In dry summers, the buried ditches and banks of an ancient circular enclosure alter the moisture available to roots above them, producing faint colour and height differences in the crop that, seen from the air, resolve into a clear geometric pattern. This kind of aerial evidence, known as a cropmark, is frequently the only trace left of earthworks that have been levelled by centuries of ploughing.

What the cropmark reveals at Ballyarra is a bivallate enclosure, meaning it was originally defined by two concentric banks and their accompanying ditches, or fosses. The overall diameter runs to roughly thirty metres, which places it in the range of a small ringfort, the type of enclosed farmstead that was the dominant form of rural settlement in early medieval Ireland. Three fosses are visible in the cropmark, narrowing progressively from the innermost to the outermost, which suggests the defences were carefully graded rather than uniform. The entrance faces north-east, and the outer two fosses curve slightly inward at that point, a feature that would have created a more controlled and perhaps more defensible approach. Just to the north-east, in an adjacent field, further linear cropmark features hint at associated activity, possibly field boundaries or enclosures connected to whatever settlement once occupied this ground.