Georgetown Loop Railroad No. 21 is a 44-tonner center-cab type narrow gauge diesel locomotive built by General Electric (GE) in May 1957, originally for the Colorado Fuel & Iron Railroad Company. It was later sold to the Rocky Mountain Steel Mills Railroad Company where it would continue to operate in regular service until its retirement.
Following its retirement, it was eventually sold to the Georgetown Loop Railroad between Georgetown and Silver Plume, CO. It is used on the Georgetown Loop in both switching operations, as well as operating tourist excursion trains between Georgetown and Silver Plume, CO where it remains in service as of today.