Wash, dry, light polish (I use PO85RD, but anything will work). Mine look like that after road trips too.
Looks like an 08+ Suby rack. I believe that it's aluminum. If so, then I would wash and use some metal polish. Looks like water spots. Or polish with compound.
Try some metal polish with 0000 steel wool. If that doesn't get them off, then have them painted and seal them up with wax!