With the exception of one mallet, the Class M-4A, 2-10-4 locomotives were the largest and most powerful steam on the Chicago, Burlington & Quincy. Known as the "Texas" type on most railroads, the "Q" called the type "Colorado". Built by Baldwin Locomotive Works starting in 1927, the Colorados were initially designed for use hauling heavy, slow freight trains. They were converted in the Q's own shops starting in 1934 to high-speed, manifest freight locomotives and gave excellent service to the end. All 18 locomotives in the class were retired in 1960 and sold for scrap. Two locomotives were used as stationary boilers for a time.