We cannot see the American West exactly as Lewis and Clark saw it. The land and the rivers have been altered forever both by natural changes and by the people who came after Lewis and Clark. But we do have a window back in time through the journals of Lewis and Clark B to glimpse through their eyes the ever-changing Missouri River, dangerous and frightening encounters with grizzly bears that give us a sense of their abundance and distribution, or elk as a dietary staple.
Human settlement and development have altered large segments of Lewis and Clark's trail. Dams block rivers; reservoirs flood shorelines; dikes channelize rivers; farms have replaced prairie; cities and highways line the route. Wildlife species abundance and distribution has changed. For example, when Lewis and Clark crossed the continent they found elk abundant on the plains and scarce in the mountains – exactly the opposite distribution from today. Some of the species they saw regularly are now scarce.