Thanks for a wonderful presentation. The drone view gives the impression that the land is mostly flat, but the route is extremely serpentine. What was the purpose of the train? Eighteen cars is significant number for just a customer or employee special.
Looks like ex-SP track in the area around the San Luis Obispo CA, from about Tunnel 11 near Chorro to the vicinity of Cal Polytech. From 2:00 to 2:10 you can see evidence of the roadbed for a wye where a track to Camp San Luis Obispo once connected.
Exactly the spot, researching it for Coast Starlight layout. Also been through a few times on the Coast Starlight, it's a beautiful section from onboard the train.