Roosevelt Raceway
The first concert my folks let me attend (along with two friends) without "parental supervision." This was a huge, heavily anticipated "summer's end" show that went on from the morning through way into the night. CSNY's final American appearance on their big 1974 tour, they were on stage for over 5 hours and played 32 songs. Joni Mitchell joined them after playing during the day.
We dared walk up near the very front during the Beach Boys set that afternoon, and some drunk dudes yelled and threw beer cans in our direction. So we deemed it best to watch the rest of the sets from further back on the left side.
Wikipedia has this statement under its "Roosevelt Raceway" page: "The property was utilized by several organizations for other events. The most notable event was a rock concert; "Summersault '74", which drew a crowd of 75,000 (and featured performances by Crosby, Stills, Nash & Young, Joni Mitchell, Jesse Colin Young, and the Beach Boys)."