The firefighters nicknamed her Noel.
The woman, 27, was cooperative as firefighters went through procedures for taking the baby Friday afternoon.
Officials said she didn't provide a reason for wanting to give up the child, but did say she had three other children. The baby was said to be well nourished and well cared for.
The nearly decade-old Safe Haven Law in California allows parents to give up babies up to three days old at fire stations, hospitals and other locations without fear of prosecution if there are no signs of abuse.
She was the sixth child surrendered in Los Angeles County in 2010 and the 82nd since the Safely Surrendered Baby Law was passed nine years ago, according to county statistics.
The newborn was taken to a hospital where she remained on Christmas Day.
The Associated Press contributed to this report.