The earthwork at Garrynalyna appears in satellite imagery as a large oval cropmark, the kind of ghost-outline that emerges when buried or disturbed soil causes crops or grass to grow differently above an ancient feature. It takes a certain angle, and a certain altitude, to see it at all.

The site was first recorded cartographically on the Ordnance Survey Ireland six-inch map of 1840, where it was shown as a raised, sub-circular platform defined by a scarp, essentially a low bank or slope marking the edge of what may once have been an enclosure. Enclosures of this kind are among the most common monument types in the Irish landscape, often associated with early medieval settlement, though their dates and functions vary considerably. What is notable here is that after that first appearance in 1840, the feature disappeared from all subsequent editions of the historic OSi maps, suggesting the earthwork had either been largely levelled or simply went unrecorded in later surveys. It resurfaced, in a sense, in aerial photographs taken on 3 November 1984 during work on the Bórd Gáis Éireann Curraleigh to West Limerick gas pipeline, where it showed as a sub-circular cropmark. Decades later, it appeared again as a large oval cropmark on Digital Globe orthoimagery captured between 2011 and 2013, and once more on a Google Earth image dated 18 November 2018. A related possible enclosure has been recorded roughly 45 metres to the south.

The site sits in pasture approximately 165 metres east of the townland boundary with Knockaunacurragha, which gives some orientation if you are working from a map, though there is nothing visible on the ground that would draw the eye. The feature is essentially an aerial monument, one whose presence registers only through the subtle chemistry of soil and vegetation rather than any surviving physical structure. Visiting in a dry summer, when cropmarks are at their most pronounced, would give the best conditions for any aerial observation, though most people encounter this one through the orthoimages compiled in the national record.