Abstract: This invention relates to a grain cart having a downwardly and inwardly tapered hopper for temporarily storing grain, an auger mounted to an outer, forward portion of the cart's hopper is adapted for unloading grain from the cart. An interface housing mounted to the outer portion of the cart's forward inclined wall and disposed over an aperture in the wall is coupled to a lower end of the auger. Grain discharged from the hopper under the influence of gravity enters the interface housing and is removed from the housing by the auger for discharge into another vehicle such as a truck. The interface housing is removably mounted to the outer surface of the hopper, such as by bolts, to facilitate removal and repair of the auger, and to simplify grain cart design and manufacture. An angle drive gearbox couples the auger shaft to the power take-off unit of a tractor pulling the grain cart for driving the auger.