Supernatural/Horror Film with Indians

[Gothic]

I remember seeing a film in the late 70's or early 80's. A group of men (possibly cowboys) come across a woman tied to a tree, she claims to have been captured by a tribe of indians. After they release her, they are killed off one by one by the 'indians' although you never see them, the only evidence found is arrows. Finally the last survivor realises it is the woman who has been killing them, before he to is killed. The film ends with a shot of the woman again tied to a tree about to be rescued again.

I have searched for this film without luck for many years, can anyone help with this?