Since the time of Columbus, explorers dreamed of a water passage across the North American continent. President Thomas Jefferson shared this dream. He conceived the Corps of Discovery to travel up the Missouri River to the Rocky Mountains and westward along possible river routes to the Pacific Ocean. Meriwether Lewis and William Clark led this expedition of 1804–6. Along the way they filled hundreds of notebook pages with observations of the geography, Indian tribes, and natural history of the trans-Mississippi West. The late-summer and fall months of 1805 were the most difficult period of Lewis and Clark's journey. This volume documents their travels from the Three Forks of the Missouri River in present-day Montana to the Cascades of the Columbia River on today's Washington-Oregon border, including the expedition's progress over the rugged Bitterroot Mountains, along the nearly impenetrable Lolo Trail. Along the way, the explorers encounter Shoshones, Flatheads, Nez Perces, and other Indian tribes, some of whom had never before met white people.