Upon leaving the Great Falls of the Missouri on July 15, 1805, the Lewis and Clark expedition began to search in earnest for the Shoshone from whom they hoped to purchase horses for their journey over the Rockies. The next day, Lewis identified an abandoned but recent Shoshone camp with a wickiup and signs of numerous horses, but the Indians remained elusive. The captains decided to split up and have Clark take a detachment ahead while Lewis brought up the boats and the rest of the Corps.

As Lewis and Clark continued their journey up the Missouri River in 1805, the Corps was moving further and further from civilization with every stroke of their paddles. Although the Corps had been made aware of the countless wonders to the west through conversations with the Mandans and Hidatsas, it was quite another thing to observe the wonders for themselves, and at seemingly every bend in the river there were new discoveries.

On August 31, 1803, Captain Meriwether Lewis departed from Fort Fayette, today’s Pittsburgh, in the keelboat the Corps of Discovery would take up the Missouri River and, six weeks later, arrived at the Falls of the Ohio and Clarksville, Indiana Territory. It was here, at the town founded by General George Rogers Clark, that Meriwether Lewis and William Clark, the General’s youngest brother, met again for the first time in seven years and commenced the most famous partnership in American history, two men so joined in American lore as to almost be inseparable. 

In 1801, Meriwether Lewis was a Captain serving as the paymaster for the First Infantry Regiment of the United States Army. In March, he received a letter from Thomas Jefferson, the newly inaugurated President, asking Lewis to become his private secretary. Lewis, whose family was friends with the Jefferson clan, accepted at once, and thus began a close working relationship, one in which Jefferson became a father figure to Lewis and mentored his young subordinate on policy matters, including his dreams of western exploration and expansion.

By the time they began to assemble the Corps of Discovery in the summer of 1803, Thomas Jefferson and Meriwether Lewis knew more than anyone else about the Louisiana Territory, that immense wilderness the country had recently purchased from France. Although Jefferson had never ventured more than fifty miles west from Monticello, he had dreamed of the trans-Mississippi and studied the region extensively over the previous two decades, even trying unsuccessfully to send exploratory expeditions on several occasions.