Greg,
Those are all good, scenic locations. If I understand correctly (I'm just a voluntary advisor to the director and location manager) the tank itself is secondary to the scenes they're trying to match to the story. In this case, the high desert scenery makes Lava Tank a better choice than the others you mentioned. There are other scenes that will be filmed and I've suggested those places to the crew.
It's been a blast to share my favorite railroad the film crew. I'm hoping they schedule a scouting trip to the C&TS soon (I'm not waiting, I'm going to be there on opening day for personal reasons).
Thanks for the information everyone!
Greg Coit
Eureka, CA