In April 1846, Miller was engaged by George Donner to drive his wagons west to California. At Fort Laramie in July, Miller and some other single men left the main group and continued separately for California, reaching Sacramento quickly and safely. Miller returned several times on foot to the party's camp in the Sierra Nevada mountains to take supplies to the stranded emigrants, and eventually rescued two of the orphaned Donner children out of the mountains. He settled in California.
John Carroll Power and S. A. Power, History of the Early Settlers of Sangamon County, Illinois (Springfield, IL: Edwin A. Wilson, 1876) 601; Eliza Poor Donner Houghton, The Expedition of the Donner Party and Its Tragic Fate (Chicago: A. C. McClurg, 1911), 30, 119, 124-25.