The monuments sit in a close-set north-west to south-east line along the ridge top, and the one at the north-western end occupies the very tip of the ridge, spanning its full width as though it were placed there to mark the point precisely. The ground drops away to the south-south-west toward the Trimoge River, which meanders below and bends just to the north-west of the site. Views from the ridge are not wide-ranging for the most part, but a gap in the surrounding hills opens a long sightline to the north-west, where Nephin Mountain and the Nephin Beg Range come into focus.

A ring barrow is a burial monument of prehistoric origin, typically consisting of a raised central platform ringed by a ditch, known as a fosse, and an outer bank. The example at Collagh follows this pattern closely. The central circular platform measures 4.7 metres in diameter and is defined by a low scarp with a faint internal lip. Around it runs a fosse between 1.5 and 1.7 metres wide, and beyond that an external bank roughly 1.7 metres wide and between 0.2 and 0.4 metres high. A causeway-like feature, 1.5 metres wide, crosses the fosse at the south-west, suggesting a deliberate point of access to the central platform. The whole structure is now covered in heather and sits within pasture. What makes the chronological picture murkier is that the monument does not appear on Ordnance Survey six-inch maps from either 1838 or 1931, meaning it escaped cartographic notice for well over a century despite its prominent position on the ridge.