The incident happened on the 2400 block of Angela Street at about 7:45 p.m. on Tuesday.
Authorities say the child fell 15 feet onto the concrete below. Officials say the child sustained trauma and was airlifted to an area hospital for treatment.
According to Pomona police, the girl got onto the balcony wall of her family's apartment by climbing a pile of trash several feet high.
Officials with the Los Angeles County Department of Children and Family Services are investigating living conditions at her home.