On Friday, September 30, 1966, the Avalon Ballroom opened a weekend built around a genuine Texas import: the 13th Floor Elevators, the Austin band that had put the word "psychedelic" on a record sleeve before almost anyone in San Francisco, headlining over Quicksilver Messenger Service, one of the Avalon's own house bands (per chickenonaunicycle's Family Dog list, Wolfgang's, and Heritage Auctions, which all give the September 30 – October 1 dates and the bill). It was a Friday-and-Saturday stand.

The Elevators were a strange and important presence in San Francisco that fall. Roky Erickson's band had already released "You're Gonna Miss Me" and their debut album, The Psychedelic Sounds of the 13th Floor Elevators — a record whose title alone stakes a claim, and whose electric-jug drone and acid-evangelist liner notes made them one of the earliest bands anywhere to organize an entire identity around the psychedelic experience. They had relocated to California for a stretch in 1966, playing the Avalon and the Fillmore and trading influence with the local scene before Texas legal troubles pulled them back home. Sharing the top of the bill with Quicksilver — Gary Duncan and John Cipollina's band, as San Franciscan as any group in the room — made for a neat two-way current between the Austin and the Bay Area strains of the new music.

The poster, FD-28, is one of the most recognizable in the entire Family Dog series: the Stanley Mouse and Alton Kelley design collectors have long nicknamed the "Zebra Man," built from a striking found image the pair recolored into the Avalon's palette. Mouse and Kelley, working out of their studio partnership, were at this point defining the visual language of the Avalon in the same way Wes Wilson was defining Bill Graham's Fillmore; FD-28 sits early in that run and remains a signature piece (Wolfgang's, rockposters, and Heritage all attribute it to Mouse and Kelley and confirm the catalog number and dates). One superlative worth hedging rather than stating flat: the record around the Elevators is thick with "firsts," but the safe framing here is simply that the band arrived at the Avalon at the peak of their brief, incandescent moment, with their debut album barely a year old.

Two other events press on this date and both are carried honestly rather than folded into the hero. Across town the same Friday, Bill Graham was running the Winterland leg of his Jefferson Airplane / Paul Butterfield / Muddy Waters weekend — the September 30 night of the multi-date BG-29 "The Sound" poster by Wes Wilson (this chronicle already carries BG-29 as a live event on its September 23 page; the poster's own printed dates include the 30th at Winterland, corroborated by the Portland Art Museum's record and the Winterland show list). And in 1967, September 30 was the second night of the Grateful Dead's Straight Theater "dance class" pair — the Saturday of the September 29–30 run widely cited as Mickey Hart's first shows with the band. That is a real and significant event, but it was billed as a dance class to work around the Straight's missing dance-hall permit, and it carries no numbered poster; it is noted here as the day's most historically weighted non-poster event rather than as the hero.

The two draft rows this chronicle already held on September 30, 1966, were checked and corrected in this pass. The first, catalogued AOR-2.121 at the Matrix, turns out to be a modest handbill for a folk singer named Andrew Staples — a real artifact, but a coffeehouse-scale booking, not the day's ballroom story; it is kept only as a footnote, with a caution not to confuse it with the adjacent AOR-2.122 (a Blues Project handbill). The second, "Whatever It Is," was a forty-eight-hour experimental happening staged at San Francisco State College from September 30 to October 2, 1966 — a campus event with a remarkable roster (the San Francisco Mime Troupe, the Committee, the Congress of Wonders, the Grateful Dead, Mimi Fariña, the Wildflower, a Bill Ham light show), documented by deadsources.blogspot and the University of Nebraska's Sixties Project archive. It is real and correctly dated, but it happened on a college campus, not in a ballroom, and whether it belongs in an SF-ballroom-poster chronicle is a scope judgment left explicitly to the human reviewer; if kept, its venue should read "San Francisco State College" and its poster recorded as an honest gap.

In 1965 there was no San Francisco ballroom event on the date — the Family Dog's first Longshoreman's Hall dance was still weeks away — and in 1968 the ballrooms were dark on the Monday. In 1969 the Family Dog on the Great Highway held the "Tom Mix Memorial Ball" headlined by Commander Cody and His Lost Planet Airmen, though the supporting bill is reported inconsistently across sources and no catalog poster could be confirmed. All of which leaves the 1966 Avalon stand as the clear center of September 30: the 13th Floor Elevators and Quicksilver, under one of Mouse and Kelley's most enduring posters.