Reaching Familiar Territory: Meriwether Lewis at Lewis and Clark Pass

By editor

Lincoln, Lewis and Clark County, Montana

On the morning of July 3, 1806, Captain Meriwether Lewis and nine men departed from Travelers' Rest, the encampment near present-day Lolo, Montana, where the Corps of Discovery had spent the winter of 1805-1806. This location lay nestled in a broad valley carved by the Bitterroot River, where the remnants of last winter’s camp still lingered amid the ponderosa pines (Pinus ponderosa) and Douglas firs (Pseudotsuga menziesii). The air was crisp, the smell of damp earth and pine needles mingling with the faintest trace of smoke from their fires. The expedition, having accomplished its westward journey to the Pacific, now faced a return to the Missouri River, but with a deliberate divergence. Lewis and Clark had agreed to split their command in an effort to explore a greater expanse of the northern continent before concluding their odyssey. Clark planned to follow the Yellowstone River southeast, while Lewis would strike more directly eastward, crossing the Continental Divide along a route known to the native peoples as the Road to the Buffalo.

This ancient trail, well-known among the Nez Perce and Salish, had been etched into the landscape over centuries by the steady tread of Indian hunters and their travois, deeply gouged into the soft earth by the passage of countless feet and dogs. Lewis, relying on the knowledge of his Nez Perce guides, set out to follow this path -- a route that promised a swift passage across the rugged divides of the Rocky Mountains to the bison-rich plains east of the mountains. The trail was no mere footpath but a corridor shaped by the seasonal movement of animals and humans alike, a conduit between ecosystems as distinct as the moist western forests and the expansive eastern grasslands.

By July 6, Lewis and his party had pressed eastward along the Blackfoot River, skirting the edges of what is now Lincoln, Montana. The topography here unfolds as a series of terraces descending from the mountains, with the river valley flanked by conifers and groves of quaking aspen (Populus tremuloides). The Blackfoot's waters, fed by snowmelt from the Cabinet Mountains to the northwest, carved a sinuous course through sedimentary layers of Cretaceous age -- sandstones and shales laid down some 70 million years ago during a time when shallow seas covered much of Montana. The trail was unmistakable, the deep ruts of the travois wheels and the impressions of moccasined feet guiding the men along a path worn deep into the earth.

Navigating this terrain, Lewis no doubt noted the rich biodiversity surrounding him. The song of the western tanager (Piranga ludoviciana) and the sharp call of the Clark’s nutcracker (Nucifraga columbiana) rose from the forest canopy, while mule deer (Odocoileus hemionus) grazed cautiously in the brush. The presence of these animals must have signaled to the party the vitality of the landscape and underscored the seasonal rhythms that shaped the lives of both wildlife and native peoples.

On July 7, the party reached the summit of what would come to be known as Lewis and Clark Pass, nestled at an elevation of approximately 6,424 feet along the Continental Divide. Here the granite and gneiss bedrock of the Rocky Mountains, formed over a billion years ago during Precambrian orogenies, thrust upward, bearing the weight of ancient geological forces. The pass itself offered a relatively gentle ascent on the western side, a low gap among towering peaks and ridges that had resisted erosion longer than the surrounding sedimentary formations. This divide separated two great watersheds: on one side, the Columbia River basin draining west to the Pacific; on the other, the Missouri River basin feeding the vast Mississippi watershed.

In his journal entry for that day, Lewis expressed a keen awareness of the significance of this crossing: "passing the dividing ridge between the waters of the Columbia and Missouri rivers. From this gap which is low and an easy ascent on the W. side, the fort mountain bears North Eaast, and appears to be distant about 20 Miles." The "fort mountain" he referred to is the prominent Square Butte, a striking volcanic neck rising abruptly from the plains near present-day Great Falls, Montana, a landmark that had first come into view for Lewis during their 1805 ascent of the Missouri River. To see it again from this vantage point confirmed to Lewis that they were indeed returning to known ground.

Square Butte itself is a geological curiosity -- an erosional remnant of basaltic lava flows that solidified during the Miocene epoch, roughly 15 million years ago, when volcanic activity reshaped much of central Montana. Its sheer cliffs and flat summit served as a natural beacon to native peoples and explorers alike, marking a meeting point between mountain and prairie.

Lewis’s group descended the eastern slopes of the pass along Alice Creek, following the trail northwest toward the Missouri River valley. The route was well-marked by generations of hunters who had relied on the bison herds that roamed the plains. The Road to the Buffalo, as it was known, was a vital artery linking the forested highlands with the grasslands, a corridor along which not only people but also plants and animals migrated seasonally.

The journey eastward brought Lewis and his men into the open landscapes of the Great Plains, where the rolling hills were blanketed with bluebunch wheatgrass (Pseudoroegneria spicata) and needle-and-thread grass (Hesperostipa comata). Here the air was alive with the hum of insects and the distant thunder of bison hooves pounding the earth. The plains bison (Bison bison bison) provided sustenance and materials for numerous indigenous tribes -- the very reason the trail was so indispensable.

After weeks of travel, the two factions of the Corps of Discovery reunited on August 12, 1806, near the confluence of the Yellowstone and Missouri rivers, close to the modern city of Williston, North Dakota. The reunion was marked by relief and concern. Clark was startled to learn that Lewis had suffered a serious injury the day before -- a gunshot wound to the right buttock inflicted accidentally by one of his own men, who mistook him for an elk in the dense brush. Despite the pain and the risk of infection, Lewis bore the injury with stoicism. He reflected on the hazards of exploration with characteristic candor, noting, "I have often felt that the dangers of the wilderness were many but the perils from my own party were greater." This admission reveals the constant tension and uncertainty that shadowed the expedition, even as it pushed the boundaries of the known world.

The crossing of Lewis and Clark Pass and the journey along the Road to the Buffalo encapsulate a moment when the expedition reconnected with familiar landmarks -- a geographical and psychological turning point. The pass itself, one of several routes through the Rockies, offered a window into the geological forces that shaped the continent, from Precambrian bedrock to Miocene volcanic outcrops. It also underscored the intimate knowledge indigenous peoples held of this landscape, guiding