The locos worked out of Salida, Colorado to Gunnison, Colorado and up the Crested Butte Branch as well as the Monarch Branch. The locos also worked out of Alamosa, Colorado to Antonito over Cumbres Pass to Chama and on to Durango and the Farmington branch. Like the K-36s the locos were not permitted West of Gunnison or on the Silverton branch. However, the Silverton branch has since been upgraded the track and line to handle K-36s and K-37s. 3 of the K-37s, Nos. 493, 491 and 499, were equipped with steam heat and signal lines so they could haul passenger trains like the San Juan Express and Shavano.