A low rise running from south to west is the clearest physical trace left of what was once an oval earthwork enclosure, roughly thirty metres across east to west and twenty metres north to south. The rest has been absorbed into the surrounding pasture, its banks levelled so gradually and thoroughly that the site is easier to understand on a nineteenth-century map than on the ground itself.

Ringforts, known in Irish as raths, were enclosed farmsteads, typically circular or oval in plan and defined by one or more earthen banks, used throughout the early medieval period in Ireland. The Mashanaglass example first appears clearly on the Ordnance Survey six-inch map of 1842, drawn as a hachured oval set within a small rectangular field, with a bank running east to west forming the southern corner of that field. By the time the 1904 and 1938 OS maps were produced, only the northern quadrant was still being marked with hachures. When P. J. Hartnett visited and recorded the site in 1939, he found that quadrant physically cut off from the rest of the enclosure by two earth and stone field fences running north-west and north-east, with what he described as vague traces of the rampart still visible outside those fences, particularly along the south-western quadrant. The field boundaries, in other words, had been built directly through the body of the fort, and the remainder had been cleared away around them.