Ken Lively's gas station and store was/is on the road north of the trestle right next to the road. It is about 50 yards northwest of the carman's house so that would rule out those buildings.
I will ask Dave Ferro about his thoughts as he and his wife Laura led teams up on Cumbres discovering and marking with those concrete piers locations of the turntable, water tank, depot, spring house and other structures.
My own guess is that it was support buildings for the families that lived up there, (like the outbuildings for the carman's house). Carlos Llamos's mother lived there as a girl with her family so perhaps she would know if shown a photo.