Where Did Lewis And Clark Cross The Rocky Mountains: Historic Routes And Modern Trail Guide (2026 Edition)

The crossing of the Rocky Mountains by the Corps of Discovery between 1805 and 1806 remains one of the most perilous, physically demanding mountain transits in recorded North American exploration. Commissioned by President Thomas Jefferson to map the newly acquired Louisiana Territory and chart a navigable water route to the Pacific Ocean, Meriwether Lewis and William Clark did not cross the Rocky Mountain cordillera in a single mountain pass. Instead, they navigated multiple distinct mountain ranges, continental divides, and high-altitude traverses across modern-day Montana and Idaho.

Understanding exactly where Lewis and Clark crossed the Rocky Mountains requires examining two distinct phases of their expedition: their grueling westward transit in late summer and autumn of 1805, and their split return journeys across the northern and southern passes in the summer of 1806.

The Primary Mountain Crossings: Geographic Coordinates and Historic Timeline

The Rocky Mountain transit stretched across hundreds of miles of rugged wilderness, primarily through the Beaverhead Mountains and the Bitterroot Range. The expedition relied extensively on the geographical intelligence and physical guidance of Shoshone guides (notably Cameahwait's people and the guide Old Toby) and later the Nimíipuu (Nez Perce) people.

1. Lemhi Pass: Traversing the Continental Divide (August 12, 1805)

Meriwether Lewis, scouting ahead of the main party with a small advance detachment, became the first recorded American citizen to reach the crest of the Continental Divide at Lemhi Pass on August 12, 1805.

• Location: Border of Beaverhead County, Montana, and Lemhi County, Idaho (Beaverhead Mountains).
• Elevation: 7,373 feet (2,247 meters).
• Significance: At this point, Lewis famously drank from what he believed to be the ultimate headwaters of the Missouri River (specifically Trail Creek, feeding the Beaverhead and Jefferson rivers), stepped across the crest, and looked westward expecting to see plains and navigable waters. Instead, he confronted endless tiers of snow-capped peaks: the Salmon River Mountains and the Bitterroots.

Field Note from the Continental Divide

On August 12, 1805, Meriwether Lewis ascended to the ridge of the dividing mountain which will serve as the natural boundary between the waters of the Atlantic and Pacific oceans. Here, the long-held eighteenth-century geographic myth of an easy commercial water passage—the Northwest Passage—evaporated against the reality of the Northern Rockies.

2. Lost Trail Pass: Descent into the Bitterroot Valley (September 3–4, 1805)

After trading with the Shoshone for pack horses and determining that the Salmon River canyon was entirely impassable for watercraft ("The River of No Return"), the Corps diverted north under the guidance of the Shoshone guide Swooping Eagle (referred to in the journals as Old Toby).

• Location: Border of modern Ravalli County, Montana, and Lemhi County, Idaho.
• Elevation: 7,014 feet (2,138 meters).
• Significance: The expedition struggled through steep, timber-choked ravines, navigating deep snow and slick scree slopes to cross back into Montana, emerging into the Bitterroot Valley near modern-day Sula and Hamilton.

3. Lolo Pass and the Lolo Trail: The Bitterroot Mountain Ordeal (September 11–22, 1805)

The single most grueling alpine trial of the entire expedition occurred along the Lolo Trail, an ancient Nez Perce highway (K'useyneiskit) traversing the crest of the Bitterroot Range.

• Location: Border of Missoula County, Montana, and Clearwater/Idaho counties, Idaho.
• Elevation: 5,233 feet (1,595 meters) at the saddle of Lolo Pass; trail ridges along the high mountain route exceeded 7,000 feet.
• Significance: Early winter storms deposited knee-deep snow across the ridgelines. With game nonexistent in the high timber, the party suffered from acute hypothermia and near-starvation. To survive, the men killed several of their own colts for nourishment ("Colt Creek") before emerging, emaciated and critically weakened, onto the Weippe Prairie of Idaho, where they were saved by the Nez Perce.

4. Lewis and Clark Pass: The Eastbound Shortcut (July 7, 1806)

On their return trip from the Pacific, the expedition divided forces at Travelers' Rest (near Lolo, Montana) to explore divergent routes. Meriwether Lewis led a party of nine men directly eastward along a route recommended by Nez Perce guides, known historically as the "Road to the Buffalo."

• Location: Lewis and Clark County, Montana, near the town of Lincoln.
• Elevation: 6,000 feet (1,829 meters).
• Significance: Lewis crossed the Continental Divide via this distinct pass, which proved vastly superior and faster than the southern detour taken in 1805. Lewis and Clark Pass remains one of the few places along the entire National Historic Trail that is non-motorized and accessible solely on foot or horseback.

5. Bozeman Pass and Gibbons Pass: Clark's Southern Return (July 1806)

While Lewis probed the northern passage, William Clark took another party south through the Bitterroot Valley, crossing Gibbons Pass (elev. 6,941 ft) into the Big Hole Basin. Clark then crossed the Continental Divide, moved across the Gallatin Valley guided by Sacagawea, and crossed Bozeman Pass (elev. 5,712 ft) to reach the headwaters of the Yellowstone River.

Technical Comparison of Rocky Mountain Passes Used by the Expedition

Key Strategic Challenges Faced During the Mountain Crossings

Crossing the Northern Rockies tested the operational resilience of the expedition to its absolute limits. Several geographic, physiological, and logistical realities dictated their route:

The Collapse of the "Pyramid Height of Land" Theory

Eighteenth-century European and American geographers operated under the mistaken belief of symmetric continent geography: that the Rockies were a narrow, uniform ridge similar to the Blue Ridge or Alleghenies, with rivers flowing smoothly down opposite slopes from a single high point. When Lewis crossed Lemhi Pass, he discovered that instead of a simple portage of a few miles, hundreds of miles of alpine wilderness separated the navigable waters of the Missouri from the Columbia basin.

Navigational Dead Ends: The Salmon River Canyon

Clark attempted to find a water route down the Salmon River after crossing Lemhi Pass into Idaho. Local Shoshone leaders warned him the river flowed through a vertical canyon of boiling rapids that no canoe could survive. After personally scouting 20 miles of the churning gorge near modern-day North Fork, Clark confirmed the warnings, forcing the expedition to abandon their canoes, buy pack horses, and swing far north over high, snow-bound mountain passes.

Logistical Starvation on the Lolo Trail

Because the high ridges of the Bitterroots supported thick cedar, fir, and hemlock canopies with minimal ground browse, big game such as deer, elk, and bison were virtually nonexistent along the crests. The expedition exhausted their salt pork and portable soup, faced freezing conditions without cold-weather footwear, and were forced to eat portable survival rations, roots, and eventually horses.

Modern Traveler & Heritage Guide: Visiting the Crossings in 2026

For historians, overland travelers, and outdoor enthusiasts tracing the Lewis and Clark National Historic Trail, these mountain crossing points offer extraordinary preserved landscapes.

Visiting Lemhi Pass

• Access Route: Accessible from Tendoy, Idaho, via Agency Creek Road (dirt and rough gravel), or from Dillon, Montana, via Highway 278 and Lemhi Pass Road.
• Road Conditions: Single-lane gravel with steep grades; strictly dry-weather seasonal travel (typically late June through October). High-clearance vehicles are recommended.
• Key Landmark: The Sacajawea Memorial Camp, historical markers, and the spring that forms the ultimate source of the Missouri River.

Navigating Lolo Pass & Highway 12

• Access Route: Traversable along U.S. Highway 12, running between Lolo, Montana, and Lewiston, Idaho, through the Clearwater National Forest.
• Visitor Amenities: The Lolo Pass Visitor Center (at the summit) features deep interpretations of both the Lewis and Clark Expedition and the 1877 Nez Perce Flight.
• Trail Conditions: The primitive, unpaved Lolo Motorway (Forest Service Road 500) parallels the true crest trail for off-road vehicles during mid-to-late summer, preserving original tread marks from centuries of Indigenous travel.

Hiking Lewis and Clark Pass

• Access Route: Located north of Lincoln, Montana, via Alice Creek Road (FS Road 293).
• Trail Profile: A moderate non-motorized trail ascends roughly 1.5 miles from the trailhead to the summit pass (approx. 1,000-foot elevation gain).
• Preservation Status: This is the most pristine, roadless mountain crossing of the entire 1804–1806 journey. Hikers can stand directly in the stone-bordered entrenchments worn into the mountain saddle by Indigenous buffalo-hunting parties and Lewis's returning contingent.

Frequently Asked Questions

Did Lewis and Clark find a continuous water route through the Rocky Mountains?

No. Lewis and Clark decisively proved that no navigable, continuous water passage (the legendary Northwest Passage) exists across the Rocky Mountains. Instead, traversing the Rockies required a grueling overland portage of more than 300 miles of alpine terrain between the headwaters of the Missouri and the navigable tributaries of the Columbia River (the Clearwater and Snake rivers).

What was the highest elevation Lewis and Clark reached while crossing the Rockies?

The highest recorded pass the main expedition crossed was Lemhi Pass at 7,373 feet (2,247 meters), along the Beaverhead Mountains on the Continental Divide. However, during their traverse of the high ridgelines along the Lolo Trail, expedition parties regularly operated at elevations ranging between 7,000 and 7,500 feet along exposed alpine ridges to avoid impenetrable, choked valley bottoms.

Which Native American tribes assisted the expedition through the mountains?

The Shoshone, under Chief Cameahwait (Sacagawea's brother), provided critical horses, pack gear, and the primary guide Old Toby to negotiate the Salmon and Bitterroot divides. Additionally, the Salish (Flathead) at Ross's Hole provided aid, and the Nimíipuu (Nez Perce) on the Weippe Prairie rescued the freezing, starving men after their descent from the Lolo Trail, keeping their horses and canoes safe during the winter.

What is the difference between Lemhi Pass and Lolo Pass?

Lemhi Pass crosses the Continental Divide between Montana and Idaho, marking where the expedition first realized that the Rocky Mountains were an extensive mountain system rather than a single ridge. Lolo Pass, located further north, crosses the Bitterroot Range and served as the direct east-west conduit connecting the Bitterroot Valley to the Pacific Northwest drainage via the historic Nez Perce Trail.

Can you drive across the passes Lewis and Clark used today?

Yes, several passes are completely modernized, while others remain primitive. Lolo Pass (U.S. Highway 12) and Lost Trail Pass (U.S. Highway 93) are paved, year-round highways. Lemhi Pass and Gibbons Pass remain unpaved, seasonal dirt roads accessible primarily in summer. Lewis and Clark Pass is located within protected federal forest lands and is accessible only by foot or horseback.

Charting Your Heritage Expedition

Tracing the paths carved by the Corps of Discovery provides an unmatched window into the physical geography of the American West. When planning your route across the Northern Rockies, plan according to current seasonal conditions: alpine passes across the Bitterroots and Beaverheads often remain snowbound well into late June. Verify road statuses with the U.S. Forest Service before departing, ensure your vehicle is equipped for unpaved logging corridors, and respect the cultural sovereignty of the tribal lands that made the original 1805 crossing possible.