The earthen bank that survives runs from south, around through west, to north, enclosing what would once have been a roughly circular space of around forty metres in diameter. The eastern quadrant is simply gone, levelled at some point between the mid-nineteenth and early twentieth centuries, leaving the monument as a kind of interrupted parenthesis in the landscape.

A ringfort, or rath, is an enclosed homestead of the early medieval period, typically defined by one or more circular earthen banks and ditches. They were the ordinary dwelling places of farming families across Ireland, numbering in the tens of thousands, and their survival rate today varies enormously depending on what the land was subsequently put to. The Garryroan example appears on the first edition Ordnance Survey six-inch map of 1843 as a complete enclosure; by the 1906 edition, the eastern portion had already disappeared. The surviving bank is a modest but legible feature: the crest is around 2.2 metres wide, the base spreads to 6.4 metres, and the bank rises just over a metre above the interior ground surface. These are unspectacular dimensions, but they are consistent with a typical single-banked rath. The woodland of whitethorn, blackthorn and conifers that now covers the site has preserved what remains while also making it harder to read as a coherent shape from the ground. In the north-east, there is evidence of small-scale quarrying, along with what appears to be upcast material associated with it, which may partly explain the loss of the eastern quadrant.