Adam Luzzi, 18, of Fairfield, was driving a 1984 Honda Civic south on Monticello Road, part of state Highway 121, about a mile south of Circle Oaks Drive, when the car went off the road and down an embankment around 1:30 p.m., CHP Officer Garrett Ray said.
The Honda overturned and landed on its roof in a creek, trapping Luzzi and passengers Antonio Del Castillo, 17, of Fairfield, and Cody Dalen, 19, of Vallejo, Ray said.
A CHP sergeant on patrol in the area came upon people who had been caravanning with the occupants of the Honda, and who had stopped at the crash scene, Ray said.
The sergeant climbed down the embankment before fire and emergency medical personnel arrived, Ray said.
Dalen was pronounced dead at the scene, and Luzzi suffered major injuries, Ray said. He was taken to Queen of the Valley Medical Center in Napa and was in stable condition this morning, hospital spokeswoman Vanessa De Gier said.
Del Castillo suffered moderate injuries and was also taken to Queen of the Valley Medical Center but was not in the hospital this morning, De Gier said.
Ray said there is no indication alcohol was a factor in the crash, but that speed may have played a role.