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The Heise volcanic field is the second youngest caldera complex of the Yellowstone–Snake River Plain province (USA) and represents a polycyclic caldera system with rhyolitic volcanism extending over more than 2 Myr. The products of the Heise volcanic field include four regionally extensive ignimbrites, including the Blacktail Creek and Kilgore tuffs, which both have volumes estimated at >1000 km ³ , separated by sequences of smaller volume tuffs, lavas and sedimentary deposits. Rhyolites from the Heise volcanic field are both normal-δ ¹⁸ O and low-δ ¹⁸ O, making it a key locality for investigating rhyolite petrogenesis. However, the occurrence of abundant young basaltic lava has limited our ability to fully characterise this volcanic centre, particularly in terms of post-caldera volcanism. Here we describe rhyolitic samples from both a >700 m thick section of drillcore within the Snake River Plain and the exposed …