Writing in informal language with a bit of wry humor, Dalton invites readers to imagine the West that Lewis and Clark found, revealing the dynamic features of nature and the dramatic changes that earlier peoples brought about. He explains surprising facts, ranging from why Indians used cottonwood bark as winter feed for horses to why the explorers experienced gastric distress with some foods, and even why the Expedition's dog would have been well-advised to avoid a diet of salmon.  (PNW254, $39.95)