Lewis was appointed by President Jefferson to lead an expedition through the recently purchased Louisiana Territory. He asked Clark to join him. They camped in Illinois near St. Louis while they organized.

On May 14, 1804, the expedition set out in several boats up the Missouri River. They wintered in North Dakota with the Mandan Indians. They enlisted Sacajawea as a guide. She helped them obtain horses for their passage across the great divide. They built canoes and descended the Columbia River to its mouth.

Fort Clatsop was built, near Astoria, to provide shelter for the winter. There were no ships available to return by sea. They determined to return overland. They returned to St. Louis September 23, 1806. The country had given them up for lost. Now they were heros and the names of Lewis and Clark would be forever linked.

The two men have been jointly honored with many medals. They appear on the Lewis and Clark Exposition Gold Dollars. Lewis appears on the date side. Clark appears on the denomination side. Dies were by Charles E. Barber from Charles Wilson Peale's portraits. Authorized mintage was 250,000 pieces. In 1904 25,000 were struck, 9997 issued and the remaining 15003 melted. In 1905 35,000 were minted, 10,000 issued and 15,000 melted.

The Lewis and Clark Centennial Exposition was held in Portland, Oregon, June 1 to October 14, 1905. Farran Zerbe supervised creation of a numismatic exhibit and supervised sales of coins and medals. An official medal was struck at the mint exhibit. The 35 mm medal was available in bronze, silver and gold plated bronze. Several unofficial medals were also issued.

Lewis and Clark appear on paper money:

$10 Legal Tender Notes, series of 1901