Lewis and Clark Expedition journals. US explorers Meriwether Lewis (1774-1809) and William Clark (1770-1838) led an expedition to find a route leading to the Pacific coast of the USA. Starting from a camp near St Louis, the expedition travelled to the coast of what is now Oregon and returned along the same route. The journey lasted from May 1804 to September 1806, in which time they covered almost 13,000 kilometres. The expedition, commissioned by President Thomas Jefferson and sponsored by the American Philosophical Society, produced numerous new discoveries in sciences such as geography, meteorology, botany, zoology and ethnology.