President Jefferson was determined to have the United States explore the west. He had been working towards exploring the area since the time he served in the Washington cabinet. By the time he became President, the US knew a great deal about the west coast. Jefferson was further spurred by exploration that had taken place of Western Canada.
Jefferson decided to appoint his personal secretary Meriwether Lewis to lead the expedition. Lewis appointed his old friend William Clark as his second in command.
On May 14, 1804, the Lewis and Clark expedition set off from St Louis. The crew consisted of 32 soldiers and 10 civilians. They headed up the Missouri River; as far as South Fork, Montana. They spent the first winter among the Mandan Indians in South Dakota. In the spring, they made contact with the Shoshone Indians, who provided them with horses and squaws to carry baggage.
They crossed the Rocky Mountains, and were able to float down the Clearwater River, onto the Snake River, and then onto the Columbia River. Then, on November 5, 1805, they reached the Pacific Ocean.
The expedition returned to St. Louis, Missouri, on September 23, 1806.