Lewis and Clark reached the eastern edge of the Great Plains.
Step-by-step explanation:
Lewis and Clark together involved in crossing the western portion of United States of America and started their mission in the year May 1804 to September 1806. This mission is also known as the Corps of Discovery Expedition.
Lewis was appointed by President Thomas Jefferson to explore the west lands of the Mississippi River. He started his journey with Clark as his partner.
Lewis and Clark reached the eastern edge of the great plain in summer 1804, after meeting Native Americans for the first time.