An ambitious, historic attempt to explore and document an untamed American frontier unfolds in this rousing adventure drama. In 1803, Meriwether Lewis (Fred MacMurray) and William Clark (Charlton Heston), with President Thomas Jefferson's (Herbert Heyes)'s blessing, embarked on the government-sponsored Lewis and Clark Expedition - an attempt to discover a water route connecting St. Louis, Missouri, with the Pacific Ocean. Their trek takes them through the magnificent, danger-filled territory of the Pacific Northwest, with guidance from the Shoshone woman Sacagawea (Donna Reed).