Abstract: The windrow pickup header of a forage harvester is supported at least in part by gauging means that senses rises and falls in the terrain in front of the header to swing the latter up and down to accommodate such unevenness in the terrain. Long, generally fore-and-aft extending arms on opposite sides of the header have caster wheels at the forwardmost, free ends thereof and have inturned sections at their opposite ends which are fixed to the header adjacent the top of the latter and spaced substantially above the swinging axis of the header so that any rearwardly directed force applied to the caster wheels is transmitted through the arms to the top of the header to swing the same upwardly to overcome the force, rather than causing the header to buckle downwardly under as a result of the force application.