A good Samaritan reported finding an infant at a business parking lot in the 11600 block of Washington Boulevard in Whittier on Saturday around 6 p.m.
Sheriff's deputies with the Pico Rivera station responded and found the newborn still alive.
The infant was transported to a local hospital and is expected to survive.
Deputies investigated and spoke to a woman in the area who was believed to have more information.
The woman, believed to be the child's mother, was arrested on felony child endangerment charges.
Her identity has not been released.