A cairn is a mound of stones, often raised over a burial or used as a landscape marker in prehistoric times, and this one at Coolnatullagh has been measured at a maximum length of seventeen metres in its trapezoidal form, meaning it is roughly wedge-shaped rather than simply round. That shape, where it can still be read, places it within a tradition of monument-building that was widespread across Ireland during the Neolithic period, though the stripping away of its stones, most likely for reuse in field walls or farm buildings over many generations, has left it far harder to interpret than it once would have been.

The cairn sits within an extensive field system, suggesting that this valley has been in continuous productive use for a very long time, with successive generations reshaping the land around and sometimes at the expense of whatever came before. Carey, writing in 2008, documented the monument as trapezoidal and noted the severity of the robbing, which points to a structure that was once substantial enough to offer a useful supply of building material. The fertile valley setting, sheltered by the rising ground of Gortaclare Mountain, would have made this an attractive place for early settlement and agriculture, and the presence of an organised field system alongside the cairn hints at a landscape that was already well-managed by the time those fields took their current shape.