The attack happened in the Mesa parking structure near the Bren Events Center at 11:30 p.m., according to the UCI Police Department.
Police declined to release any more information about the case including whether the victim or attacker are students.
Detectives are in preliminary stages of the investigation, UCI spokeswoman Cathy Lawhon told the Times Community News.
"Our protocol in any report of sexual violence would be to provide information about all options and resources to the students," Lawhon added. "The university would investigate and respond based on the information reported and provide the students counseling services, advocacy and safety and security planning."