The Lewis and Clark Expedition

By editor

Dillon, Beaverhead County, Montana

In the spring of 1804, a company of roughly forty men, comprised of soldiers, boatmen, and frontiersmen, embarked on a journey from Camp Dubois near St. Louis, Missouri. Commanded by Captains Meriwether Lewis and William Clark, this Corps of Discovery was commissioned by President Thomas Jefferson to explore the vast Louisiana Territory newly acquired through the Louisiana Purchase. Their mission was to chart a water route to the Pacific Ocean, gather scientific data on the region’s flora, fauna, and geology, and establish relationships with Indigenous nations along the way.

Jefferson’s instructions to Lewis were notably rigorous and comprehensive. He wrote that Lewis was to “endeavor to discover the course and termination of the Missouri, and such principal stream of it, as, by its course and communication with the waters of the Pacific Ocean, whether the Columbia, Oregan, Colorado or any other river may offer the most direct and practicable water communication across this continent.” Alongside cartographic duties, Lewis was charged with collecting specimens of plants and animals, recording observations on the land’s natural resources, and negotiating peaceable interactions with native peoples. Thus, Lewis took on the roles of scientist, diplomat, and soldier simultaneously.

The expedition’s first winter was spent at Fort Mandan, near present-day Washburn, North Dakota. Here, they encountered the French-Canadian fur trapper Toussaint Charbonneau and his young Shoshone wife, Sacagawea. She became indispensable as an interpreter and guide. As they resumed their westward journey in early 1805, the Corps pushed into territories unmapped and unknown to any American.

By late July of 1805, the expedition arrived at the confluence of three rivers in what is now Montana -- the junction that forms the Missouri River’s headwaters. Lewis named these the Jefferson, Madison, and Gallatin, honoring three of President Jefferson’s close political allies. The Jefferson River, which they followed upstream, carves through the geologically complex landscape of the Beaverhead region. The valley walls here reveal strata from the Precambrian Belt Supergroup, rocks aged between 1.4 and 1.5 billion years, layered with quartzites, argillites, and carbonate beds that tell of ancient marine environments and mountain-building episodes.

The men faced considerable hardships as they dragged their canoes over gravel bars in waters so shallow they barely floated the vessels. Their progress was slow and exhausting. The Bitterroot Mountains loomed ahead -- a rugged spine of crystalline granite and gneiss metamorphosed over eons by tectonic forces. The peaks rise sharply, shaped by glacial sculpting during the Pleistocene epoch. It was a landscape that had remained largely unchanged since the last great ice retreat, save for the footprints of the Native peoples who had hunted and traversed here for centuries.

At a prominent outcrop known as Beaverhead Rock, the expedition’s Shoshone interpreter, Sacagawea, recognized her homeland for the first time since she had been taken captive years earlier. The rock itself is a massive cliff of quartzite, standing over 900 feet above the river, its sheer face worn smooth by wind and water erosion. This moment was pivotal. At the nearby Camp Fortunate, the explorers were reunited with Sacagawea’s brother, the Shoshone chief Cameahwait. The Shoshone provided horses and a guide named Old Toby, a Nez Perce scout familiar with the mountain passes.

The journey over the Bitterroot Mountains was arduous. Old Toby led the party along the Lolo Trail, a narrow, ancient footpath winding through steep valleys and dense forests of western red cedar (Thuja plicata) and Douglas fir (Pseudotsuga menziesii). The men battled heavy snowdrifts and bitter cold. Clark later wrote of the ordeal: “The mountains are very steep and high, and covered with snow which makes traveling very difficult.” This passage was the last major obstacle before reaching the Columbia River basin.

After crossing the mountains, the expedition descended into the vast and fertile valleys of present-day Idaho and Washington. They followed the Columbia River westward, finally arriving at the Pacific Ocean on November 15, 1805, at a place they named Fort Clatsop, near modern Astoria, Oregon. This point marked the culmination of a 2,700-mile journey through terrain that ranged from prairie grasslands to alpine forests and arid badlands.

The Corps of Discovery returned east in 1806, retracing much of their route but with additional knowledge of the terrain and native nations. Their records, maps, and collections filled volumes and laid the groundwork for future American exploration and settlement.

The landscape around Beaverhead County has altered since Lewis and Clark passed through. The Missouri River’s flow has been regulated by dams like the Canyon Ferry and Holter Dams downstream. The once-continuous forests have been logged extensively, replaced in places by ranchlands and croplands. Roads and highways cut across valleys where the expedition once portaged their canoes. Yet the mountains themselves remain -- the same ancient, rugged summits shaped by Precambrian geology, the same valleys carved by glacial ice and riverine erosion. The rivers continue to run in their original channels, and the trail the explorers followed lies beneath the surface, marked by their campsites and journals.

Meriwether Lewis remarked upon the richness of this land’s natural resources: “The country through which we have lately passed may be called the garden of the continent.” His words reveal not only the abundance of game such as bighorn sheep (Ovis canadensis), elk (Cervus canadensis), and mule deer (Odocoileus hemionus), but also the diversity of plant life including bitterroot (Lewisia rediviva), the state flower of Montana, which blooms in these dry grasslands.

Their observations extended to the geology as well. Lewis and Clark noted the striking cliffs, the “immense precipices of rock,” and the “fountains of mineral water” that rose along the riverbanks. These early descriptions provide a snapshot of Montana’s wilderness before industrialization.

Sacagawea’s presence on the expedition was vital beyond her linguistic skills. Her knowledge of the terrain and native cultures helped the Corps navigate political and environmental challenges. Clark wrote in his journal: “Sacagawea, the young woman of the Shoshone nation, has been an invaluable guide and companion to us, her familiarity with the land and peoples is a blessing.”

As one stands today at Beaverhead Rock or Camp Fortunate, it is possible to imagine the expedition’s men confronting the same winds, the same towering cliffs, and the same river currents that Lewis and Clark described over two centuries ago. The land invites us to observe the layers of deep time and human endeavor etched into its surfaces.

See also

• The Lewis and Clark Expedition at Dillon, Beaverhead County (National Park Service)
• Camp Fortunate at Dillon, Beaverhead County
• Beaverhead Rock at Dillon, Beaverhead County