On September 9, 1966 — a Friday — the Fillmore Auditorium opened a two-night run behind BG-27, with the Mothers of Invention over Oxford Circle. The poster is signed "John H. Myers – '66" — not Wes Wilson, as it's sometimes assumed; the attribution is confirmed on the piece itself (thirdmindbooks; olsenart.com/fillmore1.html, which lists "The Mothers, Sept 9,10 John Meyers 66"). It ran September 9–10.

This is Frank Zappa's Mothers at a real hinge point: *Freak Out!*, their sprawling debut double album, had been released only weeks earlier, in the summer of 1966. So the band that walked into the Fillmore that Friday was, for most of the audience, brand new — the record was barely out — and already doing the thing that made them singular: satirical, difficult, tightly rehearsed music aimed at the very hippie audience that had come to see them. The Mothers at the Fillmore is Los Angeles's weird cousin visiting San Francisco's scene and needling it a little. Oxford Circle, a Bay Area band, opened.

Across town the Avalon opened its own weekend: FD-25, the Mouse & Kelley poster nicknamed "Indian," with Quicksilver Messenger Service and the Great Society, September 9–10 (denverartmuseum.org 2007.4367). The Great Society is worth flagging, because it's a genuine snapshot: this was Grace Slick's band, and she was still in it — her move to Jefferson Airplane didn't happen until the middle of October 1966. Within a couple of days the Great Society would play a final all-nighter and dissolve; on September 9 they were still a going concern, sharing an Avalon poster with Quicksilver.

It is worth sitting with what the Mothers of Invention actually were on a San Francisco bill in September 1966, because the usual shorthand — Zappa, satire, weirdness — flattens it. *Freak Out!* had been released that June: a double album by an unknown band, which almost nothing in 1966 was, containing doo-wop pastiche, twelve-minute percussion collages, and songs whose target was not the establishment but the counterculture's own credulity. "Who Are the Brain Police?" is not a hippie anthem. Neither is "Trouble Every Day," Zappa's flat-eyed account of the Watts riots, written while the city burned and delivered with no romance about it at all.

Zappa rehearsed the Mothers like a bandleader rather than a rock musician, drilled them hard, and pointed the result at exactly the audience most likely to assume he was on their side. Bringing that into the Fillmore in 1966 — a room whose whole premise was communal transport — was a provocation, and a funny one. Oxford Circle, the Davis-by-way-of-Sacramento band who opened, were a straightforwardly excellent psychedelic group who would break up within the year, their guitarist Gary Yoder going on to Blue Cheer's later lineup.

The poster is a genuine cataloguing oddity and this chronicle should say so plainly: BG-27 is signed "John H. Myers – '66" on the piece itself, and it is regularly assumed to be Wes Wilson's because almost everything in that range is. It is not. Myers is a name that appears in the Bill Graham series and then essentially vanishes from it — one of the designers the numbered series absorbed without making famous, in the same category as Roger Weil at the Family Dog. The series is remembered through five or six names; it was made by considerably more than that.