It is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, typically dating from the Bronze Age. The name, loosely translated as "cooking pit of the deer," refers to the method believed to have been used at such sites: water was heated in a trough by dropping fire-cracked stones into it, the stones were discarded after use, and over generations the accumulated debris built up into the characteristic horseshoe or oval mound of dark, burnt material that survives today.

The mound at Gortdonaghmore measures roughly 24 metres on its northeast to southwest axis and about 10 metres across, reaching a height of 0.35 metres. It is not a uniform shape; the mound increases noticeably in both height and width towards its northeastern end, suggesting that activity was concentrated in that direction, or that material accumulated there over a longer period or through repeated use. The presence of a drain along the southeastern edge is itself consistent with the typical setting of fulachtaí fia, which are almost invariably found near water sources, a practical necessity given that the entire process depended on a ready supply.