This is the basic mechanics of a fulacht fia, a type of Bronze Age cooking or processing site found in enormous numbers across Ireland, recognisable by the horseshoe-shaped mounds of burnt and shattered stone left behind after centuries of use. The example at Ballynastaig was, when first recorded in December 1982, an unusually well-preserved specimen: a grassed-over mound about eleven metres in diameter, with a central depression opening to the west and fragments of burnt and cracked stone still visible at the surface.

What made the site more than a single, isolated monument was the cluster of smaller mounds around it. Three irregular rises immediately to the north-north-east and one to the south-south-east also contained burnt earth and limestone, suggesting they were connected to the main monument rather than incidental features of the landscape. Further east, sitting within the turlough itself, a second possible fulacht fia was recorded. A holy well lies roughly sixty metres to the north-north-west, and the proximity of that kind of water source, whether or not it predates or postdates the Bronze Age activity, adds to the sense that this particular patch of ground held some significance across different periods. By the time the site was reinspected in June 1992, however, no visible surface trace remained, the shallow earthworks having apparently levelled out entirely into the surrounding pastureland.