I double checked, and as I suspected this movie was one of the ones shot on the Spahn Ranch during the lead up to the Manson murders.

And yes, there are most likely Manson Family people in the cast.

Holy shit, I had to go check imdb to see if my uncle was in this.

Doesn't look like it.

Your uncle was in the Manson family?

Yup.

According to him, when they rode the black bus they were all knocked out with drugs, then they woke up to be told that the black bus had flown to the top of a mountain without using the roads. He believed it.

In retrospect, that's a very North Korean holy leader magic sounding story, or something out of Old Hassan's mountain.

Wow!