It is not the grand high cross of popular imagination, carved with gospel scenes and interlace knotwork. Instead it is squat, thin, and plain, with two stumpy arms angled slightly upwards and nothing on its surface except a smooth finish on the east face. It sits on a low cairn, a modest mound of stones that raises it just enough to mark its presence, and a whitethorn bush grows beside it, the kind of association between thorns and sacred sites that recurs throughout the Irish countryside.

The cross is thought to be of early Christian date, placing it roughly within the period from the fifth to the twelfth century, when Irish monasticism was producing some of its most distinctive stonework. What makes it archaeologically interesting is its shape. Simple cruciform crosses of broadly similar form appear on St MacDara's Island, off the south Connemara coast, and on Inchagoill, an island in Lough Corrib with its own early monastic remains. That cluster of comparisons suggests a regional tradition of plain, unelaborated stone crosses, functional markers of sacred space rather than vehicles for display. The Lackmacmahon example is believed to be in its original position, which gives it a quality that more travelled or relocated monuments lack. It has, as far as can be determined, always stood here, in this pasture, beside this road junction.