This paper reviews the historic and accepted explanations requiring millions of years of erosion for an unusual geological feature, the granite Chaos at Huelgoat in central Brittany, where huge granite boulders are jumbled together along a narrow valley. The geological evidence from the site does not support such a gradualist explanation, and is consistent instead with a sudden catastrophic flood of water such as might be caused by an outburst flood. The present geography of the site shows that a lake of sufficient size could once have been retained in the valleys upstream of the Chaos, by a natural dam across the present location of the Chaos. Archaeological evidence from nearby Palaeolithic, Mesolithic, and Iron Age sites coupled with Roman history points instead to an event in the time range 3,000–4,000 B.P. Supposedly anomalous radiocarbon dates, once adjusted in line with errors such as have been found in radiocarbon dating in the wider region, support this analysis, but call into question the currently accepted dating of the Palaeolithic and Mesolithic eras. This suggests that the events at this location were much more recent and possibly contemporary with Bronze Age cultures in the Mediterranean region.