California Jam?
Nope. I will wait for other guesses and ping you when I own up to the event.
DallasBiff has it right. The Ozark Music Festival, a three day event in Sedalia, Missouri that may have been larger than Woodstock. (I think so.). It was a hotter than Hades weekend in July of ‘74. I talked to a guy that was hauling in block ice from Jefferson City and selling it for $10 a block which was about a 500% mark-up in 1974.
It is the only public event I have ever been to where Window Pane Acid was being sold by a street vendor hawking his goods at the top of his lungs. Besides lots of young women with sunburned breasts, my wife remarked about the “weenie-roast”. One birth and one death and a lot of overflowing toilets. The small city of Sedalia ran out of everything, including water pressure for the toilets at the State Fairgrounds.