The Trips Festival was held at the Longshoreman's Hall in San Francisco over three days in January of 1966. The festival was the brainchild of Stewart Brand, a Prankster and later publisher of the Whole Earth Catalog. Brand and Ramon Sender did most of the early organizing. The festival roughly followed the format of the earlier Acid Tests and, by all accounts, it was equally chaotic and off the wall (despite the best efforts of Bill Graham and his clipboard).
The Pranksters were involved early on, and on Saturday night they provided their usual homemade inter-active technology and wacked-out craziness. The Dead played -- well, sort of -- as did Big Brother and the Holding Company, along with lots of other musicians and artists. Kesey offered the crowds a running commentary of the craziness on an overhead projector. The audience were encouraged to be more than just spectators and many wore "Ecstatic Dress" and danced the night away as the fliers had requested. A bag of LSD circulated around the hall courtesy of Owsley himself.
Ben Van Meter - S.F. Trips Festival, An Opening (1966):