Officers and firefighter-paramedics responded to a call shortly after 10 p.m. to Memorial Park at 85 East Holly Street, where the baby was pronounced dead, the Pasadena Police Department said in a statement.
The grim discovery was initially made by maintenance staff who were preparing to clean the restroom and then called police, according to authorities.
Los Angeles County coroner officials arrived at the scene and removed the body of the child, which "appears to have been full-term," the police news release said.
The cause of death is under investigation.
Anyone with information about the case is asked to call the Pasadena Police Department at (626) 744-4241. Anonymous tips may be submitted to Crime Stoppers at (800) 222-TIPS.