Denver & Rio Grande Western No. 491 is a K-37 narrow-gauge 2-8-2 completed in 1928 through work by the D&RGW Burnham Shops and Stearns-Roger Manufacturing Company in Denver.
The K-37 class was not built as entirely new locomotives in the usual sense. The Rio Grande reused major components from retired standard-gauge locomotives, including boilers, cabs, and tenders.
New narrow-gauge frames, wheels, axles, and related running gear were fabricated to create locomotives able to work on three-foot-gauge track.
This rebuilding strategy allowed the railroad to obtain more powerful narrow-gauge locomotives without purchasing a completely new fleet from an outside builder.
No. 491 worked in D&RGW service until the early 1960s.
The locomotive was preserved rather than scrapped and eventually came under the care of the Colorado Railroad Museum.
In 2013 the museum received ownership of No. 491 from History Colorado after years of display and loan arrangements.
The locomotive returned to operating service in August 2014 after museum restoration work.
The museum currently uses 491 for special events and interprets it as one of the largest operating coal-fired narrow-gauge steam locomotives in North America.
For TransitSatellite, No. 491 should be shown as a rebuilt locomotive with a dual technological lineage: standard-gauge boiler-era components combined with purpose-built narrow-gauge running gear.