The summary on IMDB calls "Mountain Rhythm" 'standard western fare', and I have to agree. In B-westerns, most films fall into about three plots...and they repeat these themes again and again. The most familiar of these is the baddie who wants to throw all the ranchers or miners off their land. In many cases, it's because the person is greedy and wants all the grazing land to themselves. In "Mountain Rhythm" it's an odd motivation....as the baddie wants to force everyone off the land so that they can build a gigantic luxury resort!! It's odd, as when the story begins, they already have a giant luxury resort! but, I guess being baddies, they just want it bigger and all to themselves. So, they use all sorts of underhanded tactics to try to get the ranchers to go. And, when that doesn't work, they resort to stealing the money the ranchers have collected in order to buy the range! So, it's up to Frog and Gene (Smiley Burnette and Gene Autry) to get the evidence and bring goodness to the not so old west. I say 'not so old' because like many of Autry's films, it's set in modern times...with buses and telephones and the like....as well as horses and cowboys.
Even though this is a very standard plot, it is handled pretty well. Maude Eburne is wonderful as Aunt Matilda (Ma Hutchins) and I did love the song "Hobo's Dream"...it was very catchy. But otherwise, it was all very typical of most Bs of the era....not bad at all but also a certain sameness to all this.