Officers responded to a ShotSpotter gunshot detection system alert at 960 S. 47th St. around 8:45 p.m.
The victim was dropped off at a hospital while police were still en route, and she later died of her wounds.
The victim has been identified as 20-year-old Alexandrea Sweitzer, according to the Contra Costa County coroner's office.
Investigators believe that an argument at the park may have escalated, leading to the shooting.
Police are asking anyone with additional information to call Detective C. Decious at (510) 621-1747.