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. This volume covers the last leg of the party’s route from the Cascades of the Columbia River to the Pacific Coast and their stay at Fort Clatsop, near the river’s mouth, until the spring of 1806. Travel and exploration were hampered by miserable weather. While in winter quarters, Lewis wrote detailed reports on natural phenomena and Indian life. These descriptions were accompanied by sketches of plants and animals as well as of Indians and their canoes, tools, and clothing. Gary E. Moulton is Thomas C. Sorensen Professor of American History at the University of Nebraska and the recipient of the J. Franklin Jameson Award of the American Historical Association for the editing of these journals.