Officials with the Merced Police Department say the Hayward Police Department in Alameda County contacted them about eight-year-old Sophia Mason.
She was last seen on February 10 in the Merced area.
Mason is from Merced but has been to Hayward and other cities in Southern California with her mother. Investigators say Mason's mother is currently in custody.
No further information about the investigation was immediately available.
Authorities are asking anyone with information to contact the Merced Police Department.