"Fullerton Fire responded back to the apartment and found the newborn baby boy deceased," said Sgt. Andrew Goodrich of the Fullerton Police Department.
An autopsy later determined the cause of death was a blunt force injury to the head and asphyxia while submerged in water.
Police believe Valderrama was trying to hide the pregnancy from her parents and was at full term when she gave birth to the child.
Valderrama is being charged with murder, child endangerment, and inflicting great bodily injury while committing a felony. She was booked at the Fullerton Jail, and later taken to Orange County Jail.