In early 1858, Simpson was ordered to join the Army's reinforcements for the Utah War. He and his team resurveyed the trails from Fort Leavenworth to Utah and his photographer, Samuel C. Mills, produced the earliest surviving photographs of features along the trail. Upon his arrival at Camp Floyd, he was directed to open a new road between that post and Fort Bridger. Simpson and his team also surveyed the military reservation at Fort Bridger, at Camp Floyd and in the Rush Valley. In May 1859, he headed an expedition to survey a new route from Camp Floyd  across the Great Salt Lake Desert of Utah and through the Great Basin to Genoa, Nevada near California. The Army contracted Frederick Lander to immediately to develop the more direct route to California for use by wagons, and Simpson's survey was later published in 1876. Simpson's Central Route played a vital role in the transportation of mail, freight, and passengers between the established eastern states and California, especially when hostilities of the Civil War closed the Butterfield Overland Mail stagecoach route that ran along the southern border states. George Chorpenning immediately switched to Simpson's route to run his existing mail and stage line, and the Pony Express used it as well. In 1861 the Transcontinental Telegraph was laid along the route, making the Pony Express obsolete. Afterwards, Wells Fargo & Co. hauled mail, freight, and passengers along Simpson's route until 1869, when transportation and telegraphy were switched to the newly completed Transcontinental Railroad.. How many years after Simpson began resurveying trails from Fort Leavenworth to Utah did Wells Fargo & Co. haul mail, freight, and passengers along his route?