In 1803, President Thomas Jefferson made a deal with France that doubled the size of the United States. The Louisiana Purchase added 828,000 square miles of land west of the Mississippi River. But nobody in the American government knew what was out there. Jefferson asked Meriwether Lewis and William Clark to find out. On May 14, 1804, the expedition set off from Camp Dubois near St. Louis with about 45 men. They traveled up the Missouri River in a large keelboat and two smaller canoes. The journey was full of challenges. The river had dangerous currents and hidden obstacles like fallen trees. Mosquitoes swarmed in thick clouds. In present-day North Dakota, they met Sacagawea, a young Shoshone woman who became an essential member of the team. She translated languages, identified edible plants, and her presence with her infant son signaled to other nations that the group was not a war party. The expedition crossed the Rocky Mountains, nearly starving in the process, and finally reached the Pacific Ocean in November 1805. They returned in September 1806, having traveled roughly 8,000 miles. Lewis and Clark brought back detailed maps, descriptions of 178 plants and 122 animals previously unknown to American science, and peaceful contact with dozens of Native nations.