At least 100 people were arrested and dozens hurt when a spring-break party dubbed Deltopia got out of hand Saturday night in Isla Vista in Santa Barbara County, authorities said.
The unrest lasted for several hours as partygoers and police clashed.
According to Channel 3 in Santa Barbara, authorities used tear gas, pepper spray, flash-bang grenades and foam projectiles to control the crowd.
The problems were captured in photos on social media:
About 15,000 people attended Deltopia, a party near UC Santa Barbara, when a disturbance broke out about 9:30 p.m. in the 6700 block of Del Playa Drive, according to a statement from the Santa Barbara County Sheriff's Department.
The incident began when a UCSB police officer was struck in the head with a backpack containing bottles of alcohol, according to the statement. When an arrest was made, the crowd became unruly.
Several people threw rocks and bottles at officers and an unlawful assembly was declared, according to the sheriff's statement. During the melee, street signs were ripped down, small fires were set and sheriff's vehicles were damaged, authorities said.
Ventura County law enforcement was also dispatched to the scene to provide assistance, officials said.
After several hours, authorities were able to disperse the crowd and restore order. At least five deputies were injured, including one who was hit in the face with a brick, and dozens more people were sent to the hospital for related injuries, authorities said.