Galloping Goose is the name given to a series of seven railcars (also known as "motors") built in the 1930s by the Rio Grande Southern Railroad (RGS) and operated until the end of service on the line in the early 1950s.

Originally running steam locomotives on narrow gauge railways, the perpetually-struggling RGS developed the first of the "geese" as a way to stave off bankruptcy and keep its contract to run mail to towns in the Rocky Mountains in Colorado. There was not enough passenger or cargo income to justify continuing the expensive steam train service at then-current levels, but it was believed that a downsized railway would return to profitability. The steam trains would transport heavy cargo and peak passenger loads but motors would handle the lighter loads

(Info taken from Wikopedia)