It is not much to look at from a distance, measuring roughly one and a half metres by just over a metre. But its surface carries a quiet puzzle: a scattering of cupmarks, those small circular depressions pecked into stone by prehistoric hands, arranged in clusters and enclosed by rings and part-rings, with one motif framed by a triangular groove with rounded corners, a form unusual enough to catch the eye of anyone who knows what they are looking for.

Cupmark art of this kind is generally associated with the Bronze Age, though its precise meaning and function remain unresolved. The Derreeny examples are poorly preserved; lichen and black moss obscure some motifs, and further decoration may lie hidden beneath the encroaching peat. What survives on the western side of the decorated surface includes a triple cupmark enclosed by a single ring, a possible cup-and-ring motif with a very faint outer circle, and a semi-circular ring beside another cupmark. The eastern side holds its own sequence: four cupmarks in loose arrangement, one of them oval in shape and enclosed by that distinctive triangular ring. A picked square area sits close by, its purpose unknown. The rock lies flat and exposed to the elements on a south-facing slope at around 163 metres above sea level, overlooking the valley of the Kealduff River. Roughly 35 metres to the east, the remains of a deserted clachan, a small cluster of rural dwellings, mark another layer of occupation on the same hillside. Two further rock art sites lie approximately 16 metres to the west, suggesting this stretch of Knockaunanattin was a focus of some significance, though precisely when, and why, nobody can say with confidence.