Mostly buried in the ground, with its western and southern sides only partially exposed, the stone measures roughly 1.8 metres north to south and 1.2 metres east to west. Across its surface are scattered 21 cup marks, the shallow circular depressions, typically between four and seven centimetres in diameter and two to three centimetres deep, that are the defining feature of prehistoric rock art across Ireland and Britain. Two further, smaller indentations may also be present, though whether these are genuinely ancient or simply the result of later weathering and damage is uncertain.

What makes Carrigeenduff quietly anomalous among Irish rock art sites is the addition of something more deliberate and geometric. At the northern end of the boulder, a small square area, roughly twenty centimetres on each side, has been outlined and contains an incised X. Cup marks of the kind found here are generally attributed to the Neolithic or Bronze Age, produced by unknown hands for purposes that remain a matter of debate, whether ritual, territorial, astronomical, or otherwise. The squared frame and its X, however, sit apart from that tradition; whether they belong to the same period of activity or represent a later intervention by a different hand, in a different era and with a different intention, is not recorded.