Lewis and Clark Trail

By editor

Montana, August 1805

On the morning of August 2, 1805, the Corps of Discovery found themselves camped near the confluence of the North Boulder and Jefferson rivers, in what is today Jefferson County, Montana. The sun rose on a cool dawn, with the thermometer reading fifty degrees Fahrenheit, a crispness that hinted at the approaching elevation and the mountainous terrain that lay ahead. The men, weary from weeks of upstream travel against swift currents, sought both rest and sustenance in the rugged landscape shaped by ancient geological forces.

The Jefferson River, coursing through this segment of the Rocky Mountains, traced its origins to the Three Forks area where the Missouri River begins. The river here is shallow and swift, cutting through sedimentary rocks deposited in the Cretaceous period roughly 70 million years ago. These layers, tilted and folded by the colossal tectonic pressures that built the Rockies, formed steep canyon walls that hemmed in the river’s path. The expedition had been pushing upstream since July 27, straining against the current with heavy dugout canoes, poling and towing with exhausted determination.

Captain William Clark took advantage of the rugged terrain to hunt game for the camp. In a narrow canyon nearby, he shot a bighorn sheep--a species well adapted to the steep, rocky cliffs that characterize this region. The bighorn sheep (Ovis canadensis) is perfectly designed for this broken landscape, their hooves gripping the sheerest precipices. A short distance upstream, Captain Meriwether Lewis successfully shot two pronghorn antelope (Antilocapra americana), fleet-footed creatures of the plains that had wandered into the river valley. This abundance of game offered a much-needed reprieve from the fatigue of constant travel.

The naturalists of the expedition, including the young artist-naturalist John Bradbury and the meticulous botanist William Clark, recorded the flora and fauna with exacting care. Near the camp, they observed a bird previously unknown to Western science, which Lewis later identified as the Maximilian’s jay (Cyanocitta maximiliani). This striking bird, with its bright blue feathers and distinctive crest, would become one of many species that the expedition introduced to the wider world. Lewis wrote with keen observation: "We found the jay in great numbers about the cedars and firs near the river; its note is loud and harsh, and it is fearless of man."

While the men set about their daily tasks, Lewis had departed earlier with a small party on foot, tasked with locating the Shoshone Indians. The expedition’s survival depended upon securing horses from the Shoshone to cross the towering Continental Divide and enter the territory west of the Rockies. The urgency of this mission weighed heavily on Lewis; he knew that without these horses, the journey would be stalled or worse.

The riverbanks bore signs of the harsh environment. The south side of the river revealed the presence of a large brown bear, a formidable creature of the Northern Rockies that inspired both awe and caution among the men. The wilderness here was unyielding and primeval. The expedition’s progress was not without mishap--a man attempting to leap from a canoe onto a rock in the stream broke both ankles. This difficult crossing earned the name Field’s Creek in his honor, a tributary now called the North Boulder River. Such injuries underscored the constant hazard of navigating these waters.

Geologically, the expedition was approaching the Continental Divide, a spine of mountains that separates the watersheds flowing to the Pacific from those draining eastward to the Atlantic and Arctic Oceans. The Rockies had formed over the past 70 million years through the Laramide orogeny, a series of tectonic uplifts and faulting that sculpted the jagged peaks and deep valleys. The men could sense the change in the air and the terrain--the mountains grew larger, their snow-capped summits piercing the sky above the dense coniferous forests of firs, pines, and cedars.

One of the notable landmarks near the expedition’s route was the “Little Gates of the Mountains,” a series of cliffs on either side of the Missouri River described to Lewis and Clark by Indian informants at Fort Mandan in present-day North Dakota. These cliffs marked the approach to the second chain of the Rocky Mountains, where the river carved a narrow passage through imposing rock faces. About 60 miles downstream lay the more famous “Gate of the Rocky Mountains,” a natural portal through the mountains that the expedition would encounter in the coming weeks.

During their passage near present-day Toston, Montana, on July 25, 1805, the expedition camped on the west side of the Missouri River just upstream from what is now Toston Dam. It was here that Meriwether Lewis made a noteworthy botanical discovery--the Stipa comata, commonly called Needle and Thread grass. Lewis carefully described this species, noting its long, slender awns that twist and coil with changes in humidity--a remarkable adaptation for seed dispersal in the dry grasslands that fringe the river valleys. The discovery of such species contributed to the expedition’s broader scientific mission, cataloging the vast biodiversity of the western continent.

Clark also mapped a large spring near this location, which remains visible today about half a mile below the dam. Springs such as this one were critical in the arid regions of Montana, providing reliable water sources for both indigenous peoples and travelers. The expedition’s meticulous records of these natural features reflected their reliance on precise navigation and understanding of the landscape.

The men’s journey through Montana was a gradual transition from the rolling plains into the complex, rugged terrain of the Rocky Mountains. The geological formations they encountered--limestone cliffs, sandstone layers, and igneous intrusions--told a story of ancient seas, volcanic activity, and the slow but relentless uplift that shaped the continent. The river valleys they followed had been carved over millennia by the ceaseless flow of water, creating narrow canyons and broad floodplains that sustained diverse ecosystems.

In the words of William Clark, writing in his journal on August 2, “The river is becoming more rapid and the valley narrower; the mountains rise abruptly on either side, their peaks crowned with snow, challenging our passage westward.” This passage reveals the growing awareness among the men of the formidable natural barrier ahead, yet also their resolve to continue.

The Lewis and Clark Expedition’s passage through Montana was not merely a journey of geographic discovery but also an unfolding scientific inquiry into the continent’s natural history. Their detailed observations of geology, flora, fauna, and indigenous cultures laid the groundwork for the mapping and understanding of the American West. The men’s struggles and triumphs along the Jefferson River and its tributaries capture a moment when the vast interior of the continent was still a mystery, waiting to be recorded with precision and care.

As the expedition pressed onward, the Continental Divide awaited, and beyond it, the vast Pacific watershed. The mountains loomed closer, their ancient stones bearing silent witness to the relentless march of time and the passage of men who sought to know them.

See also

• Lewis and Clark Trail at Fort Benton, Chouteau County
• [Lewis and Clark Reach the Headwaters](/historic-markers/lewis-and-clark-re