Union Pacific Cheyenne Yard Shop Railroad?

So, I remember watching a Union Pacific documentary on the steam era, and in it they interviewed some old engineers and fireman. One of them I remember mentioning something about a miniature railway that UP had built in Cheyenne yard to transport materials around for the shops and stuff, and that they even had a whole turntable for it. I recently remembered this random thing I had heard and tried to look into it with a friend of mine, only to turn up empty handed with a few far away photos (that are sadly PNG files) The only things we know is roughly where it was (if you look at aerial photos from the 40's there's a small turntable thing with tracks leading into it on the east side of the yard), and that there was a similar miniature railway in Omaha that served the shops there, confirmed by pictures. The only other things we know is that it was there in the 40's. Does anyone have any info on this railway? Even just a closer photo of it will do.