Guys I need to find out what this is- it's also on my wooden bed racks
The pictures seem to be showing corrosion of aluminum. The finish on the aluminum, whether that be a clear anodize or other lacquer or enamel coating, has failed in spots and is allowing aluminum oxide to form. As you can guess aluminum oxide is white in color.
The white outer circles appears to me to be white rust, which is a term for corroded zinc; zinc is the protective layer of galvanized steel. The inner darker disks... probably indicate exposed steel (no longer covered by zinc), possibly slightly corroded as well.