It is easy to overlook. The rock itself is fractured and naturally striated, less than half a metre at its highest point. But one face of it, a sub-rectangular surface roughly sixty by fifty centimetres and oriented to the east, carries marks that were put there deliberately, by a person with a tool, at some point in prehistory.

Cup-and-ring marks are among the most widespread and least understood forms of prehistoric rock art found across Atlantic Europe and beyond. They consist, as the name suggests, of a small circular depression, the cupmark, surrounded by one or more incised rings, and despite their frequency they have resisted any settled interpretation. The Derreeny example carries three of these motifs along the southwest margin of the decorated surface, each roughly nine centimetres in diameter with a cupmark of about two and a half centimetres across. Two of them, to the southeast, are clearly picked into the stone and remain sharply visible. The third, to the northwest, is defined by numerous individual pickmarks and is described as very distinct. Separate from these, a cluster of four plain cupmarks, slightly larger at three and a half to four centimetres across, sits to the northwest of the decorated area. The markings are well-defined overall, which is not always the case with outdoor rock art that has been exposed to centuries of weathering. Roughly eighteen metres to the south-southwest, a roofless ruin stands in the same rough pasture, its own history unrecorded, its proximity to the carved rock unexplained.