It is Joni Mitchell. She was one of the other acts, along with Jessee Colin Young & the Beach Boys. This show was at Roosevelt Raceway on the day that Ford pardoned Nixon (a Sunday if I remember correctly). They also played at Roosevelt Stadium in Jersey City on the night that Nixon announced his resignation. At least I can still remember where I was on those 2 dates. I still have the tee shirt I got at the Roosevelt Stadium concert. Not that I can fit into it.