12 Summits: Summit 8: Hyndman Peak (12,009 ft)
Great Granite Uplifts

The Pioneer Mountains contain a core of Paleoproterozoic gneiss overlain by younger Proterozoic and Paleozoic metamorphic rocks. These mountains were uplifted during the Eocene and Oligocene time, when volcanic eruptions located south in the Snake River plain started to thrust these rocks upward from the mantle.