A cairn, in the Irish archaeological context, is typically a mound of stones heaped over a prehistoric burial or used as a landscape marker, and this one belongs firmly in that ancient tradition. What gives it a quietly unsettling quality is the evidence of human interference written into its surface: it has been dug into in many places, and there is a strong suspicion that the stone field fence enclosing it was partly built from the cairn's own material, robbed out over generations by farmers who saw good building stone sitting unused on their land.

The mound is delimited at its base by twenty-one boulders, which likely once formed a kerb defining the cairn's original edge, a common feature of prehistoric monuments in the west of Ireland. According to a 1994 archaeological survey of the Ballinrobe district, compiled by D. Lavelle and covering the broader area around Lough Mask and Lough Carra, the cairn sits within an enclosure of stone field fencing, and that fence may owe its existence, at least in part, to the monument it surrounds. There is a certain irony in that: the stones stripped from a prehistoric burial site repurposed to wall off the very ground from which they were taken. The townland name, Carn, simply reflects what was always the most obvious thing about this place.