Organizers were forced to suspend the event this afternoon for more than two hours because of severe weather.
Tens of thousands of concertgoers took shelter in parking garages.
Organizers say it was unfortunate, but that safety was paramount. The estimated 100,000 concertgoers took the evacuation order in stride.
Crowds were allowed back into the venue after the worst of the powerful thunderstorm had passed and police and concert organizers had inspected the park for any damage.
Organizers posted a reshuffled Saturday lineup that added a half-hour to the night's events, which are scheduled to culminate with the Red Hot Chili Peppers performing on the main stage. The three-day event ends tomorrow.
It was only last summer that storm-driven wind gusts knocked down heavy stage rigging at the state fair in Indiana, killing seven people and injuring dozens of others.