The evidence for it comes from a cropmark, the faint but readable difference in how crops grow over buried features, where ancient ditches or banks beneath the soil cause vegetation above them to ripen at a different rate or reach a different height than the surrounding field. From the air, under the right conditions, the outline becomes legible. What it reveals here is a bivallate circular enclosure, meaning one defined by two concentric rings of bank or ditch, roughly thirty metres in diameter.

Circular enclosures of this kind are widespread across Ireland, and while many are associated with the early medieval period, roughly the fifth to the twelfth centuries, they vary considerably in date and function. A bivallate example, with its doubled boundary, may indicate higher status, a need for greater security, or simply a different tradition of construction. Without excavation it is impossible to say more with confidence about Cooladurragh specifically. The site was recorded as part of a county-wide archaeological inventory published in 1994, and its presence is known only through aerial observation, with the cropmark pattern catalogued under the CASAP programme, a systematic effort to identify and document sites visible from the air across Irish farmland.