Hey, thanks for all the retro-trauma, and thanks for linking my blog in your sidebar.
I've just spent some time looking back at every "Name That Trauma" post from your most excellent site, and was unable to find any reference to my film in question. I saw it at the theater in 1975 or 1976 as a five or six-year-old, and I'm assuming it was first-run. It was a matinee, but not a kiddie film, as I recall some PG-level sexual content. The most traumatizing bit was a woman with white hair and white skin who was out in the woods and threatening some people in a cabin. She had no lines, but just snarled at the camera. More specifically, there was a Native American Shaman-guy who had some magical powers. At one point, he dumps some powder out of a small leather bag on his belt to create a line across a road. A car drives up and smashes into it, as if it were an invisible wall. That's about all I remember.
I'm sure this movie actually happened. I'd love to see it again to check if that white-skinned woman is as horrifying as I remember, or just laughable in retrospect. Won't someone help?