Movie about a family on a trip, and finding cannabis growing. 1970s?

My Mother saw this movie when she was younger, it was about a family going on a camping trip/vacation in the woods.. i believe.. She thinks it could have been a beach. They stumble upon weed growing, and the growers are not very happy. I think the growers kill them, or at least torture them, something along those lines. Its a thriller type movie. Possibly in the 1970s, could been 1980s. But more then likely in the 1970s. She has been trying to find the name of it for yeaaaarss! Thanks 😛 Also it is not, Terror on the Beach.. Very close, but terror on the beach does not have the weed growing in its plot.