There is nothing to see at ground level: no earthwork, no raised bank, no visible trace of any structure. The enclosure exists, for all practical purposes, only from the air, and even then only under the right conditions. It has never appeared on Ordnance Survey historic mapping, which means it slipped entirely through the cartographic record that documents so many other Irish sites.

The site came to light in the early 1990s when Celie O'Rahilly, an archaeologist working with Limerick County Council, noticed something unusual while examining aerial photography taken by the Ordnance Survey of Ireland in 1985 (reference OS 3/9134). What she identified was a cropmark, the faint but legible ghost of a buried feature that influences how grass or crops grow above it. Buried ditches tend to retain more moisture, producing slightly lusher growth, while buried walls or compacted surfaces do the opposite. The result, visible only in dry summers or at particular angles of light, is a pattern in the vegetation that mirrors what lies beneath. The Clonmacken cropmark is circular in form, and the same shape has since been confirmed on Digital Globe aerial orthoimagery taken between 2011 and 2013, and again on a Google Earth image dated 18 March 2015. The photography was originally examined as part of preparations for the Limerick South Ring Road. The site sits on low-lying, poorly drained pasture roughly 120 metres north of the Shannon.

Because there is nothing visible at the surface, and because the site is on private agricultural land, there is no conventional way to visit it in any meaningful sense. The most useful approach is through the aerial imagery itself: the Google Earth record from March 2015 gives a reasonably clear impression of the cropmark's circular form. The surrounding landscape is flat and unassuming, which makes the abstract geometry of the mark all the more striking when seen from above. The site was compiled in the national record by Alison McQueen, Vera Rahilly, and Caimin O'Brien, and uploaded in June 2020.