Aftershock Festival is not just California's biggest rock festival, but one of North America's premier music festivals for all different genres of rock music, including hard rock, nu metal, grunge, heavy metal, death metal, punk rock, and alt-rock. Since 2012, it's been held annually each fall in downtown Sacramento, CA at Discovery Park. Aftershock began back in 2012 as a single-day festival, before expanding to two days in 2013 and then three days in 2019. As of 2021, the festival that starts on October 7th will span four days for the very first time, giving fans the opportunity to rock out from Thursday all the way through Sunday night. There have been some incredible acts that have performed at Aftershock over the years, including headliners like Weezer, Rob Zombie, Tool, Slipknot, Nine Inch Nails, Ozzy Osbourne, and many more.