I just found this just now by accident 9and was at this concert)
My roommate Eric (who introduced me to Zappa and PKD) and I bought my much older sister and her bf/husband to be tickets for the ride.
We were 15 and sophomores in high school.
We provided her bf acid too to her butt hurt.
The opening acts were The Collectors and Its a Beautiful Day. Traffic was supposed to be 2nd billed and the show was advertised and tickets sold for that lineup but Traffic cancelled and was replaced by Its a Beautiful Day.
Not that long before Eric and I and Chuck went in Chuck's mother's Volvo and Chuck's new driver's license to San Francisco from Danville in the East SF Bay Area. We went to the Haight and to the then new Tower Records at Columbus and Bay near Fisherman's Wharf. I bought Cream's Disraeli Gears and The Stone's Satanic Majesties Request. I bought an Indian bedspread at Cost Plus.