At which festival did The Rolling Stones play when a fan was tradically killed by Hells Angels?

Explanation

The Altamont Speedway Free Festival was a rock concert held on December 6, 1969, at the Altamont Speedway in northern California, with the Rolling Stones taking the stage as the final act. The event is best known for considerable violence, including the death of Meredith Hunter and three accidental deaths. During The Rolling Stones performance, Hunter attempted to climb on stage, and was driven off by members of the Hells Angels motorcycle club who had been contracted to serve as ushers and security guards. Hunter subsequently returned to the stage, drew a revolver, and was stabbed to death by Hells Angel Alan Passaro.