I was there. I recall this concert very well for various reasons. For one I remember how tired I was by the time The Doors came on stage; it must have been well after midnight. Me: I was wearing a suede leather jacket with fringe on the sleeves and bell-bottom jeans. Any how many people in the audience were just totally stoned out of their minds, most on marijuana but probably a good mixture of other things as well. And Morrison himself seemed drunk from the beginning; I think he came out with a bottle of beer in his hand.
But my most positive impressions were of the two lead-in acts, Blues Image and John Sebastian. Blues Image was just emerging as a major group (although very short-lived) but they were really polished: great instrumentation and harmony. Then after a long pause, John Sebastian came out, sat on the edge of the stage –just him and his guitar– and offered a series of lovely solo songs. I was impressed how he mesmerized thousands of doped-up hippies who had been dancing in the aisles a short time earlier and were waiting for the insanity of The Doors. His performance and the guitar work of Dickey Betts of the Allman Brothers a few years later at the University of Iowa were the best live rock events I’ve seen.