I think it is Mackenna's Gold, only it's not a B movie. Definitely A, with Gregory Peck, Omar Shariff, and Camilla Sparv:

http://www.tcm.com/tcmdb/title/4692/Mackenna-s-Gold/

I’m trying to identify a “B” western I saw sometime at a matinee in the mid to late 1950s when I just a lad. I have no idea about the title or stars. The movies was about a group of men and one woman who ascended rocky hills and mountains with horses and pack animals to a cabin where they waited for the one day a year when the the sun rose and shone through an aperture in a rock formation, revealing a mine or treasure site. (Inspiration for a scene in +Raiders of the Lost Ark+?) I think there may have been the usual jealousy and infighting about the woman, but I’m not sure. What I do remember is that at one point the woman had a bath in a big wooden cask and an elevated or overhead shot gave a fetching display of her buoyant charms.