The weather system that existed there at that time extended to the east slope of the Rockies and was quite humid. The contrail should have persisted all the way to Phoenix for awe808 and certainly as far as LA for UPS902.
Interesting data, thank you. Was that at surface or at altitude?
Wonder what the altitude was for forming persistent (low sublimation rate) ice crystals... (There can be a lot of difference between 30K ft and 39K ft.)
At some point, UPS 902 would have descended below that level...