Final answer:
The Lewis and Clark Expedition, a historic American exploration, returned to St. Louis in 1806 after facing various challenges and spending a winter along the Pacific coast.
Step-by-step explanation:
The expedition that returned to St. Louis is most commonly known as the Lewis and Clark Expedition or the Corps of Discovery.
After navigating through numerous challenges, including the harsh conditions in the Bitterroot Mountains of Montana and spending a winter on the Pacific coast, the expedition returned to St. Louis in 1806. This journey was a significant event in American history, demonstrating the resilience and determination of the explorers and paving the way for western expansion.