One year after the United States doubled its territory with the Louisiana
Purchase, the Lewis and Clark expedition left St. Louis, Missouri, on a 
mission to explore the Northwest from the Mississippi River to the
Pacific Ocean.

Even before the U.S. government concluded purchase negotiations with
France, President Thomas Jefferson commissioned his private secretary Meriwether Lewis and William Clark, an army captain, to lead an expedition
into what is now the U.S. Northwest. On May 14, the “Corps of Discovery”
–featuring approximately 45 men (although only an approximate 33 men
would make the full journey)–left St. Louis for the American interior.

                       Meriwether Lewis and William Clark.