On June 20, 1803, President Thomas Jefferson instructed Meriwether Lewis to explore the Missouri River and its principal streams to find the most direct and practicable water communication across the continent for commerce, by way of connections with the waters of the Pacific Ocean. He directed that, beginning at the mouth of the Missouri, the expedition take observations of latitude and longitude at all remarkable points on the river, especially at the mouths of rivers, at rapids, at islands, and at other places and objects marked by durable natural characteristics so they could be recognized later, while the course between those points could be supplied by compass, log-line, and time. William Clark, the expedition's mapmaker, and the crew departed from Wood River on May 14, 1804, and Clark was joined by Meriwether Lewis on May 20 in St. Charles. The expedition explored the river with a 55-foot keelboat as its largest vessel.
