch of the North Fork of the Shoshone River, a tributary of the Bighorn. And here, after its birth near Two Ocean Pass, begins the mighty Yellowstone River which, after passing through its vast mirror-like lake and its prismatic canyon, flows out onto the plains to receive the Bighorn and join the Missouri on its marathon journey to the Mississippi River and the Gulf of Mexico. [Illustration: Indians at Jackson Lake.] This region held a fortune in coveted beaver skins, but it was remote, snowbound, haunted by the vindictive Blackfeet, and plagued by weird visions, sulphurous fumes, and uncanny noises. Here indeed was fertile soil for a legend. On a clear day Yellowstone Park visitors can see to the south the mountain spires which identify Grand Teton National Park of Wyoming, an indefinable shape of 500 square miles. (The actual boundaries of these neighboring parks are separated by a scant five miles.) The Tetons are perhaps the most distinctive of the granite giants which comprise the Rocky Mountains. A series of sharp pyramids of naked rock, the peaks stand like sharks’ teeth against the sky. The most precipitous sides and the most needle-like summit belong to the highest of these, the Grand Teton, which rises over 7,000 feet from its immediate base, nearly 14,000 feet above the level of the distant sea. The Teton Mountains are the most conspicuous landmarks of a region which contains the scrambled sources of the three greatest river systems of continental United States. As we have seen, Yellowstone Park to the north gives birth to the eastward-flowing Missouri and the westward flowing Columbia waters. East of the Tetons, in the Wind River Mountains, is the head of Green River which rolls southward to merge into the mighty Colorado River, tumbling through the arid lands to the Gulf of California.