On the surface it presents as little more than a low scarp, a slight drop in the land that traces a rough circle roughly forty metres across. What makes it more interesting is what lies beyond that visible edge: faint cropmarks, detectable in aerial imagery, suggesting two concentric fosses, or ditches, curving around the site to the north-west and north-east. A foss of this kind would originally have been dug as a boundary or defensive feature, and the presence of two of them, running concentrically outside the main enclosure, hints at something more elaborately arranged than the scarp alone would suggest.

The site came to wider attention through aerial observation rather than ground survey, reported by Jean-Charles Caillere and confirmed through Google Earth imagery captured in March 2011. Cropmarks of the kind visible here form when buried features such as filled ditches affect the growth of grass or grain above them, producing subtle differences in colour or height that are invisible at ground level but readable from above, particularly in dry summers when soil moisture varies. The enclosure sits in an agricultural landscape that already contains at least one other early medieval monument: a ringfort lies approximately seventy-five metres to the south-west. A ringfort is a roughly circular enclosed settlement, typically dating from the early medieval period, defined by one or more earthen banks and ditches. Whether the enclosure at Knockadangan is related to that ringfort in date or function remains an open question, one that the ground itself has not yet been asked to answer.