M ARCH io, i805, found the Corps of Northwestern Discovery, the official name for the Lewis and Clark expedition, huddled behind the log walls of Fort Mandan. The palisade sheltered the exploring party from sharp winds howling down the Dakota plains. On that bitter cold day Capt. William Clark took time to perform one of the many duties assigned by President Thomas Jefferson. Clark listened patiently while Black Cat, headman of the Nuptadi Mandan village, related manly] Strang accounts of his nation.' A year later and half a continent away, Meriwether Lewis employed all his naturalist's skill to complete another expedition task. He carefully described the appearance and behavior of the western coot, taking note of the ways Pacific coast ducks differed from those seen along the Ohio and Mississippi rivers.2 What Lewis and Clark were doing on either side of the trans-Mississippi West represents something fundamental about exploration in the time between I 7 6o and i 8 I 5. That half century witnessed a dramatic expansion of scientific and geographic knowledge about the West beyond the Great Lakes. Explorers were the vanguard for an expanding intellectual frontier. But the period saw more than a growing empire of the mind. North of Lake Superior and south and west of St. Louis, the continent became the arena for a clash of national empires. Spaniards, English, Canadians, Russians, and native Americans all vied for western dominion. The international and multicultural conflicts that had shaped tidewater and woodland destinies now moved west to a final battleground. On that often bloody field, explorers became the advance forces probing for passes and rivers to satisfy the sovereign logic of Washington, D.C., London, Montreal, Madrid, and St. Petersburg. The exploration of the West after I76o was far more than the colorful exploits of such as Alexander Mackenzie, Simon Fraser, Lewis and Clark, and Zebulon Montgomery