Beneath the turf lies a mixture of burnt stone and charcoal, the characteristic signature of a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland. The crescent or horseshoe shape is typical of the form: the hollow at the centre once held a trough, usually timber-lined or cut into the earth, which was filled with water. Stones were heated in a fire nearby and dropped into the trough until the water boiled, and the discarded, fire-cracked stones were piled to either side over time, building up the distinctive curved mound that survives today.

Fulachtaí fia are among the most common archaeological monuments in Ireland, with thousands recorded, yet individual examples rarely attract much attention. The one at Loughanboy was documented as part of a survey of the Ballinrobe district, covering the areas around Lough Mask and Lough Carra, compiled by D. Lavelle and published in 1994 by the Lough Mask and Lough Carra Tourist Development Association. The marshy ground surrounding the site is no accident of preservation; fulachtaí fia were almost always positioned close to water sources, whether streams, springs, or boggy hollows, both for practical access to water and because such low-lying ground was of limited agricultural value and so escaped later ploughing or development. The charcoal within the mound hints at the repeated fires that fed the process, though without excavation it is impossible to say how intensively or over how long a period this particular site was used.