Officers responded to reports of a multi-vehicle crash on northbound Vasco Road south of Camino Diablo at 12:01 a.m., CHP Officer Tom Maguire said.
A woman was driving south in a Dodge Neon when for unknown reasons she crossed a double-yellow line and veered into northbound traffic, Maguire said.
The woman sideswiped three vehicles before her car spun out and was broadsided by a 24-year-old Discovery Bay man driving a Ford Focus, Maguire said.
The woman was declared dead at the scene. No one else was injured in the crash.
Northbound lanes on Vasco Road were shut down for about three hours.
It has not been determined if alcohol or drugs were a factor in the crash.