If you are a involved in a Ontario California car accident you should always call the Ontario Police department and make a accident report. Having a police report in place will greatly reduce any footwork you may have to do to find proper car insurance information and contact information for the negligent driver. Some drivers don't always provide correct or even accurate insurance or contact information when they have been involved in a Ontario California car accident.
In some cases local law enforcement may not be able to come to the Ontario California car accident scene. If you are unable to get law enforcement to come to the accident scene you should get as much information from the other driver as possible, which would include insurance information, contact information like current address and phone number, and always get plenty of pictures of the accident scene.