In November 1805, the Corps of Discovery, led by Meriwether Lewis and William Clark, reached the Pacific Ocean, fulfilling the primary geographical objective of their journey. Reaching the coast, however, marked only the halfway point, initiating a new phase of planning before their return east. Their subsequent activities focused on survival, maximizing scientific and geographical knowledge, and navigating a path back to St. Louis.
Wintering at Fort Clatsop
Upon reaching the mouth of the Columbia River, the leaders determined the expedition required a permanent structure to endure the rainy winter months. They established Fort Clatsop, named after the local indigenous tribe, on the south bank of the Netul River (now the Lewis and Clark River). This encampment provided necessary shelter from the relentless, damp weather that characterized the coastal winter.
Securing provisions became an immediate priority, with men dispatched daily to hunt for elk and deer. The high moisture content and constant rainfall made meat preservation difficult. Much of the elk meat spoiled quickly, challenging the expedition’s food security throughout the winter.
To cure and preserve the limited meat supplies, the party needed salt, a scarce resource in the interior. A small detachment was sent several miles south to the coast to construct a salt cairn. Over several weeks, they boiled hundreds of gallons of seawater to yield approximately 28 gallons of crystallized salt necessary for the return journey.
The Corps maintained frequent interactions with the local Chinook and Clatsop tribes. These groups were sophisticated traders who controlled access to resources and markets along the coast. The expedition relied on them to trade for furs and, occasionally, fresh foods like fish and berries.
The nine-week period at Fort Clatsop was marked by physical discomfort due to pervasive dampness, which ruined clothing and leather goods. Despite the hardship, the officers used the time to meticulously organize the scientific data, journals, and maps accumulated over the preceding two years. This effort prepared them for the final phase of their mission.
The Decision to Divide the Corps
As the expedition prepared to depart Fort Clatsop in March 1806, Lewis and Clark implemented a strategic change for the return journey. The goal shifted from simple survival to maximizing geographical and scientific data collected for President Jefferson. They recognized the need to explore areas previously bypassed on the westbound route.
The leaders concluded that splitting the Corps would allow them to simultaneously explore different major tributaries of the Missouri River system. This division was intended to cover a broader swath of territory in a shorter amount of time. A primary objective was to determine the northern and southern boundaries of the Louisiana Purchase lands.
A secondary reason for the split was the search for a more direct water passage back to the settlements. By sending separate parties to navigate previously unmapped rivers, they hoped to identify potential shortcuts for future American traders and explorers. This planning was concluded before leaving the Pacific watershed.
Mapping Separate Return Routes
The Corps traveled together until they reached the Bitterroot Mountains and the Great Falls of the Missouri River. There, the pre-planned division was executed, with Captain Lewis leading the northern party and Captain Clark taking the southern contingent. This separation allowed for the collection of two distinct sets of geographic and natural history data.
Lewis’s party proceeded north from the Great Falls to explore the Marias River, a major tributary they had not fully investigated. The instruction was to follow the river to its northernmost navigable point, confirming the territorial limits of the Louisiana Purchase. While exploring the upper Marias, Lewis’s small group encountered Blackfeet warriors. The interaction quickly turned hostile when the Blackfeet attempted to steal the expedition’s rifles and horses, resulting in the deaths of two Blackfeet men.
Following the incident, Lewis and his men rode over 100 miles in a single day to distance themselves and avoid further conflict. They then navigated the Missouri River rapidly downstream, collecting samples and mapping the terrain as they proceeded toward the rendezvous point.
Meanwhile, Clark’s party traveled south to the headwaters of the Yellowstone River, another major unmapped waterway feeding the Missouri. The objective was to trace the river from its source to its confluence, establishing a detailed geographic record. Clark’s group included Sacagawea, who served as a guide through her knowledge of the area.
Clark utilized the river for travel, constructing canoes and navigating the rugged, fast-moving Yellowstone. His party systematically mapped the river’s course, noting its tributaries, geological features, and potential for navigation. This documentation provided the first extensive geographical survey of the entire Yellowstone drainage basin.
The combined effort of the two routes yielded comprehensive data that fulfilled the expedition’s mandate better than a single-path return. Lewis’s route provided clarity on the northern reach of the territory, while Clark’s exploration of the Yellowstone provided detailed knowledge of the southern area.
The Expedition’s Final Leg
The two separate parties reunited near the confluence of the Yellowstone and Missouri Rivers in August 1806, having completed their exploration assignments. The delay allowed both groups to complete their comprehensive mapping. With the Corps reassembled, they began the swift descent of the Missouri River.
Traveling eastward, the current of the Missouri River greatly accelerated their speed compared to the laborious outbound travel. The Corps covered the distance from the upper Missouri to St. Louis in a fraction of the time, often covering 70 to 80 miles per day. They paused only briefly to resupply.
The expedition arrived back in St. Louis in September 1806, nearly two and a half years after their departure. Their return was unexpected, as many in the East had presumed the party lost in the western wilderness. Their arrival provided President Jefferson with definitive geographic and scientific proof that the journey had achieved its objectives.