The red car that gets cut in half by a train is one of the "Leslie Specials" from The Great Race (1965).
The steam locomotive trains used in this picture were from the Cumbres & Toltec scenic railroad that runs 65 miles between Chama, New Mexico and Antonito, Colorado. As of 2022 this tourist attraction is still in full operation. It can also be seen in Bite the Bullet (1975), Indiana Jones and the Last Crusade (1989), and Wyatt Earp (1994), among other films and television programs.
When Mayor Wilkens says McKay must be a hundred years old, Flagg protests, "He's the same age as me!" In fact, George Kennedy was eight years younger than Robert Mitchum. But he didn't say, "He's the same age as me." He said, "He's no older than I am."
The movie was filmed on location in Chama, New Mexico, and other locations in New Mexico, Thousand Oaks, California, Silverton, Colorado, and the Warner Bros. Burbank Studios, California.
Burt Kennedy: ["Fight!"] At the beginning of the fight scene, someone (in this case, an uncredited Richard Farnsworth) looks directly at the camera and yells, "Fight!"