While the ballrooms ran their weekends, the Matrix — Marty Balin's small club on Fillmore Street, a converted pizza parlour with a capacity in the low hundreds — was most of the way through a week-long stand by the Blues Project.

The Blues Project were the New York band that mattered most to musicians and least to the charts: Danny Kalb, Al Kooper, Steve Katz, Roy Blumenfeld and Andy Kulberg, playing electric blues with a jazz player's appetite for the long form. Kooper and Katz would leave within the year to found Blood, Sweat & Tears; Kulberg would go on to Sea Train, who turn up later in this same calendar week on a 1969 Fillmore West bill. Sharing the week was Robbie Basho, the solo steel-string guitarist working in the raga-influenced American Primitive style he and John Fahey were separately inventing.

An out-of-town electric blues band and a solo acoustic mystic, six nights running, in a room the size of a large living room. The Matrix printed no posters, which is why weeks like this one leave almost no trace beyond the listings.