Two shows across town on the same Thursday, July 28, 1966, and that collision is the whole story here.

The hero of the day is the Avalon Ballroom, where the Family Dog opened a three-night run — July 28 through 30, 1966 — with Bo Diddley headlining over Quicksilver Messenger Service. The poster is FD-18, drawn by Stanley Mouse and Alton Kelley, and it's the one collectors nickname "Voice of Music" because it lifts the RCA Victor "His Master's Voice" trademark — the dog Nipper cocking his head at a Victrola — and repurposes it, unauthorized, for a psychedelic dancehall bill (classicposters, poster/18, listed "7/28-30/66"; concertpostergallery lot 1606 credits Mouse/Kelley; rockposters.com). There's a Type-B handbill variant for the same show carrying the Bo Diddley / QMS bill (abebooks). Worth pausing on that pairing: Bo Diddley was one of the founding fathers of rock and roll, and here he is topping a bill in a converted San Francisco ballroom over Quicksilver, a band that hadn't yet cut a record — the old guard and the new scene sharing a stage.

But the reason July 28, 1966 is worth marking twice is what was happening across town the same night. At California Hall, the counterculture threw a Tolkien-themed party billed as "Bilbo's Birthday" — a Hobbit celebration — with Big Brother and the Holding Company (Janis Joplin), the Great Society (Grace Slick), and The Charlatans on the bill, lights by Elias Romero and Ray Anderson. The flyer is catalogued as AOR-2.156 (rockposters.com, California Hall, 7/28/1966; concertposterauction shows two "Bilbo's Birthday" variants).

The sweetness of that lineup is hard to overstate in hindsight: Janis Joplin and Grace Slick — the two voices that would come to define the San Francisco sound — on the same Tolkien-themed bill, on the same night Bo Diddley headlined the Avalon. In the summer of 1966 none of that was obvious yet; it only reads as a summit from here.

There may be a mechanism behind the collision, though I want to hold it loosely. The San Francisco Sound family-tree show lists (thesanfranciscosound.blogspot.com) record the "Bilbo's Birthday" bill as originally set for July 22 and moved to July 28 — which, if right, is exactly why two major bills ended up stacked on the same Thursday. But that postponement doesn't show up in the poster and dealer listings for AOR-2.156, and a July 22 California Hall date also circulates as if it were its own separate event, so I won't state the move as settled fact. Either the show slid six days and landed atop the Avalon's opening night, or two California Hall dates are being conflated in the record; the family-tree lists favor the former, and I'll leave it there.

One honesty note on the California Hall piece: the poster's artist is genuinely uncertain, and the sources don't agree. Classicposters.com attributes AOR-2.156 to "Passalaqua"; one flyer variant is instead credited to "C. Harris," and another carries no credit at all. Three different answers — a dealer attribution, a variant credit, and an uncredited printing — so I won't assign it the way FD-18 cleanly belongs to Mouse and Kelley. Treat the attribution as unsettled, with Passalaqua the leading candidate per the catalog dealer.

The date kept turning up bills in the years after, if with less symmetry. On July 28, 1967 (a Friday), the Avalon ran the second night of an FD-73 stand — Blue Cheer, Captain Beefheart, and the Youngbloods, poster by Tom Glass. That was also the night the Fillmore's BG-75 run famously changed hands: the bill had been the Yardbirds, and it flipped to the Doors, who opened July 28 over James Cotton and Richie Havens. A year later, July 28, 1968 (a Sunday), brought Quicksilver Messenger Service back to the Avalon over Howlin' Wolf and Dan Hicks and His Hot Licks, poster FD-130.

Then the date goes quiet. July 28, 1969 (a Monday) is an honest null: both principal venues were dark. The Fillmore West and the Family Dog on the Great Highway had each run July 25–27 and closed out before the 28th, and the Avalon had shut its doors back in November 1968. Nothing to report, so I'll report nothing. And 1965 is simply pre-scene — before any of this existed.

So the anchor stands on 1966: two real posters, two real shows, one Thursday — and the only reason we get to tell them side by side is a show that slipped six days off its calendar and landed on the wrong, or the perfect, night.