With a diameter of roughly 90 metres, this large feature exists, at least for now, almost entirely as a cropmark, a faint discolouration in the soil and vegetation that becomes legible only when viewed from above under the right conditions. It was first identified in 1973 on an aerial photograph, and it has not become any easier to see since. Stand in the field today and there is nothing to report.

Cropmarks form when buried features, ditches, walls, or pits, influence how crops or grass grow above them. Filled-in ditches tend to retain moisture and nutrients, producing lusher, taller growth that registers as a darker stripe or curve from altitude. At Ballynamurragh, the broad sweep of that buried curve suggests something substantial once stood or was enclosed here, though no excavation has confirmed its date or purpose. What complicates matters further is a note recorded from local sources: there was once a vegetable garden somewhere in this area. The field has since been drained, removing the marshy, waterlogged conditions that might have helped preserve organic traces underground. Sitting only about ten metres to the south-west is a ringfort, a type of enclosed farmstead common across early medieval Ireland, typically consisting of an earthen bank and ditch surrounding a domestic settlement. Whether the two features are related, contemporary, or entirely coincidental remains an open question.