A semi-circular cropmark, roughly 32 metres in diameter, appears in aerial imagery taken between 2011 and 2013, its outline defined by a ditch with a gap or open area facing south-west. Cropmarks form when buried features such as ditches or walls affect how vegetation grows above them, typically showing up as subtle differences in colour or density during dry spells. What makes this particular mark arresting is its setting: Lough Derravaragh is the lake most associated with the legend of the Children of Lir, and its shoreline has clearly held human attention for a very long time.

The earthwork also appears on the Ordnance Survey Ireland 25-inch map series, one of the most detailed historical map surveys carried out in Ireland, where it is recorded as a raised circular area defined by a scarp, a term referring to a steep slope or edge in the ground surface. The two sources, the older cartographic record and the more recent aerial imagery, do not describe exactly the same form, which is itself telling. The map suggests a physical upstanding feature; the cropmark points to something now largely levelled and buried. Together they indicate an enclosure of some antiquity, though without excavation it is not possible to say with certainty what purpose it served. Circular or semi-circular ditched enclosures in Ireland range from prehistoric ring-ditches associated with burial to early medieval enclosed settlements, and the evidence here does not yet allow a narrower interpretation.