The 1.43-Ga Sherman batholith of southeastern Wyoming and northeastern Colorado is a texturally and geochemically heterogeneous intrusion that comprises rocks derived from at least four different sources. The coarse-grained, metaluminous, biotite-hornblende Sherman Granite is volumetrically the most significant unit in the batholith. It has geochemical characteristics at the extreme end of A-type suites with high Fe# > 88, high K2O wt. % (generally > 5%), molar Na/K generally 1). Field and geochemical observations are consistent with many of the porphyritic granites having formed by mixing between granitic and monzodioritic magmas and highlight the importance of magma mixing in the formation of the batholith. Mafic rocks are present in the batholith in minor quantities and include gabbro, ferrodiorite, and monzonite in addition to monzodiorite. All of the mafic rocks are geochemically and mineralogically similar to rocks from the adjacent LAC, and the gabbro presumably is derived from a mantle source similar to that for gabbroic rocks from the LAC. Geochemically distinct sodic granodiorite, which occurs in minor quantities in the batholith, represents a distinct unit likely derived from partially melted metabasalt. The rocks of the Sherman batholith record the evolution of Mesoproterozoic lithosphere in five ways: 1) gabbro records asthenospheric input of heat and mass(?) into the juvenile, Paleoproterozoic lithosphere; 2) peraluminous granite records partial melting of the Paleoproterozoic lithosphere in response to the influx of asthenospheric melts; 3) hybrid porphyritic rocks record the direct interaction of mantle-derived magma and crustal materials to produce lithosphere with intermediate characteristics; 4) Na-rich rocks record melting of metabasalt emplaced prior to or during widespread magmagenesis; and 5) the Sherman Granite records direct partial melting of juvenile lithosphere and subsidiary fractional crystallization locally accompanied by crustal assimilation.