The California Department of Motor Vehicles allows residents to make a request for record information relating to a vehicle and its owner, including license plate numbers. According to WebLaws.org in 2011, the information is released under California Vehicle Code, Section 1810.
Per Section 1810, the DMV may permit inspection of its records concerning any vehicle. This information is public record, thus any resident is authorized to make such a request. However, the request for information includes fees and requires the full name of the person associated with the vehicle, as well as the Vehicle Inspection Number or the make and model of the vehicle.