Saturday, August 13, 1966 closed a two-night Family Dog weekend at the Avalon Ballroom with Bo Diddley headlining over Big Brother and the Holding Company — Janis Joplin's band, still the Avalon's own local act, a year before Monterey made them national.

The poster is FD-21, and collectors call it "Earthquake." Mouse and Kelley built it around a photograph of the Sonoma County Court House after the 1906 quake, the building slumped and broken, printed in bright red and blue with fine blue lines separating the letters of the word itself. Only about a thousand originals were run, on vellum, carrying no credits but the artists' — which is why a clean first print is hard to find and why the later printings, on uncoated index stock, are so often mistaken for it.

There is something apt about that image on that bill. Bo Diddley had been making records for eleven years by 1966; the band beneath him had yet to make one that counted. The Avalon put a picture of San Francisco falling down on a poster for a night when the city's music was being rebuilt.

Bo Diddley in August 1966 was thirty-seven years old and eleven years into a recording career, and the position he occupied on bills like this one is worth being precise about. He was not a nostalgia act. He was a working musician on the R&B circuit whose rhythmic vocabulary — the "shave and a haircut" clave he had built a career on, the tremolo guitar, the maracas — had been absorbed so completely by the bands beneath him that they often did not know they were quoting him. The Rolling Stones, the Animals, the Yardbirds and Quicksilver had all taken something from his records. Two weeks later he would headline the Avalon again on FD-20 and play the Fillmore on the same trip, one of the multi-venue packages the two halls ran when a touring act was worth splitting.

Big Brother and the Holding Company, second-billed, had been a band for less than a year. Janis Joplin had arrived from Texas that June — Chet Helms, who ran the Family Dog and had known her in Austin, had sent for her — and by August she was singing with them at the room Helms ran. Their first album was more than a year away and would be made badly, for a small Chicago label, before Columbia bought them out. On this night they were the Avalon's own house band opening for a Chess Records legend.

That is the arrangement worth noticing: the Family Dog booked the roots of the music under its local acts constantly and deliberately, and it is the single clearest difference between Chet Helms's programming instincts and Bill Graham's. Graham did it too — Chuck Berry, Count Basie, Bukka White all played his rooms — but Helms did it as a matter of course, and the Avalon's poster series is thick with names from the 1930s, 40s and 50s standing beneath bands with no records out.

A note on the artifact for collectors, since FD-21 is one of the sheets people get wrong. Roughly a thousand first-printing copies were run on vellum, carrying no credit line but Mouse and Kelley's own. Later printings used uncoated index stock. The two are routinely confused, and the difference is substantial in the market.