Ordnance Survey cartographers recording the landscape in 1838 marked it as a circular enclosure roughly twenty metres across and labelled it, simply, "McMahon's Monument", attaching a relatively recent local surname to a structure whose origins reached back to the Bronze Age or earlier. By 1929, the same feature had been reclassified on updated maps as a "Dolmen", a term then commonly applied to megalithic structures, though the monument was in fact a wedge tomb, a type of prehistoric burial chamber characterised by a gallery that narrows and lowers toward one end, typically oriented toward the setting sun.

The name McMahon's Monument hints at something that happened repeatedly across Ireland: ancient structures absorbed into local memory and re-christened after families or individuals whose connection to them is now lost. Whether the McMahon in question was a landowner, a local notable, or simply someone associated with the field in which the stones stood, no record appears to have survived. What is documented is the monument's fate. During land reclamation works in the early 1950s, the structure was destroyed, its stones cleared away to make agricultural ground more workable. Ruaidhrí de Valera and Seán Ó Nualláin recorded what was known of it in their Survey of the Megalithic Tombs of Ireland, Volume II, covering County Mayo, published in 1964, by which point the monument had already been gone for a decade.