Mystery Mountain is a 12 part Mascot Pictures serial where silent movie cowboy Ken Maynard is trying to track down a nefarious criminal called the 'Rattler'. This dude who when he's not walking around posing as other cast members with life like masks is busy trying to get a feud going between a railroad and a freight wagon outfit that's owned by leading lady Verna Hillie.
The railroad is busy digging a tunnel into a mountain where the 'Rattler' has a vested interest. But sent to get to the bottom of all this is range detective Ken Maynard together with a sidekick, newspaperman Syd Saylor, looking for a scoop as all good newspapermen do.
Maynard's horse Tarzan has absolutely nothing on Trigger, in fact I think Tarzan ought to ask for a recount or demand to know when the election was held that named Trigger the smartest horse in the movies. He pulls Maynard's gluteus maximus out of the proverbial sling a few times in Mystery Mountain.
In fact Tarzan's the one who finally after 12 chapters identifies who the 'Rattler' really is beneath those disguises as other cast members and going around in a Phantom of the Opera like disguise for most of the film. I won't give it away, but the hint for the viewer who wants to sit through the four hours of this serial is: think The List of Adrian Messenger and how they nailed Kirk Douglas in that one.
By the way do you it's possible that John Huston and the writers who worked on The List of Adrian Messenger got inspired by Mystery Mountain?
If you look at the cast list of Mystery Mountain you will note the names of Gene Autry and Smiley Burnette. Both in fact were brought to Hollywood by Ken Maynard who met them in Chicago when he was doing a personal appearance tour and they were doing radio. This was the second of two serials they did literally learning the picture business, courtesy of Ken Maynard.
According to a recent biography of Autry, Public Cowboy Number 1, when Hollywood had totally abandoned Ken Maynard and he was living in poverty in a trailer park, Gene Autry sent him regular checks until the day Maynard died to keep him literally in eating money. Maynard was not the nicest guy in the world, but at least one man was grateful for a kindness shown.
I will say this for Mystery Mountain, at least it did not attempt to rewrite history as some serials I've seen did. It's a Mascot film so don't expect too much/