The GANGOTRI mission concept would investigate in situ the geologic origins of midlatitudinal Martian glaciers, as underlain by Amazonian climate evolution, by riddling the ice with a hybrid thermo-mechanical drill for deep englacial sampling. GANGOTRI would use regolith compositional measurements to characterize ice-regolith interaction, and stable isotope measurements to characterize fundamental exchange processes of major ice reservoirs. Meanwhile, geophysical observations would cross-calibrate composition.