The earthwork was recorded as a circular enclosure on the first edition Ordnance Survey six-inch map of 1839, and by the time of the revised survey it had already declined to a circular depression with trees growing inside it. At some point after that it was levelled entirely, leaving nothing visible to a person standing in the field. And yet the monument refuses to disappear completely.

A henge is a class of ceremonial enclosure associated with the Neolithic and Early Bronze Age, typically defined by a bank placed outside a ditch rather than inside it, which suggests the boundary was symbolic rather than defensive. The Clashwilliam example fits that pattern well. According to aerial photographs taken in the summers of 1968, 1969, and 1971, the site shows up as a well-defined cropmark, the kind of ghost image that forms in dry conditions when buried features cause overlying crops to ripen or stress at different rates. The enclosure measures approximately fifty metres in diameter and is defined by a wide, deep inner fosse, a broad outer bank, and what appears to be a further slot trench encircling the whole arrangement. A possible single entrance faces east, an orientation that recurs at a number of prehistoric ceremonial sites elsewhere in Ireland and Britain. The structural complexity noted by Gibbons in 1990, with its layered sequence of ditch, bank, and outer trench, points to a monument of some elaboration rather than a simple enclosure.

There is nothing for a visitor to see at ground level today. The site survives only in archive photographs and on old maps, its geometry preserved in the rhythm of a crop on a summer afternoon, visible from the air but not from the lane.