More than 18,000 people braved triple digit temperatures Saturday to attend the annual Aftershock Concert at Sacramento's Discovery Park.
Many from out of state were surprised at the heat.
"This whole heat, this southern heat thing is new to me," Selene Tyndale from Quebec, Canada said.
However, many came prepared.
"I do have sun block on, and I ordered this battery-operated clip online at amazon," Gina Perry from Santa Barbara said.
She said she learned her lesson after attending last year's concert without the fan.
In case people rocked out a little too hard, concert promoters set up a mobile hospital on site.
"On site, they can do virtually everything, other than X–rays. They can suture, they can put in an IV, everything that needs to be done to help people re-stabilize and more often than not, return to the audience and continue to have fun," concert producer, Danny Hayes said.
The medical team is called "Rock Med," a team of volunteer doctors, nurses, and EMTs that specialize in concert related medical emergencies.
The San Francisco company said heat exhaustion is the number one diagnosis on hot days, so they recommend people stay hydrated.
The group is funded solely on donations, and offer their services, free of charge.
The Aftershock Concert continues Sunday. The promoters expect a total attendance of more than 37,000 people in two days.
Tickets for Sunday are $65 per person. Gates open at 11 am, and close at 10 pm.