A newspaper carrier discovered the infant at around 4.30am on Monday when he was on his route in Madera.
The woman asked the man if he could take her child, deputies said.
He initially thought it was an animal until he got closer before realising it was a newborn baby.
As he got closer, he was horrified to realize it was a baby lying on its back, crying.
The little girl was in onesie pyjamas with her umbilical cord still attached. Although the baby is in good condition, she was admitted to the NICU.
The CHP says the infant was dressed in a soiled onesie in 30-degree weather. The pair put the infant in the woman's auto where the heating was on, and discovered the uncut umbilical cord.
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The baby was taken to the Neonatal Intensive Care Unit at Valley Children's Hospital for treatment and is doing well, according to a statement by Madera County Sheriff's Office.
Now authorities are on the hunt for the baby's mother. "This female got out of her vehicle, asked the man if he could help her and asked him to take her child", Madera County Undersheriff Tyson Pogue told reporters Monday. She asked him if everything was ok - and Fuentes responded that he just found a baby.
The woman was described by Madera County Sheriff's Office as a "Hispanic female adult, possibly in her early 20's".
Pogue said the situation was inexplicable and also noted that any newborn infants can be safely surrendered at any designated "safe surrender site" - a fire station or hospital - without any questions asked or the mother facing any charges.
If you have any information on this incident, please call the Madera County Sheriff's Office at 559-675-7770. The sites are typically hospitals or fire stations.
A California Highway Patrol officer holds a newborn baby who was found on a road.