In 1803, during the presidency of Thomas Jefferson, France sold a vast portion of central North America to the United States of America. This "Louisiana Purchase" was largely unexplored. Jefferson sent out the Corps of Discovery, under Lewis and Clark, to scientifically document the territory. In 1804 the Lewis and Clark expedition traveled up the Missouri and set-up camp near what would become Sioux City, Iowa. On August 20, a member of the expedition, Sgt. Charles Floyd died of "bilous colic" and was buried on a bluff overlooking the river. At the time of Lewis and Clark, the Omaha tribe of Native Americans were present just downstream from this region, and the Yankton Sioux were upstream. William Thompson established a trading post near Floyd's Bluff in 1848, and had early ambitions for founding a city. However, Thompson's hopes were never realized; settlers further upriver, between the Floyd and Big Sioux rivers, met with more success.