The site at Carrownacon is a rath, the Irish term for a ringfort, which was the standard form of enclosed farmstead across early medieval Ireland, typically housing a single family and their livestock. What distinguishes this one from a simple circular earthwork is that it is bivallate, meaning it has not one but two concentric earthen banks, with a fosse, or ditch, between them. That intervening fosse still reads clearly, dropping around 2.1 metres, and the tree-lined banks give the whole enclosure a quietly deliberate character that passive grazing land rarely holds onto.

The site was recorded as part of D. Lavelle's archaeological survey of the Ballinrobe district, published in 1994 by the Lough Mask and Lough Carra Tourist Development Association. At roughly 59 metres north to south and 52 metres east to west, it is a reasonably substantial example of the type. The inner bank, still standing around a metre high, retains gaps on the north-north-east, west, and west-south-west, which may echo original entrance points, though the western side has been partly overlain by a more recent field fence. The outer bank has fared less well, having been levelled between the south-west and north-west arcs. The interior sits slightly raised above the surrounding ground and slopes gently downward toward the banks on all sides, a topographic detail that suggests a long-settled and shaped landscape beneath the present pasture. Farm animals have disturbed the interior considerably, which is common for ringforts still in active agricultural use.