Along with Bannock pass, located about fourteen miles farther south, Lemhi pass provides access across the continental divide from the upper Missouri to the upper Salmon. When the Lemhi Shoshoni acquired horses in the eighteenth century, Lemhi pass gained importance as a route connecting the two major parts of their homeland (Lemhi valley and Bighole, along with adjacent parts of the upper Missouri) as they traveled about in an annual migratory cycle which featured salmon fishing to the west and buffalo hunting farther east. After mounted Blackfeet began to range farther south and west on horses, they regularly used Lemhi pass to reach the upper Snake, so that by 1824, Alexander Ross referred to the Lemhi pass route as the Blackfoot road. From the time of the Louisiana purchase in 1803, Lemhi pass was on the new nation's western boundary. Since 1846, aside from slightly over a year in 1863-1864, it has been on a territorial or state boundary.
For Lewis and Clark, Lemhi pass represented a major objective, and when four members of the expedition crossed there August 12, 1805, Lewis finally had achieved his goal of reaching Columbia river drainage. He soon found a Lemhi Shoshoni camp west of the divide, and the expedition was able to proceed on north to the Lolo trail.
After Lewis and Clark, North West Company and Hudson's bay Company fur brigades came through Lemhi pass to reach the Snake country, and Finnan MacDonald fought an important battle with the Blackfeet in a defile on the regular trail a few miles west of the pass in 1823. Jedediah Smith brought mountain men based in St. Louis to the Snake country in 1824, but used South pass (named in distinction from North pass--as they referred to Lemhi pass--of Lewis and Clark) rather than Lemhi pass for regular access to the fur empire. During the fur trade era, Hudson's Bay Company officials wanted to use Lemhi pass as the point of origin on the continental divide for an Oregon country boundary between Britain and the United States (with the area north and west of Lemhi pass going to Great Britain, and the rest to the United States), but this arrangement never was accepted.
During the mining era, stage service from Montana to Salmon used Lemhi pass. After 1910, when the Gilmore and Pittsburgh railway began to serve Salmon through Bannock pass, Lemhi pass fell into disuse. Bannock pass also became the highway route for traffic across that part of the continental divide, and Lemhi pass wound up with a single lane dirt road to accommodate visitors to this significant historic landmark.