Volcanic rocks that form the southern segment of the Cascades magmatic arc are an important manifestation of Cenozoic subduction and associated magmatism in western North America. Until recently, these rocks had been little studied and no systematic compilation of existing composition data had been assembled. This report is a compilation of all available chemical data for igneous rocks that constitute the southern segment of the ancestral Cascades magmatic arc and complement a previously completed companion compilation that pertains to rocks that constitute the northern segment of the arc. Data for more than 2,000 samples from a diversity of sources were identified and incorporated in the database. The association between these igneous rocks and spatially and temporally associated mineral deposits is well established and suggests a probable genetic relationship. The ultimate goal of the related research is an evaluation of the time-space-compositional evolution of magmatism associated with the southern Cascades arc segment and identification of genetic associations between magmatism and mineral deposits in this region.