It does not appear on Ordnance Survey maps. Thorn bushes have claimed much of its interior and swallowed the northern arc of its banks almost entirely. And yet, from the air, the structure is unmistakable: a roughly subcircular form, approximately 70 metres north to south and 65 metres east to west, defined by two concentric banks of earth and stone with a broad, flat corridor between them stretching some 13 metres in width.

Concentric enclosures of this type are among the less understood features of the Irish landscape. They consist of multiple roughly circular earthen or stone boundaries, one inside another, sometimes interpreted as high-status settlement enclosures, ceremonial spaces, or the remains of early medieval ringforts with elaborate outer defences. At An Carn Mór Thiar, the inner bank survives to a modest height, visible from the east-northeast around to the southwest, while the outer bank has spread into a low, grass-covered scatter of boulders along a similar arc. Notably, there is no fosse, the defensive ditch that typically accompanies a ringfort, which sets this structure somewhat apart from that category. A possible causewayed entrance, around 1.9 metres wide and flanked by two low boulder banks, appears on the eastern side. To the south, traces of a field wall extend outward from the outer bank, suggesting the enclosure may have sat within a broader field system. A second enclosure lies roughly 85 metres to the southwest. The site was previously noted by Sutton in 2009, though it remains absent from standard mapping.

The monument sits in ordinary farmland, cut through by later field walls that slice across both banks at the west-northwest and east-northeast. A possible hollow or pit, its purpose unclear, lies overgrown in the western sector of the interior. The whole is so thoroughly colonised by scrub that much of its structure must be inferred rather than walked. The M6 runs immediately to the south, close enough that the contrast between the ancient earthwork and the motorway infrastructure pressing against it is difficult to ignore.