The woman behind the wheel of the 2007 Toyota Corolla lost control on South Mission Road in Fallbrook shortly before 12:30 a.m., according to the California Highway Patrol.
The southbound vehicle veered off of the east side of the road near Via Monserate, went down an embankment and smashed into a tree, CHP public-affairs Officer Jim Bettencourt said.
The passenger, a Fallbrook resident, died at the scene of the accident. His name was withheld pending family notification.
The 24-year-old driver was able to climb back up the slope and flag down a passing sheriff’s deputy, Bettencourt said. She was taken to Palomar Medical Center in Escondido for treatment of apparently minor injuries.
Intoxication was not believed to have been a factor in the crash, the officer said.