According to rockprosopography101.blogspot.com “due to riots in the Fillmore district, the October 1 (Friday) show was rescheduled from Winterland to the Fillmore, but was still only attended by a few hundred people.”
13th Floor Elevator did not play due to a contractual issue with Family Dog, who had them to play their San Francisco debut the following weekend at The Avalon Ballroom.
Quicksilver Messenger Service replaced them on 26th, while Country Joe And The Fish was the replacement on the 27th, Country Joe’s first Fillmore show.