The idea of a wagon road through Sonora Pass connecting Tuolumne County with the mining towns of Mono County was first brought forward by Andrew Fletcher in 1862. The original trail through Sonora Pass was opened for pack animals in September 1862. It crossed this divide, left the route of the present highway one mile west, climbed northwesterly through St. Mary’s Pass at an elevation of 10,040 feet, and then descended the canyon of the Clark Fork of the Stanislaus River. In 1863 the route was resurveyed and relocated from Sonora Pass down Deadman Creek and the Middle Fork of the Stanislaus River. The wagon road that established the general location of the present highway was completed through the pass in 1865.