Missouri River

The Lewis and Clark Expedition explored the Missouri river to its source, onward to the Oregon Territory, then to the Columbia River into the Pacific ocean, the first ocean-to-ocean and back trip across the United States.
 Meriwether Lewis and William Clark United States 1804 Missouri River

The Lewis and Clark Expedition explored the Missouri river to its source, onward to the Oregon Territory, then to the Columbia River into the Pacific ocean, the first ocean-to-ocean and back trip across the United States.