The D&RGW K-37 class represented the largest narrow-gauge steam locomotives constructed for the Rio Grande system.
Unlike the K-28 and K-36 classes, the K-37s were not ordered as entirely new locomotives from ALCO or Baldwin.
The railroad reused major components from retired standard-gauge locomotives.
Stearns-Roger Manufacturing Company and D&RGW’s Burnham Shops produced new frames, wheels, axles, and other narrow-gauge running gear.
The rebuilt locomotives entered service around the end of the 1920s.
Their greater weight and tractive effort made them useful on heavy freight assignments but also limited where they could operate because bridges and track had to support the heavier axle loading.
K-37s became closely associated with the final decades of Rio Grande freight work in southwestern Colorado and northern New Mexico.
Several survived preservation, including No. 491 at the Colorado Railroad Museum and No. 493 on the Durango & Silverton.
The survival of multiple examples allows historians to compare coal-fired museum operation, oil-fired tourist operation, and static preservation.
For TransitSatellite, the K-37 story should emphasize reconstruction. Calling them simply “built in 1928” without mentioning the reused standard-gauge boilers hides the engineering process that makes the class distinctive.