Spread across a west-facing slope of rough grassland, the rath here is so degraded that for most of recorded history it simply went unnoticed. It only came to light in September 1984, when aerial reconnaissance picked out its outline from above, a reminder that Ireland's landscape still holds features entirely invisible at ground level.

A rath is an early medieval enclosure, typically circular or subcircular in plan, formed by earthen banks and ditches and associated with farmsteads of the early Christian period. The Masmore example measures approximately 77 metres east to west, which places it at a substantial size, yet almost nothing of it reads clearly on the surface. What survives is a degraded scarp, an intervening fosse (a ditch running between the inner and outer elements), and an outer bank, all of it detectable only along the arc running from the north-east through the south to the north-west. Beyond that arc, no visible surface trace remains. A number of later field walls radiate outward from the monument, suggesting that at some point the old earthwork became a convenient anchor point for agricultural boundaries, its original function long forgotten by whoever was laying out those divisions.

That combination, a site of considerable scale rendered almost legible only from the air, and then overlaid with the pragmatic geometry of later farming, is quietly characteristic of how early medieval settlement has survived, or failed to survive, in the west of Ireland.