On September 6, 1968 — a Friday — the Avalon Ballroom opened a three-night run behind FD-136, Roger Weil's poster, with the James Cotton Blues Band headlining over the Sir Douglas Quintet + 2, Pulse, and Womb (chickenonaunicycle; worthpoint FD-136 listings). By late 1968 the Family Dog's Avalon was past its 1966–67 peak — Chet Helms's operation was under real financial strain, and the room would close within months — so a deep, blues-forward bill like this one is the Avalon in its last full season, still booking well.

James Cotton, out of the Muddy Waters band, was exactly the kind of Chicago blues headliner the ballrooms had leaned on from the start; the Sir Douglas Quintet — Doug Sahm's Tex-Mex outfit, here billed "+ 2" — had relocated to the Bay Area and were regulars.

The bigger story of this weekend, though, wasn't at the Avalon and wasn't in 1968. A year later, on September 6, 1969, the Grateful Dead and Jefferson Airplane played the Family Dog on the Great Highway — and that show is worth its own careful paragraph, because almost nothing about it was advertised. It survives mainly on tape: an Owsley Stanley recording catches Jerry Garcia telling the room "Jefferson Airplane, coming up next" (dead.net; setlist.fm). Corry Arnold, who documents it, says flatly that he knows of no eyewitness accounts or reviews — only the tape. The show appears to have been unadvertised, likely because of Bill Graham contract restrictions on nearby dates; a theory that it was a make-good for the Dead's cancelled August 1 Family Dog booking (skipped in solidarity with the Light Artists Guild strike) is one commenter's plausible guess, not established fact. I'm recording September 6, 1969 as real but essentially secret; a claimed second night on September 7 I can't confirm at all, and I'm leaving it out rather than assert it.