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Rio Grande 4-6-6-4 Locomotives: Specs, Roster, Photos

Published: April 10, 2025

By: Adam Burns

The Rio Grande was always after large and powerful locomotives to handle heavy freights through the rugged Colorado Rockies, in particular with its ever-constant battle of Tennessee Pass.  It utilized wheel arrangements such as the 2-8-8-2, 2-6-6-2, 2-10-2, 4-8-2, and 4-8-4.

The railroad acquired its first examples of the 4-6-6-4 in 1938 from Baldwin and later picked up more a few years later.  The company's intent was to speed up freight trains, and in this capacity the engines thrived as designed.

Interestingly, in an effort to meet wartime demands, the railroad acquired even more that had originally been ordered by Union Pacific but diverted to the Colorado road by the War Production Board.   While the D&RGW was never pleased with these final examples - and ultimately were only leased by the railroad - the earlier examples remained in service until the early 1950s.

One of the Denver & Rio Grande Western's big 4-6-6-4's, #3713 (Class L-105), is seen here in Salt Lake City, Utah circa 1950. Stephen Bogen photo.

Prior to the 1920s the Rio Grande operated few large wheel arrangements.  According to the book, "Rio Grande Railroad" by James Griffin, its foray into big steam began with a small fleet of eight 2-6-6-2s built by D&RG shop forces between 1909-1910 (numbered 3300-3307) for service between Minturn and Helper along Tennessee Pass.  They remain in service until after World War II.

The railroad's much larger 2-8-8-2s first arrived in 1913 from Alco.  The Rio Grande was so pleased with these big steamers in standard road service - within central and western Colorado, as well as along Utah's rugged Soldier Summit - that it continued acquiring new examples through 1941 when its own shop forces produced sixteen new engines that year (3400-3415)

The Challengers

Rio Grande's big 4-6-6-4s were acquired primarily to handle fast freight assignments; utilizing big 70 inch drivers they were primarily used along the flatter territory bedtween Grand Junction and Salt Lake City as well as from Grand Junction to Minturn.

Data Sheet

Rio Grande 4-6-6-4 #3710 (L-105) departs Denver for Pueblo, Colorado during 1952. Robert Le Massena photo.

Final Years

The Rio Grande was a big proponent of the newfangled diesel, testing the FT in 1939 and purchasing its first examples in 1942.  The railroad was quick to retire its main line steam fleet and the 4-6-6-4s were no exception.  

The leased L-97's were sold to the Clinchfield Railroad in 1947, which promptly scrapped the group six years later in 1953.  Finally, the remaining L-105's were scrapped between 1951-1956.  Sadly, none were preserved.