When the turf was stripped back, it revealed a surface covered in cupmarks, the small circular hollows pecked into rock that represent some of the oldest deliberate markings made by people in Ireland. The panel at Letter carries possibly twenty or more of these, along with accompanying grooves, all inscribed into an earthfast panel, meaning a slab set into the ground and immovable, its flat level surface apparently chosen with some care by whoever made it.

Cupmark art of this kind is generally associated with the Neolithic and Bronze Age periods, though it remains one of prehistory's more opaque puzzles. Unlike megalithic art, which decorates tombs and monuments with relatively legible spirals or lozenges, simple cupmarks offer little in the way of obvious meaning. They appear across Ireland, Britain, and much of Atlantic Europe, sometimes alone, sometimes in dense clusters, occasionally paired with grooves or channels as seen here. The Kerry example came to light recently, identified and described by Aoibheann Lambe following the deturfing of the panel, a process that has revealed prehistoric surfaces elsewhere in the country as peat cutting and land management continue to expose what lay beneath. The site was recorded in October 2022.

The panel sits earthfast, level with or just proud of the surrounding ground, which means it can be easy to overlook even once you know to look. The cupmarks themselves are shallow depressions, and the quality of light matters considerably when trying to read a surface like this; low raking light, particularly in the early morning or late afternoon, tends to pick out the marks far more clearly than midday sun, which flattens the texture of stone.