A Concert I Went To

I thought the internet was a respository of all information, but I can't find any remembrance or mention of a concert I went to in (I think it was) 1971. In Des Moines. It might have been 1972.

Featured at this concert, at the Iowa State Fairgrounds were Leon Russell, Albert King, and J.J. Cale. Does anyone out there remember this concert or tour?

I remember J.J. Cale had a really weird looking guitar, like it was a technological marvel, holes, wires, gadgets. I got one or two Albert King LPs after that at some point. And we loved Leon at the time. Haven't heard much about him lately.