Units responded to reports of a rollover crash on northbound Highway 85 north of Winchester Boulevard at about 3:45 p.m., according to the CHP.
Gilroy resident Stacy Lonnberg, 51, had been driving a 2002 Toyota Tacoma in the far left lane.
Lonnberg tried to make an unsafe lane change at a high rate of speed, the CHP said.
Her vehicle sideswiped a 1998 Chevy Silverado in the next lane, causing her to lose control.
The Toyota overturned several times, coming to rest on its wheels in the northbound lanes, the CHP said.
The passenger in the Toyota's rear left seat was ejected and pronounced dead at the scene. She was later identified as Tiffany Gillette, 26, of Fremont, the CHP said.
A passenger in the front of the Toyota was partially ejected and taken to a hospital with major injuries. He was later identified as Frederic Lonnberg, 67, of Gilroy.
Lonnberg was declared dead at the hospital at 10:45 p.m.
A 1-year-old boy also traveling in the Toyota was not injured, the CHP said.
The driver of the Chevrolet pulled over the right shoulder and was not injured.
Stacy Lonnberg was arrested for driving under the influence of drugs and alcohol and arrested for DUI and felony vehicular manslaughter, according to the CHP.