Check out this Avalon Ballroom All Texas poster! It features Janis Joplin w/Big Brother and the Holding Company, the Sir Douglas Quintet and a "Surprise Visit on Sunday" by the 13th Floor Elevators.
As with so many bands from the sixties, the Thirteenth Floor Elevators headed for California in the summer of 1966 and stayed there in San Francisco for the remainder of '66. They performed at the Avalon ballroom four times and once at the Fillmore Auditorium.
Their first album was released during their time in California and this, plus the fact they performed a lot at the Avalon ballroom, led many to think of them as a San Franciscan band. The Elevator's time in California helped to forge important links between America's West Coast and the hitherto relatively isolated Texas psychedelic scene.
Here's a quote from the 10/17/66 Mojo Navigator about the 'Elevators' performance at this gig:
"... The most interesting group musically was the 13th Floor Elevators. They are a really freaky group. They look strange, they sound strange, and they are all good musicians, doing all original material. The lead singer, whose voice is truly odd, also plays lead guitar pretty well. The drummer is excellent. They have one guy who does nothing but boop-boop-boop with a jug. The songs they do are new and different, though they tend to have a sameness because of the unchanging quality of the jug sound and the singer's voice. They will have a new single out soon and an album."