The Ordnance Survey's six-inch map of 1837, which recorded the Irish landscape in methodical detail during the decades following the Act of Union, made no mention of this structure at all. Whether that omission reflects a surveyor's oversight or something about the mound's appearance at the time is impossible to say now, but it gives the site an odd quality, as if it only gradually announced itself to official attention.

The cairn, a prehistoric burial or ceremonial mound constructed from heaped stone rather than earth, measures roughly 26 metres across at its base and narrows to around 6 metres at the top, rising to a height of 3.7 metres on its northern side and 3.4 metres to the south. The composition is a mixture of stone and sand, which may reflect the materials available in this coastal, low-lying setting. There is some evidence that the mound was originally flat-topped rather than rounded, though quarrying on the eastern side has altered its profile and made the original form harder to read. That disturbance, presumably for building material or agricultural use at some point in the past, is a reminder of how casually significant prehistoric structures were sometimes dismantled once their original purpose had been forgotten.