A 23-year-old San Jose resident died in a car crash Monday afternoon on southbound Interstate Highway 280 near Portola Valley, according to the California Highway Patrol.

The crash was reported around 2:30 p.m. on southbound Highway 280 north of Alpine Road, not far from the Stanford Dish.

According to the CHP, a white 2006 Toyota Tundra was traveling south when, for unknown reasons, the motorist drove onto the right shoulder and about 20 feet up an embankment, crashing into a tree before the car came to rest between two lanes of traffic a half-mile north of Alpine Road. A majority of the damage was on the truck's roof, most of which came off, and left side, CHP Officer Art Montiel said.

The driver, a 23-year-old San Jose woman who was the only person in the car, died at the scene, Montiel said. She was found wearing her seatbelt.

Investigators are looking into what caused the crash, including whether speed, drugs or alcohol played a role, according to Montiel.

She was identified as Marley Marie Gregory, the San Mateo County Coroner's Office said.

The crash blocked three left southbound lanes of Highway 280 at Sand Hill Road, backing up traffic to Sand Hill Road, Montiel said. All lanes were reopened as of 5:35 p.m.

Anyone who witnessed the crash is asked to call CHP Officer Adrian Lopez-Martinez at 650-369-6261.