The person killed when two cars collided east of Gustine on Monday afternoon was a 69-year-old woman from Stevinson, authorities said.
According to the California Highway Patrol, Guillermo Ruiz, 32, of Morgan Hill was driving a 2006 Honda Accord west on Highway 140 near Mud Slough when the accident occurred at 4:07 p.m.
The Stevinson woman, whose name was not released, was driving a 1997 Honda Civic in the opposite direction.
For an unknown reason, the CHP said in a news release, Ruiz turned the Accord to the right, driving onto the right shoulder of the road and striking the guardrail of the Mud Slough bridge.
Ruiz turned back to the left, and the Accord went across the road, directly into the path of the Civic. The cars collided head-on and came to rest in the eastbound lane.
The woman was pronounced dead at the scene. Ruiz was taken to Doctors Medical Center in Modesto with minor injuries.