Yet the nearly flat face of this stone at Coomasaharn carries prehistoric rock art, a category of monument that remains genuinely puzzling to archaeologists: nobody knows with certainty who made it, or why. The decorated surface measures roughly 0.8 metres by 0.75 metres, modest enough to crouch over, and the marks cut into it are subtle even before weathering is taken into account.

The motifs belong to a tradition found widely across Atlantic Europe during the Neolithic and Bronze Age. Cups, meaning shallow circular depressions pecked into the rock, appear here in two forms. Three are simple cupmarks, each about 4 centimetres across and only 3 to 4 millimetres deep, clustered toward the northern part of the surface. The remaining seven are cup-and-ring motifs, where a central cupmark is surrounded by one incomplete concentric ring. The rings on this stone are all broken rather than fully closed, most likely because weathering has worn away the shallower edges over the millennia. At 1 centimetre wide and 2 to 3 millimetres deep, they were never deeply incised, and two of the motifs are now extremely faint. The stone itself is sandstone, smooth in places and fractured in others, sitting on a north-east-facing slope at around 186 metres above sea level, with open views across the Behy River valley toward Glenbeigh.

The surrounding landscape offers some context for the stone's setting. The rock sits in an area of cutaway bog, ground that has been worked for turf over generations, and a bog trackway runs roughly 2.2 metres to the south-east. The carved surface has a very slight north-north-east aspect, and though it would be easy to read meaning into that orientation, the incomplete rings and heavy weathering make it difficult to say much about the original arrangement of the motifs with any confidence. What is clear is that someone chose this particular outcrop, on this particular slope, and spent time working on it, leaving marks that have survived, just barely, into the present.