The invention relates to a unique self propelled vehicle capable of transporting massive loads over natural terrain, such as the loading and transporting whole trees from their growing site to a processing station. The invention provides a vehicle having an elongated rigid frame element supported by two spaced sets of quad wheel assemblies, with each assembly permitting movement of individual wheels about both a roll axis parallel to the longitudinal frame element and a pitch axis transverse to the frame element. An operator's platform is adjustably mounted on the forward portion of the rigid frame structure for vertical movements and may carry with it a boom having means on its free end for severing and engaging whole trees or lifting massive objects to deposit same in cradles or a body mounted on the rigid frame element. Power actuated mechanisms are provided for rotating each wheel, steering each wheel, moving the operator's platform vertically to any desired position, actuating the loading boom, and tilting of the longitudinal frame element to maintain the horizontal plane of the operator's platform, to unlaod a stack of trees carried by the cradles or to lift an end of a quad wheel assembly walking beam. In the event that any wheel becomes inoperative a detachable linkage is provided to anchor the affected wheel in an elevated position as to permit the vehicle to be moved under its own power to a repair station. Power for all such operations is supplied from a power source adjustably mounted for vertical movements on the rear end of the elongated rigid frame element.