Lt. Mullan was a West Point graduate who came west in 1853 as part of the railroad survey of Governor Isaac Stevens (1818-1862). He spent a season or two searching for a practical route through the Rocky Mountains. Then in the mid-1850s hostilities with the Indians broke out and in 1858 Lt. Mullan attached himself to the bloody retaliatory expedition of Col. George Wright. When that was over, Lt. Mullan went back to his project of building a road.
The Mullan Road helped Walla Walla to grow to the largest town in Washington Territory by 1870, with a population of 1,394. Walla Walla merchants catered to miners with gold fever and to farmers. Ferries on the Snake River tried to make their landings convenient to the road.
Parts of the old Mullan Road are still (in 2005) in use (for example, off State Route 26 about three miles east of Washtucna).