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.
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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.