Most of the Rio Grande locomotives were made at the Baldwin Locomotive Works and the American Locomotive Company . The numbers assigned to the locomotives has a complex history and is hard to understand without learning all the details of who owned the railroad, what railroads were failing, what year it is and on and on. However, one can simplify the whole thing by thinking of the eqipment in two time frames, before and after 1924. It was in 1924 that a major renumbering of all the railroad equipment was made and it is easiest to think of the numbering system as before and after. Keep in mind that the roster changes for each year.
New equipment is purchased.
Old warriors are scraped. Most of the railroads steam locomotives had been purchased by 1939 so this year gives a good cross-section in time to examine the equipment the railroad owned in the second half century of operation.