It sits on the Continental Divide on the border between Powell and Lewis and Clark counties at 5,902 feet (1,799 m) above sea level.

The NP also built an alternate line over Homestake Pass, which was used by their primary passenger train, the North Coast Limited.

On September 30, 1911 Mullan Pass was the site of the first aeronautical crossing of the North American Continental Divide.

An explosion later linked to a tank car filled with hydrogen peroxide shook the town, knocked out power, and caused extensive damage in the community, but no deaths.

[2] In mid-July 2009, part of the Mullan Tunnel roof collapsed while it was being enlarged to handle double-stack freight cars.