What lies beneath and within it, however, marks it as a survival from prehistoric Ireland: a fulacht fia, one of thousands of ancient cooking or processing sites scattered across the Irish landscape. The term refers to a type of monument typically consisting of a horseshoe-shaped or circular mound of fire-cracked stone, built up over time as heated rocks were used to boil water in a nearby trough or pit. The stones, fractured by repeated heating and sudden cooling, were discarded into a growing mound beside the trough, and it is exactly this characteristic debris that gives fulachtaí fia their distinctive form.

The Ballagh example was recorded by MacMahon in 1991 and presents a well-defined circular mound measuring 12.2 metres in diameter at its base, rising to between 0.4 and 0.7 metres in height. The top of the mound is flat and slightly concave, with a diameter of around 7 metres, and heat-shattered stone remains visible at the surface. A drain filled with hard core lies to the south-west of the mound, suggesting some management of water in the area, which is consistent with the water-dependent function these sites are thought to have served. MacMahon also noted a second fulacht fia in the same townland, indicating that this stretch of Clare countryside saw repeated, perhaps sustained, prehistoric activity of this kind.