It measured roughly 64 metres across, a univallate enclosure, meaning it was defined by a single bank and ditch, and it was substantial enough to be mapped twice: first on the Ordnance Survey's original six-inch edition of 1839, and again on the 1900 revision. By the latter half of the twentieth century it was still physically present, visible as an upstanding earthwork in aerial photographs taken in 1966 and 1970. Sometime after that, it was levelled, most likely through continued agricultural activity. It survives now only in maps and photographs.

What makes Garnagale quietly remarkable is what one of those aerial photographs revealed beneath the later enclosure. The 1970 image shows the double arc of an older, bivallate enclosure, one with two concentric banks and ditches rather than one, curving beneath the south-western quadrant of the structure that replaced it. The two monuments occupy the same ground across an unknown span of centuries, the earlier form partially absorbed or buried by the later one. Enclosures of this kind are broadly associated with early medieval settlement in Ireland, where a ringfort or enclosed farmstead formed the basic unit of rural life, though the precise date and function of either monument at Garnagale has not been established from the available information. The fact that the site was still legible in aerial photography as recently as 1970, and that the palimpsest of the earlier enclosure was only visible from the air, speaks to how much of the Irish landscape carries buried or erased layers of occupation that ground-level observation simply cannot reach.