No earthwork rises from the field, no stone protrudes, no hollow marks the ground. The only evidence for this possible enclosure is a cropmark, a ghostly outline that appeared on an aerial photograph and nowhere else.

Cropmarks form when buried features, such as ditches, walls, or pits, affect the growth of crops or grass above them. Buried ditches retain moisture and nutrients, producing lusher, taller vegetation; buried walls or compacted surfaces do the opposite. From the air, under the right conditions of drought and low-angled light, these differences become legible as faint rings, lines, or shapes that would be entirely invisible to someone walking the same ground. The aerial photograph on which Ballynakill's possible enclosure was identified carries the reference GSI N 454/455, placing it within the archive of the Geological Survey of Ireland. What the photograph shows is consistent with an enclosure, a category of monument common across Ireland and typically associated with settlement, agriculture, or ritual activity from the prehistoric through to the early medieval period, though in this case the evidence is too limited to assign a date or a function with any confidence.