They are small enough to cover with a fingertip, each roughly seven or eight millimetres across and two millimetres deep, yet they are described as perfectly formed and identical, clustered together in the northwest corner of the stone's decorated face. The overall decorated area measures only ten centimetres by ten centimetres. The scale is almost domestic, which makes the precision feel stranger rather than less impressive.

The boulder itself sits at around 94 metres above sea level on a gentle northeast-facing slope, with the Kealduff River running some ten metres to the northeast. The stone is fractured sandstone, roughly a metre north to south and 1.3 metres east to west, and its carved face looks westward. Rock art of this kind, typically produced by pecking or picking into stone surfaces during the Neolithic or Bronze Age, is found across Ireland, usually taking the form of cup marks, rings, or more complex abstract motifs. What is unusual at Derrynablaha is the suggestion that these particular marks may not be purely abstract at all. The landscape around the boulder is scattered with large glacial erratics, boulders deposited by retreating ice sheets during the last glaciation, and the arrangement of the pickmarks may correspond to the positions of those erratics in the surrounding terrain. If that interpretation holds, then the decorated surface becomes something closer to a map, an early attempt to record the physical world in miniature on stone.