South of Hamilton, the serrated peaks and forested foothills of the Bitterroot Mountains close in along US-93 as the valley narrows sharply, the towns shrink in size, and woodlands (and campgrounds) replace farmlands (and commerce) along the roadside. Just 17 miles south of Hamilton, the pioneer village of Darby has a couple of cafés, a log-cabin public library, and an only-in-Montana combination: a liquor store that sells secondhand books and used fishing flies. Darby also has a helpful ranger station (406/821-3913), the best source of information on hiking and camping in the Bitterroots.

  South of Darby, US-93 cuts away from the Bitterroot River at the hamlet of Sula, beyond which the highway continues its slow climb up through seven miles of sub-alpine landscape to another of Montana’s many pleasant resorts, Lost Trail Hot Springs (406/821-3574 or 800/825-3574), at 8321 Hwy-93 South, open year-round with hot springs pools ($6), an attractive variety of moderately priced rooms and cabins, and good on-site restaurant. Lost Trail is especially popular with cross-country skiers, who can traverse many miles of nearby trails, including the route followed by Chief Joseph and the Nez Percé in 1877 while fleeing from the U.S. Cavalry.

  From Lost Trail Hot Springs, US-93 climbs up to 6,995-foot Lost Trail Pass, which Lewis and Clark crossed in 1805 on their return from the impassable Snake River, and which now marks the border with Idaho. The pass also serves as a low-key downhill ski area ($24; 406/821-3211), with 1,200 vertical feet of groomed runs.