In California, it depends on the vehicle doing the towing, whether or not it has to go through the scales.
If your truck is a cab/chasis truck (did not come from the factory with a pickup bed installed on it as new) over 10,000 lbs GVWR, unless it has been upfitted with a permanent motorhome body on it, it has to go through the scales, regardless of what kind of trailer you're towing.
Pickups are not allowed on the scales in California, unless the truck is used to haul freight commercially and displays a US DOT number on the truck.