The Lewis and Clark expedition began on May 14, 1804 when the Corps of Discovery left Camp Wood River in Illinois. In February 1803, Congress had approved its funding after President Thomas Jefferson urged them to do so. The expedition was to follow the Missouri River to its source, cross the continental divide and then follow the Columbia River to its mouth at the Pacific Ocean. Clark often remained on the 55 foot keelboat or the two pirogues making charts of the course and maps while Lewis was on land studying the rocks, animals, soils and plants. They returned to St Louis on September 23, 1806.