Although Lewis and Clark were not the first whites to cross the North American continent — Scottish fur trader Alexander Mackenzie traversed Canada a decade earlier — their epic journey ranks high in the annals of exploration. Even before the Louisiana Purchase, President Thomas Jefferson was planning a transcontinental expedition and in 1804, he commissioned his private secretary, Captain Meriwether Lewis, and another young army officer, William Clark, to explore the vast domain. The Lewis and Clark party included Clark’s slave York and later on, Sacagawea, the Shoshone Indian wife of the group’s interpreter. Setting out from St. Louis in May, 1804, they followed the Missouri to its headwaters, crossed the Continental Divide with Shoshone help secured by Sacagawea, and descended the Snake and Columbia rivers to reach the Pacific in November, 1805. Heading east soon afterward, the explorers were back in St. Louis in September, 1806, having traveled more than 8,000 miles. They brought back maps, drawings, botanical and geological specimens and data on the Indians. Though unsuccessful in its search for a water route to the Pacific, the expedition strengthened American claims to the Oregon Territory and stimulated the fur trade and Western Settlement.

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