LOS ANGELES – One man and two women died after attending a weekend outdoors rave in Fontana headlined by Ice Cube, Major Lazer and dozens of other hip hop and electronic dance music performers, officials said Monday.

The three were among nine people hospitalized during last weekend’s Hard Summer Music Festival, San Bernardino County sheriff’s spokeswoman Jodi Miller said. More than 146,000 people attended the Saturday-Sunday event, according to Hard Summer organizers.

The victims were identified as Derek Lee, 22, of San Francisco; Alyssa Dominguez, 21, of San Diego; and Roxanne Ngo, 22, of Chino Hills, according to the San Bernardino County coroner’s office

Lee and Dominguez died early Sunday morning and Ngo died early Monday morning, authorities said. The causes of death were under investigation.

“We were deeply saddened to learn about the deaths of three people who attended the festival this weekend,” Hard Summer spokeswoman Alexandra Greenberg said in a statement. “While the causes of the deaths have not yet been determined, we ask everyone to keep them in their prayers. Our sincerest thoughts and condolences are with their family and friends.”

Hard Summer was moved to Fontana’s Auto Club Speedway this year after two young women died of drug overdoses at last year’s event at the Los Angeles County Fairgrounds in Pomona.

The parents of 19-year-old college student Katie Dix recently sued event promoter Live Nation, Los Angeles County and others over Dix’s death, which authorities blamed on multiple-drug intoxication.

The other death, of 18-year-old UCLA student Tracy Nguyen, was from an Ecstasy overdose.

Ecstasy is a popular drug at raves where concertgoers use it to enhance the musical experience. It can also lead to dehydration, however, causing concern among medical officials that its use in hot, crowded quarters where people sometimes dance for hours can lead to collapse and sometimes death.

Temperatures in the Fontana area, 50 miles east of Los Angeles, have been in the 90s.

Amid mounting concern about overdoses at raves, some venues have banned them.

The popular Electric Daisy Carnival was moved to Las Vegas after the Los Angeles Memorial Coliseum stopped holding raves following numerous drug overdoses and other problems. The Cow Palace in San Francisco banned them in 2010.

Hard Events, founded in 2007 by music executive Gary Richards who also performs as DJ Destructo, has grown dramatically in recent years and branched out to include hip hop as well as electronic dance music, or EDM.

Ahead of last weekend’s rave, Hard Summer officials posted a lengthy list of warnings on its website for people attending this year’s event. They urged people to stay hydrated, take regular breaks from dancing and monitor themselves for any signs of heat exhaustion.

The warnings also said illegal drugs would not be tolerated and that people bringing prescription drugs would have to check them with medical authorities.

“Our number one main concern is your safety,” the warning said.