Natives living east of the Mississippi for their lands, as well as payments to Natives living in parts of the west outside the Louisiana Purchase. Even before the purchase, Jefferson was planning expeditions to explore and map the lands. He charged Lewis and Clark to "explore the Missouri River, and such principal stream of it, as, by its course and communication with the waters of the Pacific Ocean; whether the Columbia, Oregon, Colorado, or any other river may offer the most direct and practicable communication across the continent for commerce". Jefferson also instructed the expedition to study the region's native tribes (including their morals, language, and culture), weather, soil, rivers, commercial trading, and animal and plant life. Entrepreneurs, most notably John Jacob Astor quickly seized the opportunity and expanded fur trading operations into the Pacific Northwest. Astor's "Fort Astoria" (later Fort George), at the mouth of the Columbia River, became the first permanent white settlement in that area, although it was not profitable for Astor. He set up the American Fur Company in an attempt to break the hold that the Hudson's Bay Company monopoly had over the region. By 1820, Astor had taken over independent traders to create a profitable monopoly; he left the business as a multi-millionaire in 1834. The fur trade As the frontier moved west, trappers and hunters moved ahead of settlers, searching out new supplies of beaver and other skins for shipment to Europe. The hunters were the first Europeans in much of the Old West and they formed the first working relationships with the Native Americans in the West. They added extensive knowledge of the Northwest terrain, including the important South Pass through the central Rocky Mountains. Discovered about 1812, it later became a major route for settlers to Oregon and Washington. By 1820, however, a new "brigade-rendezvous" system sent company men in "brigades" cross-country on long expeditions, bypassing many tribes. It also encouraged "free trappers" to explore new regions on their own. At the end of the gathering season, the trappers would "rendezvous" and turn in their goods for pay at river ports along the Green River, Upper Missouri, and the Upper Mississippi. St. Louis was the largest of the rendezvous towns. By 1830, however, fashions changed and beaver hats were replaced by silk hats, ending the demand for expensive American furs. Thus ended the era of the mountain men, trappers, and scouts