In 1824, while searching the mountain wilderness of what is presentday Idaho, known to them as Columbia District, for beaver, Alexander Ross came up the Wood River and discovered Galena Summit on September 18. Leading a large brigade of Hudson's Bay Company trappers, he wondered if he could get through unknown mountains and rocky defiles that obstructed his passage back to his base of operations at present Challis. Unwilling to turn back he pressed on to explore Stanley Basin and the difficult canyon beyond. When he reached Challis on October 5, 1824, he had traveled the route now followed by Idaho State Highway 75 from Bellevue to Salmon through mostly unexplored land. The road itself dates back to at least 1926, when it was designated U.S. Route 93. The former U.S. Route 93 Alternate, running through Arco, was redesignated as U.S. Route 93 in 1977, and at that time this route was given its current state highway designation.