For most of its length, the Claidh Dubh, which translates loosely as the Black Ditch, has been absorbed into ordinary field boundaries and townland fences, its original form overwritten by centuries of agricultural use and estate improvement. Only at certain points does it betray anything out of the ordinary, a bank a little too tall, a fosse a little too deliberate, a flat-topped ridge standing conspicuously clear of vegetation.

Excavations carried out at the southern end of the earthwork, in the valley of Gleann na nDibergach, revealed how substantial the original construction was. The bank reached 1.8 metres in height and nearly 4.75 metres in width, with V-shaped ditches on both its western and eastern sides, and what may have been a palisade trench along its eastern edge. Just beyond the eastern ditch lay a stone-paved trackway, 2.1 metres wide. Radiocarbon dating of peat overlying that trackway produced a date of 1801 plus or minus 39 years before present, placing it in the period roughly 139 to 250 AD, though the earthwork itself may be earlier still. Along the northern sections, field inspection has recorded a stone-faced double bank near Renny Upper, an unusually tall bank of over two metres near Scrarour, a flat-topped bank at Kilconnor that remains bare of vegetation, and a stretch near Skahanagh More where the feature follows the Fluckane stream, its bed flat and its sides stone-lined. Whether this last section represents a mill-race, as one researcher proposed, or can be identified with the Glaise Muilinn Mairteil, the stream of Martel's Mill mentioned in an early medieval text, is a question that has not been fully resolved. That text, a 15th-century manuscript known as Crichad an Chaoilli, appears to describe a boundary between two triuchas, which were territorial divisions of early medieval Ireland, and the line it traces corresponds closely to the course of the Claidh Dubh. The historian Kenneth Nicholls concluded that the earthwork does not match any territorial boundaries known from after 700 AD, suggesting its origins lie further back still, in a period before the record becomes clear.

The earthwork is known locally as a feature of remote antiquity, and its Irish name has persisted in oral tradition long after the physical form became difficult to read on the ground. Much of it is accessible only by following field boundaries and reading the landscape carefully, and certain sections remain ambiguous even to specialists who have walked the entire length.