An assemblage of pyroxenite, peridotite, and mafic granulite xenoliths contained in the toe of a 10 Ma trachybasalt flow remnant overlying Late Cretaceous granitoids indicates the presence of a mafic-ultramafic complex beneath the Sierra Nevada batholith. Olivine-free pyroxenites that include orthopyroxenites, websterites, and clinopyroxenites are dominant. Primary igneous textures are displayed by some pyroxenites, but commonly are masked by recrystallization. Fe-rich harzburgites and lherzolites are rare. A few of the ultramafic xenoliths contain ovoid opaque patches that are apparently pseudomorphs after garnet and have pyralspite garnet compositions. A pressure corresponding to a lower crustal depth of approximately 40 km has been determined from two of these xenoliths using a garnet-orthopyroxene geobarometer. Abundant mafic granulites can be subdivided into those containing 12 per cent or less A₁₂O₃ and chemically gradational with pyroxenites and others containing more than 15 per cent A₁₂O₃ and showing considerable scatter on oxide variation diagrams. The high-alumina granulite xenoliths have relatively low ⁸⁷Rb/⁸⁶Sr but high ⁸⁷Sr/⁸⁶Sr, whereas low-alumina and ultramafic xenoliths have a wide range of ⁸⁷Rb/⁸⁶Sr, but lower ⁸⁷Sr/⁸⁶Sr; the isotopic data indicate an age for the complex roughly the same as that of overlying granitoid plutons. However, the granitoids have initial ⁸⁷Sr/⁸⁶Sr ratios intermediate between the high-alumina and ultramafic xenoliths, suggesting that they may have resulted from mixing of basaltic magma, represented by the ultramafics, and crustal materials, with subsequent crystal fractionation. The trachybasalt may represent a partial melt of the ultramafic rocks. Rocks analogous to the Chinese Peak xenoliths are exposed in the Giles complex of central Australia, a series of several deformed layered mafic and ultramafic intrusions, emplaced in a granulite facies terrain. Contemporaneous development of mafic-ultramafic complexes and the Sierra Nevada batholith may explain the present day thick (˜ 50 km) crust in this region