It measures roughly four metres north to south and three metres east to west, rising no more than sixty centimetres at its highest point, with a noticeably flat top. That flatness is the detail that catches the eye; natural ground rarely settles quite so deliberately.

The mound sits on a gentle rise, with the ground falling away to the south towards the Moy estuary and longer views east and north-east towards Enniscrone and Killala Bay. The shore is close on two sides, within fifty to seventy metres. To the north-east, marram-covered dunes edge the landscape. Around 350 metres to the west, a second feature, recorded as a mound barrow, is visible across the pasture. A barrow is a burial mound, typically prehistoric in origin, raised over a grave or series of graves, and the presence of two such features on a relatively small island suggests this corner of Mayo held some significance to the communities who once used it. Whether this particular mound shares that funerary character or served some other purpose has not been established from what survives above ground.

Bartragh Island sits in the mouth of the River Moy in Killala Bay, a stretch of water with a long history of settlement and movement along the north Mayo coast. The island itself is low-lying and largely uninhabited, accessible only by water or at low tide, which partly explains why features like this one remain in reasonable condition, undisturbed by the kind of agricultural activity that has levelled so many comparable earthworks on the mainland. The flat top and oblong profile are the clearest physical details to look for, modest as they are against the surrounding grass.