I saw this on TV around 1980 but the movie was older. Cowboys moving wild horses. Along the way they meet a woman who joins them. There attacked by Indians who are using arrows with a symbol on them. Towards the end of the movie we see that the woman has a tattoo on her upper back that's the same as the symbol on the Indians arrows, she is working with them. I think it may have had the word 'Mountain' in the title. I was only around 12 at the time and it was on after midnight, it scared the heck out of me going to bed that night. I've searched books on movies and online but I've yet to find it. Any suggestions would be greatly appreciated.