A fulacht fia is a type of ancient burnt mound, found in considerable numbers across Ireland, and typically consisting of a crescent or horseshoe-shaped heap of fire-cracked stone and charcoal left behind after repeated use of a water-filled trough heated by dropping in fire-hot stones. The process was simple but effective, and these sites cluster reliably on wet or boggy ground, which is precisely the kind of terrain occupied by the example at Ballynaboul.

When the Castleisland District Archaeological Survey recorded the site in 1985, what they found was a roughly D-shaped mound measuring approximately 16 metres northeast to southwest and 11.5 metres southeast to northwest, rising to a modest 0.65 metres in height. The mound was composed of burnt material, and surveyors noted a possible trough area to the northwest, where the ground remained conspicuously waterlogged, consistent with the functional requirements of a fulacht fia. That waterlogging, so characteristic of these sites, is itself part of the reason so many have survived at all, preserved beneath layers of peat and damp soil. At Ballynaboul, however, survival proved incomplete. Aerial imagery captured between 2011 and 2013 showed no surface remains visible, suggesting the mound had by then been levelled, ploughed out, or simply absorbed back into the saturated landscape that had sheltered it for millennia.