Anderphoto:
What's even more unusual is seeing UP 4-8-8-4 #3985 on a freight or a double stack! I know of at least two instances of that happening, so there were probably others.
The Union Pacific #3985 is a 4-6-6-4 Challenger type, not a 4-8-8-4 Big Boy Type. I don't recall what year it was, but some years ago American Presidents Line (APL) specifically requested that Union Pacific assign one of their Steam Locomotives to a stack train, for publicity purposes. The #3985 got the assignment. If a present era modeler had an itch to run a Challenger, they could run a solid stack train of APL containers, and have a prototypical (even if only a one time occurance) train.
UP has also used both the 844 and 3985 in freight service to break them in after major service. I have also read that UP will occasionally use either Steam locomotive in revenue freight service just to for the surprize factor, without announcing that they will be out on the loose. It is not very often, but they can show up in unexpected places, at unexpected times.
I am Very Happy, that UP decided to keep any Steam at all in operable condition, and donate many to Cities and Museums for display, rather than follow the New York Central's example, where very few Steam Locomotives escaped the scrapper's torch(boderline crime against society, not even 1 of those Famous Hudson's survived). I have no doubt that the UP Steam Program is an Immense expense, so BIG THANK YOU to UNION PACIFIC, from Me.
Doug