Abstract The 2.4-km-long Proffit Mountain flood scour formed when the upper reservoir of the Taum Sauk Power Plant, a reversible pumped electric storage facility, failed on 14 December 2005. Approximately 1.3 billion gallons of water drained from the reservoir in roughly 12 minutes, scouring a small tributary on the west flank of Proffit Mountain to bedrock and depositing debris in the valley floor and in the valley of the East Fork of the Black River. The stratigraphic succession exposed includes Mesoproterozoic Taum Sauk Rhyolite and Munger Granite, Cambrian conglomerate and dolomite and flood deposits. The site provides a unique opportunity to study a landscape-scale outcrop.