I have this slide. Al Chione sold it a couple of lifetimes ago. I think it is a Kindig shot.
As of the 1990s' , there were still signs of the oil on the ground there.
A couple of things I've caught on looking at this with older eyes:
How did the trucks end up several car lengths away?
Notice the sand on the mainline. Something sat there for a while with the sanders running, then headed off west with them still running.
The eastbound is coming up through the siding. Then I noticed the derailed car is not clear of the main track. Maybe it is just in the clear if they came up through the siding.
Only a guess, but I'm guessing a major train handling error here. The tank was toward the head end. The long westbound had loads of pipe behind the empty tanks. The grade is flat to ever-so- slightly up grade from the bridge to the switch. The engineer should have been pulling the train to keep it stretched, but got lazy and decided to let the long heavy back portion shove him through the sag. When this car got to the switch the slack came roaring in and clobbered the head end of the train hard enough to lay this car over on its side. Perhaps the trucks ended up where they are because a crew went up there, put a chain on them, and simply dragged them west until they were in the clear.
A similiar situation happened at Coxo about the same time, only that time 499 nearly went over, and the train with several wooden cars behind the engine piled up quite spectacularly.