It measures roughly ten and a half metres from east to west, nearly six metres north to south, and rises only a metre from the ground. But its shape, its contents, and its position are all deliberate. This is a fulacht fia, one of the most common and least understood monument types in the Irish landscape.

A fulacht fia is, at its simplest, a prehistoric cooking site. The characteristic mound is made up of heat-shattered stones and charcoal-enriched soil, the accumulated debris of repeated firings over what may have been centuries. The method involved heating stones in a fire and dropping them into a water-filled trough to bring the water to a boil, cracking the stones in the process and leaving them discarded in a horseshoe-shaped heap around the trough. The opening of the mound at Derroograne, some 2.6 metres wide, faces south towards the stream, which would have supplied the water. This relationship between the mound and the stream is typical of the type and probably explains why the site was positioned here at all, within what is now a network of field boundaries. The monument is under gradual pressure from erosion along both arms of the crescent, which has begun to expose the shattered stone and blackened soil within.