On his return journey in July 1806, Capt. Meriwether Lewis crossed the continental divide at Lewis and Clark Pass about 2 miles west of here, entering land of the Louisiana Purchase and returning to United States territory. He followed the ancient Indian trail known as the Road-to-the-Buffalo, a route used for centuries by mountain dwelling tribes including the Salish, Nez Perce, and Shoshone for excursions into the northern plains to hunt buffalo. The Corps of Discovery had split at Travelers Rest near Missoula. Capt. Clark's group took a southern route to the Jefferson River and the Three Forks, where it divided again, with the larger party retrieving canoes and descending the Jefferson and Missouri rivers to rejoin Lewis later, while a smaller party with Clark explored the Yellowstone River area. The entire expedition regrouped near the mouth of the Yellowstone. Lewis and his group went north to the Great Falls following the Nez Perce route, then split again at the Missouri, with the larger party left to portage boats, papers, and maps around the falls while Lewis led a smaller group farther north to meet the Blackfeet and determine how far the drainage of the Marias River extended. This exploration was intended to support a legitimate United States argument in establishing the farthest possible northern boundary between the U.S. and British Canada.