South of Hell Mountain (1971)

Their greed exploded point blank… shattering their lust into murder.

After planning to only rob a gold mine, an outlaw and his two sons end up killing all of the miners. While fleeing to Canada, they stop at a small cabin in the woods where they find a woman and her stepdaughter living together. What happens afterward is told through the memories of the step-daughter, now a patient locked away in a mental hospital.