A suite of garnet-bearing xenoliths that is dominantly composed of olivine, clinopyroxene, and garnet, from Oahu, Hawaii is discussed. All the minerals are in Mg# equilibrium with each other. High Fe/Mg of constituent minerals, high TiO2, Al2O3, Na2O of cpx, and low Cr-garnet preclude these xenoliths from being residues of partial melting. Combined petrography, mineral chemistry, and high-pressure liquidus phase equilibria indicate that these xenoliths are high pressure cumulates and originated as products of magma fractionation at a depth of >100 km, corresponding to the uppermost part of the asthenosphere. These depth constraints are about 15 km more than the seismically detected lithosphere-asthenosphere boundary. It is proposed here that the top of the asthenosphere beneath Oahu, Hawaii is a network of magma chambers where considerable amount of magma ponding and subsequent fractionation takes place.