The walls push up through the surface intermittently, tracing a roughly triangular area around 240 metres across at its eastern edge and extending some 300 metres to the west. They are not tall, reaching perhaps 0.4 metres above ground, and not thick, around 0.6 metres across, but they are made of substantial boulder-type stones and occasional slabs, laid out in curvilinear lines that curve and shift in direction rather than running in the straight geometries of later field systems. Stretches of them are buried under deeper bog or swallowed by gorse and moor-grass, so that what a walker encounters is something fragmentary and suggestive rather than a clear, readable landscape.

These are what archaeologists call relict field walls, the surviving traces of an agricultural system that predates the bog which now covers them. In many parts of Ireland, particularly in the west, blanket bog has preserved and then partially re-exposed ancient field boundaries of this kind, sometimes dating to the Bronze Age or earlier, when the climate was warmer and the uplands supported cultivation or managed grazing. The walls at Com Na Heorna Thoir, recorded by O'Sullivan and Sheehan in 1996, sit on rough hill grazing ground that is uneven and difficult underfoot, the kind of terrain that tends to discourage casual exploration and allows such features to persist largely unnoticed. The place-name itself, referring to the eastern end of a valley associated with barley, suggests that this ground was once considered worth naming in agricultural terms, which sits quietly alongside the physical evidence of the walls themselves.