Original 1st printing 13&3/4 x 19&5/8" concert poster for Country Joe & the Fish appearing at the Jabberwock on "Sunday" (no date appears, but there is a reference to the "October Fish Calendar", which was issued in 1966).  

Art by Jon Adams, a nearly-identical image is featured in the Art of Rock book on page 217 (plate 2.281). This version swaps out the red background for blue and features a group of (plugged-in) fish replacing Country Joe holding a fishing pole in the basket of the balloon.

 Thin flat vellum stock poster is in near mint to excellent (A-/B+ to B+) condition; aside from a hairline-thin 2" diagonal bend along the lower left margin, a VERY light amount of creasing/handling wear and a couple of soft corner-tip bends, it is a FANTASTIC-looking example of this whimsical late-'66 Country Joe & the Fish poster from Berkeley.