The K-36s were used primarily as freight locomotives out of Alamosa to Durango, and to Farmington, New Mexico, as well as out of Salida to Gunnison (over Marshall Pass) until 1955 and to Monarch on the Monarch Branch until 1956. They were built with special valves to allow brake control between locomotives while double-heading, and were commonly found between Alamosa, Colorado and Chama, New Mexico. They were heavily used during the pipe boom in Farmington, and hauled long freight trains between Alamosa and Farmington.