The rath at Mocollagan, in low-lying pasture in County Mayo, went considerably further. It was enclosed by three concentric earthen banks, with two deep fosses, or ditches, cut between them, giving the whole structure a total spread of roughly 83 metres north to south and 72 metres east to west, even though the central enclosure itself measures only around 45 metres in diameter. A triple-banked ringfort is a relatively rare form, generally associated with higher-status occupants, and this one sits in a landscape that already has two further ringforts visible to the north-east, suggesting a concentration of early settlement activity in this part of the Ballinrobe district.

The innermost bank stands about 1.1 metres high, the middle one reaches 1.5 metres, and the outer bank rises to around 1 metre, the outermost ring of a layered defensive arrangement that would have made any approach to the interior a slow and controlled affair. Beneath the interior, a souterrain was recorded, an underground stone-lined passage or chamber of the kind commonly associated with Irish ringforts, most likely used for storage or, in moments of danger, as a place of concealment. The site appears in a 1994 archaeological survey of the Ballinrobe area covering the wider districts of Lough Mask and Lough Carra, which catalogued it among a cluster of monuments in the surrounding townlands.

The banks are now heavily overgrown, and numerous gaps have opened in them over time, whether from agricultural activity or simple decay. That overgrowth can make the full scale of the earthworks difficult to read from ground level, but it also means the site retains a certain undisturbed quality, its three concentric ridges still legible beneath the vegetation for anyone willing to pace them out across the pasture.