On the same June weekend that Wes Wilson's BG-11 went up across town at the Fillmore, something quieter and just as consequential happened at the Avalon: two young artists put their names on a poster together.

The show was Captain Beefheart and His Magic Band with the Oxford Circle, June 17 and 18, 1966. The poster — FD-13 in the Family Dog series, known to collectors as "the Red Bull" for the snorting bull at its center, a sly visual pun on Beefheart's name — was Stanley Mouse's first Family Dog poster. And it carries two names: Mouse and Alton Kelley.

That pairing is the reason this poster belongs in the opening week. Of the five artists usually named as the masters of the San Francisco psychedelic poster — Wilson, Mouse, Kelley, Rick Griffin, Victor Moscoso — two of them began working together here, at the Avalon, just as Chet Helms took the reins of the Family Dog. Mouse and Kelley had met the year before; Kelley had drifted into the scene from Virginia City, Nevada — the very town where the Charlatans and the Seed had started it all a year earlier. Now, in the summer of 1966, the partnership that would produce some of the most famous images in rock — the skeleton and roses, the Zig-Zag man — was getting its start in a poster about a bull.

There is a footnote worth keeping honest: the exact "first Mouse and Kelley collaboration" is hard to pin to a single poster, since several 1966 Avalon pieces carry both names. What is documented is that this was Mouse's Family Dog debut, that both men are credited on it, and that it sits right at the beginning of their work together. The legend started somewhere around here.