Police say the GMC minivan was traveling on the northbound lanes of the 110 Freeway connector to the 5 Freeway when it rolled over around 12:20 a.m.
The vehicle reportedly veered to the right of the roadway and struck a raised concrete wall. The vehicle then overturned and skid on its right side until coming to rest in the No. 2 lane.
Four people were fully ejected from the vehicle, three of them fatally.
Katie Davila, 12, Abigail Romero, 19, and Abigail Estrella, 37, were pronounced dead at the scene. All three were residents of Lancaster.
The four injured were transported to Los Angeles County + USC Medical Center.
Among the injured victims was as a 36-year-old father, his 4-year-old daughter and 13-year-old son. All three were released from the hospital Saturday afternoon. The driver, identified as a 55-year-old man, was treated for minor injuries.
The crash shut down the No. 1 and No. 2 lanes in the area until 3:30 a.m.
No further details were released. The cause of the crash was still under investigation.