The tale of an expedition into territory ""mysterious as Mars,"" told with the Newbery Honor author's characteristic clarity and enthusiasm. In the early 19th century, the interior of this country was thought to hide any number of oddities: strange monsters, mountains of salt, a lost Welsh tribe. In an effort to discover the facts, as well as to map out trade routes, President Jefferson dispatched a small party of soldiers westward on the Missouri River. Along with guides and interpreters (notably the young Shoshoni, Sacagawea) and Clark's black slave, York, this group collected samples of previously unknown wildlife, produced excellent maps and, most importantly, witnessed a panorama of Native American life and customs. The author makes this all sound like the grand adventure it was, though she also carefully notes the drastic effects of trade, whiskey, and smallpox on native cultures. A large selection of 19th-century illustrations complements and extends the text; disappointingly, all are reproduced in black-and-white, and many are murky. Andrist's To the Pacific with Lewis and Clark (American Heritage) may be more appealing visually, but this makes more engrossing reading. Index, bibliography, and excellent notes are appended.