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.