Do you know either the DOT number or the ICC number which would have been posted on the side of the cab? What about a truck number, name of the trucking company, or a location that they were based from, which should have been on the door or the side of the cab? Maybe Michael Banks can help you with California trucking companies. What city or town was the truckline from? What color was his tractor and trailer. Was the trailer a dry van, a reefer, a flatbed, or a tanker? What kind of tractor, if you know?
Try the US Department of Transportation website.
If you know either the ICC-MC number or the USDOT number it will be fairly easy to find the company. A truck number or a trailer number, where this happened, and the date this happened would be a big help. How old was this guy, how big was he, did he wear glasses or have gray hair or a beard? Do you know his name or CB name.
"We stay here, we die here. We've got to keep moving". Trucker Mark