Book excerpt: Few events in American history have shaped the nation like the Lewis and Clark Expedition. It opened the American West for settlement. It redrew the map of the United States. It identified an array of native peoples, spectacular places, fascinating creatures, and extraordinary flora unknown in "civilized" America. It defined the American nation as a land stretching from coast to coast-and it launched the spread of population in a mighty frontier migration unlike anything ever witnessed in America before or since. Lewis and Clark on the Trail of Discovery contains 19 chapters, detailing the expedition chronologically. A "museum in a book," this fascinating volume contains re-creations of original documents such as diary entries, letters, maps, and sketches-all meticulously reproduced so that the reader can actually handle and examine them. Among the documents included in the book are: The actual letter of credit Jefferson wrote to Lewis committing the U.S. government to pay for the expedition. The code Thomas Jefferson provided to Lewis for sending secret messages. Clark's sketch of the technique some Indians used to flatten their heads, a sign of prestige. Clark's letter of gratitude to Sacagawea, a Shoshone teenager who helped the expedition. A newspaper account of the expedition's return to St. Louis.