Here's a 1946 Hootenanny reference attributed to Woody Guthrie.

"We was playin' for the Lumber Workers' Union. We was singin' around in the shingle mills. There was a lady out West out there in the lumber camp and her name was Annie and so every time they'd have a songfest Annie would outshout all of them. So people got to call her Hootin' Annie but the name got spread all over and so out there when they are going to have a shindig they call it Hootenanny."

And that's how Hootenannies began, according to Woodrow Wilson ("Woody") Guthrie.