This is a comprehensive study of fluid flow into a cooling pluton along its metasomatic, hydrothermal contact with carbonate wallrock. We took a multi-method approach (SIMS, EPMA, LA-ICP-MS, SEM, laser fluorination, and fluid inclusion assemblage thermometry) to trace oxygen isotope and major and trace element chemistry across garnet crystals in a late Cretaceous, sub-volcanic paleohydrothermal system in the south central Sierra Nevada. The skarn garnets at White Chief canyon, the focus of our study, are nearly pure andradite and low d18O, both unusual occurrences in Sierran skarns, and a relatively unstudied realm of skarn garnet occurrence in general. The fluid chronology revealed by this isotopic work advances the detailed understanding of variability over time and space at a hydrothermal contact.