OCEANSIDE, Calif. -- An autopsy is being performed Sunday on a young woman who died after a party and under mysterious circumstances in Oceanside, authorities said.

Elizabeth Butler, 20, was found unconscious and not breathing at about 10:25 a.m. Saturday in a residence in the 2900 block of Farel Street, according to the Oceanside Police Department.

An investigator with the San Diego County Medical Examiner's Office said Butler was rushed to Tri-City Medical Center, where she was pronounced dead at around 11 a.m. The cause of death was unknown so far, she said.

According to police, the Escondido resident attended a party at the Farel Street house Friday night. There were no obvious signs of trauma.