The cairn measures twelve metres across and rises to between 0.7 and 2.6 metres in height, its uneven profile suggesting either deliberate construction or centuries of gradual disturbance. A cairn, in the broadest sense, is simply a deliberate accumulation of stones, but the term covers everything from prehistoric burial monuments to practical boundary markers, and here the distinction matters because this one may belong firmly to the latter category.

Unlike the more elaborate prehistoric cairns found elsewhere in Ireland, which typically enclose a burial chamber and are edged with kerb stones to define their perimeter, this structure shows none of those features. The working theory is that it was raised to mark the boundary between townlands, those ancient divisions of land still used as place-name references across Ireland today. What makes the location particularly interesting is that it does not sit alone. A second cairn lies immediately to the south, and a third sits roughly twenty-five metres to the north-east, suggesting this high ground on Black Rock Mountain once served as a meaningful line in the landscape, a place where administrative or territorial edges were made visible in stone.