A sheriff's deputy found a Toyota Corolla crashed in a vineyard while driving on Shields Avenue, west of Goldenrod Avenue, just before 5:30 am.
Officers say the deputy found the driver unresponsive. He was taken to Community Regional Medical Center, where he later died.
The victim is in his 40s, but his name hasn't been released.
Officers say the driver may have suffered a medical emergency right before he crashed. They added that he was not wearing a seatbelt.
California Highway Patrol officers have taken over the investigation.