The decorated surface, roughly fifty centimetres by thirty-two, faces south-east and holds a cup-and-ring motif, a form of prehistoric carving in which a shallow central hollow, the cup, is surrounded by one or more incised concentric rings. Here there are three rings, and the composition does not stop there. Three separate grooves extend outward from the design, two from the outermost ring and one from the cupmark itself, all eventually meeting or joining a longer groove that runs perpendicular to the south and ends in a short return at its eastern end. The cupmark is notably deep, possibly deepened further by centuries of natural erosion rather than by the original carver's hand alone.

Cup-and-ring art of this kind is generally associated with the Neolithic and Bronze Age periods, roughly between five thousand and three thousand years ago, though its precise meaning and purpose remain matters of genuine scholarly debate. The Iveragh Peninsula, on which Kealduff sits, was documented extensively by archaeologists Annngret O'Sullivan and John Sheehan in their 1996 survey of South Kerry, published by Cork University Press, and this boulder appears as entry number 334 in that catalogue. The decorated surface of the sandstone rock sits at 148 metres above sea level on an east-facing slope, with the River Behy valley visible to the east, though field boundaries to the north and north-east interrupt what would otherwise be a wide prospect. Two ancient trackways pass close by, one about six metres to the west running north-west to south-east, another immediately to the south running roughly east to west, suggesting this spot sat within, or perhaps beside, a landscape that was regularly crossed and used.