A mile from the Fillmore on Friday, August 19, 1966, Chet Helms's Family Dog hung what would become one of the most beloved posters in the entire canon: FD-22, the "Frankenstein" poster, Stanley Mouse and Alton Kelley's monster looming over a bill of the Grateful Dead and the Sopwith Camel, with Bill Ham's liquid lights (per wolfgangs). Its fame rests partly on a mistake: the poster misspells the headliner "Greatful Dead" — a limited-run error, uncorrected because the artists had not yet fixed the spelling in their own minds, that turned, as Wolfgang's puts it, "into gold for collectors." On the same August Friday, then, the two rooms produced a piece of pure imported pop craft (the Young Rascals at the Fillmore, BG-24) and a piece of accidental folk-art immortality — the Fillmore and the Avalon, rivals and twins, each doing exactly what it did best.