In the realm of there's-a-prototype-for-[nearly]-anything:
The Royal Gorge had just had piggyback refers coupled onto the rear end. I'll try to research when Dad took the pic, probably 1964.
ON EDIT: According to utahrails.net:
"1964
Up to four 85ft TOFC flats were added to the end of the Prospector carrying Rio Grande Motorways and grocery chain trailers between Denver-Grand Junction and briefly to Salt Lake."
The Prospector and the Royal Gorge ran as one train from SLC to Grand Junction (and reverse) so Dad took this pic at Grand Junction. Summer '64 we did indeed ride the Royal Gorge from Denver to SLC.