The crystalline core of the North Cascades arc records the Cretaceous to Paleogene history of magmatism, deformation, and crustal growth along a segment of the North American Cordillera. The Nd isotopic compositions of granitoid plutons that intrude the Cascades core are a product of their source regions, and they provide probes of the crustal architecture. We present Sm-Nd isotopic data from 96 Ma to 45 Ma plutons and meta-igneous and metasedimentary terranes across the Cascades core. Sm-Nd data from all metamorphic terranes, excluding the much younger ca. 73 Ma Swakane terrane, yield mid-Cretaceous ε_Nd values that range from +8.5...