The accident happened around 6:15 p.m. near Tefft Street in Nipomo.
The California Highway Patrol says a Chevrolet Silverado driven by a 29-year-old San Diego man cut off a Toyota 4Runner driven by a 20-year-old woman from Santa Maria.
CHP says the driver of the 4Runner lost control while trying to avoid a collision with the Silverado.
Her vehicle then overturned several times, hitting a Hyundai Sonata driven by a 35-year-old woman from Orcutt.
Officers say the driver of the 4Runner was not wearing her seatbelt and was ejected from her vehicle. She was taken to the hospital with major injuries.
The driver of the Sonata received minor injuries, and the driver of the Silverado was not injured.
The crash is under investigation.