It measures roughly 28 metres north to south and 30 metres east to west, rising just over a metre above the surrounding pasture. That description, modest as it sounds, marks it out as a fulacht fia, one of the most common prehistoric monument types in Ireland and one of the least understood.

A fulacht fia is essentially the debris left behind by an ancient cooking or heating site. The typical arrangement involved a trough dug near a water source, which would be filled and heated by dropping fire-cracked stones into it. Over repeated use, those shattered stones accumulated into the horseshoe-shaped mounds that survive across the Irish landscape today, often close to streams or boggy ground exactly as here. The Ballynoe example sits on the western bank of a stream, which fits the pattern precisely. The mound appears to have been clipped on its northern side, probably by the cutting of a drainage channel at some point after the site fell out of use, which accounts for what is described as truncation rather than a naturally rounded edge.