The picture was taken in August of 1989.
The Animas River Railway was part of the D&SNGRR.
Perhaps others can fill in details or correct errors, but as I remember it the motorcar and trailer provided local service between Rockwood and Cascade. It was called the ARR so that the D&S could still claim to be 100 percent steam powered. Don't know now long the service lasted, or what variations in route and schedule there might have been, but as I recall the service died becasue of the unreliability of the motorcar...breakdowns were frequent.
The White Pass & Yukon has a similar motorcar, which I believe was intended to provide service between Lake Bennett and Carcross. I have a picture of it somewhere, will scan and post if I can find it. It would be interesting to see how similar the two cars look.