While the Avalon and Winterland drew the big crowds on October 7th, something quieter was happening in a hundred-seat beer-and-pizza joint at 3138 Fillmore Street in the Cow Hollow neighborhood.

The Matrix was Marty Balin's club — the Jefferson Airplane singer had founded it in August 1965 as a home base for his new band, persuading three partners to put up $3,000 each. It was tiny, intimate, and became legendary precisely because of its size. At the Matrix, you didn't watch a band from across a cavernous ballroom. You were in the room with them. You could hear them breathe between songs.

By October 1966, the Matrix had become the place where San Francisco's famous bands worked out new material before taking it to the big stages at the Fillmore and the Avalon. A handbill advertised a run of roughly ten nights — October 7 through 16 — for the Texas bluesman Lightnin' Hopkins, though Ralph J. Gleason later suggested Hopkins didn't actually open until October 13, and chickenonaunicycle flags the October 7–8 billing as possibly a carry-over from the previous week's ad. Either way, a Matrix booking meant room to stretch, experiment, fail, and try again — all in front of an audience of maybe sixty people who'd paid a dollar to get in.

The club's influence went far beyond its capacity. It was at the Matrix that music critic Ralph J. Gleason first saw the Jefferson Airplane and became their champion. It was at the Matrix that many of the relationships that defined the San Francisco scene were forged in the close quarters of a room where the stage was barely separated from the audience.