If your parked car rolls away and hits another unattended vehicle, you should

If you hit a parked vehicle or other property, leave a note with your name, phone number, and address inside and securely attach it to the vehicle or property you hit. Report the collision to the city police or, in unincorporated areas, to the California Highway Patrol (CHP). [Involved in a Collision; Collisions Are Not Accidents; California Driver Handbook]