One of the adults, a passenger, was the mother of the three girls. The other adult was a male friend who was driving the car. Police say the driver was speeding when he tried to avoid a car waiting to make a turn.
The accident happened just after 7 p.m. at 5th and English streets in Santa Ana. Responding officers found an upside-down car in the front yard of a residence at 2026 W. 5th St.
One of the girls was a 2 year old. The other two girls were 6 and 10 years old. The severity of their injuries was not immediately known.
Their mother was declared dead at the scene.
The cause of the accident was under investigation.
The crash also damaged a power pole, causing lines to be downed and a power outage in the area that was affecting about 1,500 customers.
Southern California Edison said they were waiting for the coroner to arrive in order to restore power.
It was earlier reported that the mother died at a hospital, but police say she was declared dead at the scene.