Cairns, in this context, are mounds of heaped stone raised over burials or as territorial markers during the Bronze Age or earlier, and the examples on Knockroe have not fared especially well across the centuries. Relay stations occupy the hilltop, and their construction has denuded and partly damaged all three monuments, leaving them considerably reduced from whatever scale they once commanded.

The largest of the three cairns sits at the highest point of the hill, at an elevation of 554 feet above sea level. It is circular in plan and measures about 12 metres in diameter, though its profile is now very low. At some point it was pressed into service as a trigonometrical station, one of the fixed reference points used by surveyors to map the country with precision. A second cairn lies roughly 12 metres to the south, also circular, measuring 9 metres across and surviving to a height of about 1.6 metres, which makes it the best-preserved of the group despite the concrete trigonometrical marker now planted on top of it. A third, smaller cairn sits approximately 14 metres to the north-east of the first, only 5 metres in diameter and barely half a metre high. Together the three form a close cluster on the one prominent summit, which raises the possibility that Knockroe held some significance in the prehistoric landscape of this part of north Galway, perhaps as a place deliberately chosen for the accumulation of monuments over time, though the damage they have sustained makes any detailed interpretation difficult.