This branch was a remnant of an earlier line that extended from Benson (on SP's Sunset Route) to Nogales, on the Arizona border with Mexico. It passed through remote country, serving military forts and mines in the area. Heading west from Fairbank, the branch line passed through Brookline, Huachuca City, Ballybrophy, Landers, Elgin, Canelo, Sonoita, Ashburn, Casa Blanca and (Fort) Crittenden to Patagonia. In later years (1930s) only the Fairbank to Patagonia segment remained in service, and this was later cut back and then abandoned. The eastern portion of the branch does not pass near many paved roads, and the old grade can be located near the Babocomari River. Further west the line paralleled Ariz. Route 82 between Sonoita and Patagonia. This branch was several miles north of, and not connected to, the SP Fort Huachuca Branch.