Lewis and Clark became the first scientists to document the natural history of the American West. They were careful and accurate observers, and the experts of the time had trained Lewis in natural history and the methods of collecting samples of plants and animals. From St. Louis up the Missouri River, over the Continental Divide, down the Columbia River to the Pacific Ocean and back again, they recorded 178 plants and 122 animals previously unknown to science. Many of their other observations contributed additional information to scientific knowledge.

    Today, the U.S. Fish and Wildlife Service manages many of the species documented by Lewis and Clark. Modern wildlife biologists still consult Lewis and Clark's journals for information on the status of wildlife species 200 years ago.