Under President Jefferson, the United States purchased the Louisiana Territory in 1803 for a price of 3 cents per acre for some 828,000 square miles of land. It is considered one of the best land deals ever. Jefferson commissioned the expedition of Lewis and Clarke to explore this territory  from the Mississippi River to the Pacific Ocean. On 14 May 1804 this “Corps of Discovery” as it was called, left St. Louis with 45 men (only 33 would make the full journey) for the newly purchased American interior.

Traveling up the Missouri River in six canoes and two longboats they would winter in Dakota before crossing into Montana where they saw the Rocky Mountains for the first time. They would meet the Shoshone Indians on the other side of the Continental Divide, who would sell them horses. The journeyed through the Bitterroot Mountains, down the rapids of the Clearwater and Snake rivers, until they reached the Columbia River and to the sea. They arrived at the Pacific Ocean on 8 November 1805 and were the first European explorers to do this overland from the east. The paused for the winter and then made their journey back to St. Louis in the spring.

The journals that were kept noted longitude and latitude with detailed notes on soil, climate, animals, plants, and native peoples. They identified new plants and animals (the grizzly bear for one). They also named geographic locations after themselves, loved ones, friends and even their dog. They experienced a variety of diseases and injuries during their journey but only one person perished. Their expedition is considered one of the most consequential and remarkable in U.S. history. Their travels in Oregon would lead the U.S. to able claim territorial rights later.

Sources:

• Lewis and Clark Expedition (Britannica.com)
• Lewis and Clark Return to St. Louis (History.com)
• Louisiana Purchase (Britannica.com)