Republic
If this film didn't have the RKO logo I would've sworn it was a Republic western. Just look at the cast, many of whom were Republic stock company members: Roy Barcroft, Gene Roth, Tom Steele, Dave Sharpe, George Chesebro, etc.
Of course, the presence of Jane Russell, George Brent and John Litel give it major studio look. For me, Russell was more fun in the Paleface movies with Bob Hope.