Wasn't the published reason for tearing up the rail on Donner was that S.P. at that time was real short of cash and Texas was rail starved due to increased traffic levels? Bottle necks developed there so they justified moving the rail from Donner, which didn't have a heavy traffic demand, to Houston and other places along the Sunset Route. This gave them badly needed yard space as the trains were backing up on the main line. Also the main line rail was getting risky due to extensive wear. It's been some time and I'm a little foggy on this. Maybe some of the rails who worked the Texas area at the time can focus the picture better than this.
:)