What sets it apart is not its geology but its more recent history: local tradition holds that this stone, roughly diamond-shaped and measuring about three and a half metres along its longest axis, served as a mass rock during the Penal Era. Mass rocks are the outdoor altars, often natural flat-topped stones, where Catholic priests celebrated Mass in secret after the Penal Laws of the late seventeenth and eighteenth centuries banned Catholic worship and stripped priests of any legal standing. The stone here has a slightly convex, irregular top surface of roughly a metre by a metre and a half, wide enough to serve as a makeshift altar and flat enough to hold vessels. The valley it sits in is hidden from the surrounding lowland, yet from within it the ground opens up to wide views north-west to north-east, across Lough Conn and over Foxford and its fields below.

The concealment was deliberate and carefully managed. About 300 metres to the north-east of the mass rock stands a rocky bluff known locally as Braid, marked as Carranarah on the 1930 Ordnance Survey six-inch map. Defined on three sides by cliffs, it commands clear sight lines over Foxford village and over the routes leading up toward the valley. Tradition recorded by Tommy Doherty of Foxford holds that Braid functioned as a lookout post while Mass was being celebrated below. Sentinels watching from the bluff would signal approaching danger using whistles made from hollowed-out cabbage stalks, giving the priest enough warning to slip away before soldiers or informers reached the site. It is a detail that carries the texture of lived necessity rather than later embellishment: improvised, practical, and entirely dependent on the landscape working in the congregation's favour.