Lost Trail Pass

Lost Trail Pass sits at 7,014 ft on the Montana and Idaho state line, where U.S. Highway 93 crosses the Bitterroot Mountains (Wikipedia). It is a Bitterroot Divide crossing, not a Continental Divide crossing. The Divide itself runs about a half mile east of the summit, back inside Montana. At the top you hit a three-way junction: US-93 runs north and south, and MT-43 peels off east toward Chief Joseph Pass and Gibbons Pass. The Lost Trail Powder Mountain ski area sits right at that junction, which tells you most of what you need to know about the snow up here.

North of the summit, US-93 drops into the Bitterroot River Valley and runs toward Sula, Darby, Hamilton, Lolo, and on to Missoula. Sula is roughly 13 miles down the Montana side. South, the road descends into Idaho toward North Fork, where the Salmon River turns west, then on to Salmon. This is the main link between the Bitterroot Valley and the Salmon River country, and there is no easy parallel route to take instead.

For a driver, the concerns are straightforward. It is a high two-lane mountain crossing with sustained grades on both approaches and a hard seasonal climate. The Idaho side ices and closes faster than the Montana side. A single jackknifed semi can block both directions until it is cleared. Sources describe roughly 5 miles of climbing on each approach, but the exact grade figures circulating online are not DOT-verified, so plan for a real climb and check live conditions before you start it.

• Summit elevation is 7,014 ft on the Montana and Idaho state line in the Bitterroot Mountains (Wikipedia); dangerousroads.org lists a slightly higher 7,030 ft.
• Carried by US-93; Ravalli County, MT on the north side, Lemhi County, ID on the south.
• The summit is about a half mile west of the Continental Divide, so this is a Bitterroot Divide crossing, not a Continental Divide one (Wikipedia).
• At the top, MT-43 junctions east toward Chief Joseph Pass and Gibbons Pass; the ski area sits at this junction.
• Sula, MT is roughly 13 miles north of the summit; the south side descends to North Fork and Salmon, Idaho.
• Not on MDT's seasonally closed roads list, so it stays open and maintained year-round (MDT Seasonally Closed Roads).
• Sources describe roughly 5 miles of climbing on each approach, but no DOT-verified grade percentage exists.

There is no fixed chain-control season or closure date here, because US-93 over Lost Trail Pass stays open and maintained year-round. It does not appear on MDT's seasonally closed roads list, which covers only Beartooth, Skalkaho, Looking Glass, and Thompson Pass (MDT Seasonally Closed Roads). What does run on a calendar is Idaho's commercial chain-up law. On the Idaho side, chains can be required on commercial vehicles over 26,000 lb when ITD activates roadside chain-up signs, and the enforcement window runs October 1 through April 30 under Idaho Code 49-948. The requirement comes off as soon as conditions allow. Montana does not run a posted chain-level system like California's R-1, R-2, R-3; MDT handles it through live conditions and any traction or closure orders on its 511 system. Closures here are short and incident-driven, triggered by ice, freezing rain, crashes, or storms, and the road reopens once it is cleared. Check Idaho 511 and MDT 511 before you climb.

In early September 1805, the Lewis and Clark expedition crossed the Bitterroot Divide near present-day Lost Trail Pass. The going was brutal on September 3, with several of their roughly 29 horses falling or getting injured on the terrain. On September 4, guided by Old Toby, the Corps descended into Ross's Hole and met a large Salish encampment. Wikipedia places the actual crossing about 1.3 miles northwest of today's pass. The name came later. According to local and Lewis and Clark histories, highway surveyors laying out the route around 1910 got temporarily confused about their location, and the "Lost Trail" name was attached when the highway gap was named, reportedly at the urging of a local rancher who knew the expedition journals. By most accounts, construction of US-93 began piecemeal in the mid-1920s and the route over the gap was completed and named in the 1930s.

The pass still closes on short notice in bad weather. On December 27, 2022, US-93 briefly closed on the Idaho side because of freezing rain, with MDT reporting hazardous, severe driving conditions that morning (NBC Montana). In March 2026, a jackknifed semi blocked both lanes at the pass and shut the highway until it was cleared and reopened (Ravalli Republic).