Well I can help narrow it down a little. I know it ran in 1976, cause I was out there for a week volunteering. I have movies of it running in July I think. Not sure if 1976 was the last year, or if it ran into 1977, but I would bet it was one of those years. Earl may know if he was out there around that time.
Greg Scholl
[www.gregschollvideo.com]