On Friday, September 27, 1968, the Avalon Ballroom opened one of the most improbable-looking bills of the whole Family Dog era: Flatt and Scruggs — the reigning royalty of American bluegrass — headlining a psychedelic ballroom over Ramblin' Jack Elliott, the Sons of Champlin, and Country Weather (per chickenonaunicycle's Family Dog list, Wolfgang's, and the dKing Gallery catalog record). The run went Friday through Sunday, September 27–29, 1968.

It is worth sitting with how strange, and how characteristic, that booking was. Lester Flatt and Earl Scruggs had spent two decades as the most famous bluegrass act in the country; Scruggs's three-finger banjo roll was, quite literally, the sound most Americans meant when they said "banjo." In 1968 they were also, unexpectedly, having a pop moment — "Foggy Mountain Breakdown" had been used in the previous year's Bonnie and Clyde, and the theme from The Beverly Hillbillies had made them household names. Chet Helms and the Family Dog putting them at the top of an Avalon bill, in front of a light show and a dancing psychedelic crowd, is a small monument to the omnivorous curiosity of the San Francisco scene at its height — the same instinct that had already brought bluegrass, Delta blues, free jazz, and Indian classical music onto ballroom stages. Ramblin' Jack Elliott, the singing cowboy and Woody Guthrie disciple who had been a direct conduit of the folk tradition to Bob Dylan, sat second — another root of the music, planted right there on the bill. Under them came two homegrown Bay Area bands: Marin County's Sons of Champlin, with their horn-driven, jazz-tinged sound, and Country Weather, one of the era's hard-working second-tier local groups.

The poster, FD-139 in the Family Dog series, is a Wes Wilson design — and by 1968 that name on a Family Dog poster was itself a kind of statement, since Wilson had largely broken with Bill Graham two years earlier over money and credit. The image, built around a photograph of an abandoned California gas station (the photo credited to Jim Smircich), has long carried the collector nickname "Holy City Service" (Wolfgang's, dKing Gallery, and rockposters all attribute the piece to Wilson; chickenonaunicycle's list names Wilson and the full bill). It is a quieter, more photographic piece than the incandescent lettering Wilson had made his name on in 1966 — a sign of how far the poster idiom had traveled in two years.

The same Friday night, across town, Graham was running his own landmark event at the Fillmore West — the middle night of the Mike Bloomfield / Al Kooper "Super Session" stand on Lee Conklin's BG-138 poster, the run that produced the Live Adventures double album. A reasonable case could be made for either as the day's hero; the Avalon FD-139 gets the nod here because it opens on the 27th and because the sheer incongruity of Flatt and Scruggs beneath a Wes Wilson poster is the more surprising, more purely San Franciscan story. The Bloomfield-Kooper run is carried as the day's strong co-event rather than buried.

Across the rest of the timeline, September 27 thins out fast. In 1969 the date was the third night of Chuck Berry's Fillmore West run (BG-193) and also saw the non-BG Flamin' Groovies rental at the old Fillmore and a Family Dog on the Great Highway bill (Floating Bridge and others), none of which carry a confirmed poster beyond the Berry piece. In 1966 the Fillmore hosted a Four Tops Motown booking — a real Bill Graham show, but off the psychedelic-ballroom genre and without a confirmed series poster. In 1967 the Straight Theater ran a mixed-media benefit for the Haight-Ashbury Free Medical Clinic, and 1965 offers only a Matrix "hoot" night. The load-bearing claims here — the bill, the FD-139 catalog number, the Wilson attribution, the September 27–29 dates — are corroborated across multiple independent archives; what stays hedged, as ever, is the exact per-night makeup of a three-day run.