On October 24, 1804, the Corps reached a great trade center and the last mapped landmark for nearly 1,000 miles (1,609 kilometers): the earth-lodge villages of the Mandan and Hidatsa tribes. Here they built their winter quarters, Fort Mandan, and fairly dove into tribal life. The Mandan sought them out for celebrations and bison hunts.

On April 7, 1805, as the Corps prepared to leave after a brutal but happy winter, Lewis wrote, “we were now about to penetrate a country...on which the foot of civilized man had never trodden....I could but esteem this moment...as among the most happy of my life.”