In 1805 Lewis and Clark crossed the divide between Lemhi County (Idaho) and Ravalli County (Montana) approximately northwest of Lost Trail Pass to enter the Bitterroot Valley on September 4. They later rested for a few days at Travelers' Rest, near present-day Lolo, in preparation for their crossing over the snowy Bitterroots at Lolo Pass, back into present-day Idaho, following the Lolo Trail, north of US-12.