In 1804, President Thomas Jefferson commissioned Meriwether Lewis to explore lands west of the Mississippi River that comprised the Louisiana Purchase. Lewis chose William Clark as his co-leader for the exploration. During the course of over two years they confronted harsh weather, unforgiving terrain, treacherous waters, injuries, starvation, disease and both friendly and hostile Native Americans. Nevertheless, the approximately 8,000-mile journey was a huge success and provided new geographic, ecological and social information about the unexplored areas of North America.
During their exploration Lewis and Clark identified 178 plants and 122 animals not previously known to science. This included discovering or carefully describing for the first time at least seven Great Plains mammals, including the pronghorn, grizzly bear, swift fox, black-tailed prairie dog, white-tailed jackrabbit, bushy-tailed woodrat, and mule deer.