This branch is a remnant of the former mainline of the New Mexico and Arizona Railroad, built in 1882, 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. In later years (1930s) only the segment between Fairbank and 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 AZ Route 82 between Sonoita and Patagonia. This branch was several miles north of, and not connected to, the Southern Pacific's Fort Huachuca Branch.
Heading west from Fairbank, the branch line passed through these towns/stations:
- Huachuca City
- Casa Blanca
- (Fort) Crittenden