This is a fulacht fia, a type of prehistoric cooking site found in extraordinary numbers across Ireland, typically Bronze Age in origin, and almost always located near a reliable water source. The mound itself is not rock or rubble in any obvious sense; it is the accumulated debris of repeated use, built up over time from heat-shattered stone discarded after each firing. The characteristic horseshoe shape comes from the way that waste material was heaped around three sides of a central working trough, leaving one side open for access.