A wagon train in a box canyon vs. Indians... (1950)

So my grandfather saw a western in a drive-in in 1950 in which a wagon train is trapped in a box canyon by Indians. As night falls, the wagoneers set lights at the canyon entrance and set guards with lanterns. One by one, though, the lanterns go out and then blackness and a scream!

That moment is burned in his mind and he would love to recapture it!

Thanks for your help!