From this point west to the Idaho line, U.S. Highway 12 and I-90 follow the route of a military road located and constructed in Montana between 1859 and 1862 by Captain John Mullan. The 624-mile road connected Fort Benton, Montana, with Fort Walla Walla, Washington. Originally an Indian trail, the route was mapped by Mullan over the pass in the 1850s and in 1860 was incorporated into the military road that bore his name. In his final report, Mullan predicted that locomotive engines would make passage through the wild interior at startling speeds. Two decades later, in 1883, the Northern Pacific Railway built its main line over Mullan Pass. An unusual freight crossing had come earlier, in 1865, when seven camels, each carrying 600 pounds of flour, traveled from Helena to the Deer Lodge area mines. Although the dromedaries could carry tremendous loads, were sure-footed, and had great stamina, they alarmed the horses, mules, and oxen of teamsters and mule packers, and the camels were gone from Montana by 1867.