From the clutch of emerging bands that performed early in the day on the side stages through the marquee headliners that graced the main stage, the songs of summer 2013 galvanized the diehard crowd of Southern Californians through the day-long extravaganza that was highlighted by the unexpected return of a '90s alt-rock favorite with a surprising new face fronting the band.

While the Black Keys and Thirty Second to Mars were the undeniable headliners, it was the Stone Temple Pilots, who delighted the sold-out show with a surprise set of their enduring radio hits like "Vaseline" and "Interstate Love Song."

But instead of the embattled Scott Weiland at center stage, Stone Temple Pilots emerged with Chester Bennington from Linkin Park on the mic, admirably leading STP with spot-on vocals and even imitating some of Weiland's signature serpentine stage moves.

With no announcement of Bennington's presence on vocals, some audience members seemed confused by the unexpected pairing, but soon word rippled through the crowd that it was indeed the Linkin Park singer performing with STP, eliciting a barrage of camera flashes as people tried to capture the inspired pairing. The band played a number of STP hits and debuted a brand new track titled "Out of Time" which is available now as a free download exclusively at Radio.com.

The Black Keys charged through a stomping set of their down and dirty blues-rock, storming through crowd favorites like "Lonely Boy" and "Gold on the Ceiling" with a vengeance, determined to leave an impression on the already bedazzled audience.