Its upper surface, roughly a metre square, is covered in prehistoric carvings that have been slowly losing definition to the Kerry weather for several thousand years. The motifs are extremely weathered now, but enough survives to make clear that whoever worked this stone was doing something considered and deliberate, composing a dense grammar of marks across a surface no larger than a kitchen table.

The carvings belong to a tradition known as cup-and-ring art, one of the most widespread yet least understood forms of prehistoric mark-making in Atlantic Europe, produced roughly between 4000 and 1500 BC. The technique involves pecking a small circular depression, the cup, into the rock surface, then surrounding it with one or more concentric rings, sometimes with a groove radiating outward from the cup like a spoke. At Coumreagh the vocabulary is unusually varied. There is a cup-and-three-rings motif along the western edge of the decorated surface, alongside cup-and-two-ring and cup-and-ring examples of differing sizes and proportions. One of the ring motifs is distinctly egg-shaped in plan rather than circular. A large oval area occupies the eastern side of the surface and trails off in a meandering line toward the south-east. Elsewhere, radial grooves extend from cups and terminate in further cupmarks, and short perpendicular returns branch off at angles. Sixteen individual cupmarks are scattered across the surface. The whole composition reads less like a geometric pattern and more like a series of decisions made over time, each motif placed in relation to what was already there. The site is documented in the 1996 archaeological survey of the Iveragh Peninsula by A. O'Sullivan and J. Sheehan, which remains the foundational catalogue of prehistoric remains in this part of Kerry.

The boulder sits in open mountain heath, with a small stream running about eight metres to the north and a low stone wall roughly twenty metres to the east. The view west along the Caragh river and north-west down the Bridia valley is long and uninterrupted. Whether the sightlines mattered to the people who carved the stone is unknown, but the position is conspicuous for a valley that otherwise keeps its archaeology quietly out of sight.