At 3:13 p.m. officers went to the 2800 block of Valencia Way where they found the victims.
Police said they found a 47-year-old woman and a 22-year-old man suffering from gunshot wounds.
The woman was pronounced dead by paramedics. The man was taken to a hospital and is expected to live.
Police said detectives are still determining whether one or both victims were the intended targets of the shooter or shooters.
Anyone with information about the shooting is asked to call the Police Department's investigations division at (510) 215-3150 or the West Contra Costa Crime Stoppers tip line at (510) 799-8255.
All callers can remain anonymous.