The fatal crash was reported at 9:20 p.m. on Vasco Road just north of Camino Diablo Road. A Sig-alert was issued 9:54 p.m. and canceled just less than an hour later, CHP Sgt. Diana McDermott said.
The woman in a Geo Tracker traveling northbound on Vasco Road for an unknown reason made a U-turn onto the southbound lane, McDermott said.
A red Toyota Camry going the speed limit at about 55 mph in the southbound lane then broadsided the Tracker.
The woman was pronounced dead at the scene, McDermott said. The spokeswoman did not know the condition of the Camry driver after the accident.
The woman had made the U-turn about a quarter-mile from the intersection at Camino Diablo Road and approached the southbound lane from right-hand side of the two-lane road that is separated by double yellow lines, McDermott said.
Investigators are working with witnesses and looking into factors leading up to the deadly crash, including road conditions, weather, whether the woman had been wearing a seatbelt and if drugs or alcohol were involved.