Its near-circular form measures roughly 35.7 metres east to west and 34 metres north to south, and it retains two earthen banks separated by a fosse, the term used for the ditch dug between defensive or enclosing earthworks. The outer bank survives most clearly from the west-northwest around to the east, and a possible original entrance can be traced at the southeast.

Ringforts, known in Irish as raths when constructed from earthen banks rather than stone, are among the most common archaeological monuments in the Irish landscape, with tens of thousands recorded across the island. Most date from the early medieval period, roughly the fifth to the twelfth centuries, and typically enclosed a farmstead or the dwelling of a local family of some standing. A double-banked example like this one at Sonnagh would generally have belonged to a household of higher social rank than those enclosed by a single bank. The site was noted by Knight around 1975 and by Conway around 1980, both of whom recorded its condition and form before it entered the broader archaeological record for North Galway.