It is, in fact, the remains of a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically Bronze Age in origin, and almost always associated with a nearby water source. That last detail makes this particular example quietly puzzling: there is no stream immediately at hand.

A fulacht fia generally works on a simple principle. A trough is filled with water, stones are heated in a nearby fire and dropped into the trough to bring the water to a boil, and the cracked, spent stones are thrown aside, accumulating over time into the horseshoe-shaped mound that is usually the most visible surviving feature of the site. At Cartrún An Phóna, the boulder-defined area measures roughly 4.5 metres east to west and 3 metres north to south, with the adjoining mound reaching up to 2 metres in height and around 6 metres in diameter. The mound material is composed of that characteristic shattered stone, here sandstone and some quartz, mixed with dark humic earth. The absence of a stream is not, as it turns out, necessarily disqualifying: the site sits on a slope with considerable surface run-off, which may have been sufficient to supply whatever trough or hollow was once in use. The valley also contains at least two other recorded archaeological sites, suggesting this was not an isolated or accidental presence in the landscape.