The mound is roughly 9.6 metres long and 7.9 metres wide, and its most distinctive feature is a horseshoe-shaped depression at its core, a form that appears in thousands of similar monuments across Ireland and is closely associated with ancient cooking or processing activity. Burnt material has even worked its way into the field fence bordering the site to the south and southeast, suggesting the mound has been disturbed or spread over time by agriculture.

This is a fulacht fia, a type of monument found widely across the Irish landscape, typically dating to the Bronze Age. The term refers to a mound of fire-cracked stone and charcoal-stained earth that accumulates beside a trough, usually timber-lined, into which water was poured and heated by dropping in stones fired in an adjacent hearth. The horseshoe or crescent shape so characteristic of these sites is the debris ring that builds up around the working trough as spent, shattered stones are discarded. The Ballyduff example was recorded in 1986 as part of the Castleisland District Archaeological Survey. The horseshoe portion of the mound measures 6.7 metres in length and 4.5 metres in width, with the most pronounced internal and external slopes running through the eastern and southeastern arc of the monument. A concentration of rush growth in the southern portion of the mound points to persistent waterlogging, which is entirely in keeping with a site type that depended on a reliable source of water.