The decorated surface is modest, barely sixty centimetres by forty, and the motifs are small enough that a person could walk straight past them without registering anything unusual. That is, in fact, quite likely to happen, given that the outcrop sits at 149 metres above sea level, embedded in furze and molinia grass on a north-east-facing slope with a small stream running nearby.

The markings themselves belong to the tradition of prehistoric rock art found across Atlantic Europe, most densely in Ireland, Scotland, and Iberia, and generally dated to the Neolithic or Early Bronze Age. Cup-and-ring marks, the most recognisable form, consist of a shallow circular depression, the cupmark, surrounded by one or more incised concentric rings. At Kealduff, one such motif is present, with two rings encircling a cupmark roughly six centimetres in diameter, the whole composition measuring about 27 centimetres east to west. Two further plain cupmarks sit to the south of it, and a straight linear groove, 22 centimetres long, runs to the west. All three elements are clustered together at the northern end of the boulder, which is otherwise unfractured and roughly rectangular, rising to a maximum height of 1.4 metres. What the symbols meant to those who made them remains genuinely unknown. Interpretations range from territorial markers to astronomical records to ritual deposits, but none has won consensus, and the carvings offer nothing to resolve the question.

The boulder faces south-west across heath and outcrop, but the slope behind it opens north-east towards the River Behy valley, which is visible from the site. The surrounding vegetation, dense furze in particular, makes the approach rough rather than technical, and the decorated surface, with its south-west aspect on a subrectangular face of sandstone, is best viewed in raking light that throws the shallow incisions into relief. The carvings are only a few millimetres deep at most, and in flat or bright overhead light they can be almost impossible to read.