The D&RGW had six narrow gauge air dump cars: OR, OS and 0140-0143. Ditchers OW, OX, and RGS 030 were self propelled and could pull one or two of these dump cars for short distances. A D&RGW engineer who worked on all of them, told me that they used the dump cars to put rip rap along rivers and streams. I have a report of engine 268 working with one of the ditchers and a dump car on the Ouray branch in the 20s. They were also used with flats as Jimmy describes and sometimes 700 and 800 series drop bottom gons when doing ballast work.