From 1858-62, Lt. John Mullan's crew built the Northwest's first engineered highway, connecting Fort Benton with Fort Walla Walla for 625 miles. In Idaho, I-90 closely follows the original road. Mullan's crew spent July 4, 1861 here and carved the date into a white pine, creating the famous Mullan Tree. The diseased tree, the last Mullan Road marker, was removed in 1988.