the top of the 2x4 on top of the wheel wells is 7" above the floor of the bed. i'll try to find a photo.I just happened to be reading the owners manual yesterday and it says that if you set the tailgate in the "1/2 open" condition to haul things like plywood and such then you need to add some support in the bed. It suggests laying a 2X4 across the wheel humps, using the convenient depression that they added just for that purpose. It then says that the depression in the sidewalls, between the wheel wells and the tailgate will hold two 2X4s stacked on edge. This supposedly provides a level "rack" with the tailgate - based on that I would say the wheel wells are somewhere around 10 inches tall?
i was wrong, 6 and 5/8" is what I measured from bed floor to top of 2x4.