The United States in the late 1700s was different than the country today. It was only made up of the eastern part of the country it is today. By 1804, the United States got more land to the west. But the people in the United States knew very little about this land.

President Thomas Jefferson sent a group of men to explore the western land. The group was called the Corps of Discovery. The leaders were Meriwether Lewis and William Clark.

The Corps of Discovery started exploring in May 1804. They went from the Missouri River and traveled across the Rocky Mountains. After that, they went from the Columbia River to the Pacific Ocean.

Along the way, Lewis and Clark made maps. They also took notes about the animals and plants. The maps and notes had a lot of information.

President Jefferson also wanted them to trade goods with the Native Americans in the western land. But first, the Corps needed to get to know these Native Americans. Along the way, a Native American woman named Sacagawea joined the Corps of Discovery. She was a big help to the Corps of Discovery because she was able to communicate with the Native Americans. The Corps was able to meet different Native American tribes with her help.

The Corps of Discovery returned back east in September 1806. After they came back, they shared information with the American people in the east about the land and the Native American people they discovered out west.