It rises only about sixty centimetres above the surrounding ground, easy to miss beneath the leaf litter, yet it represents a type of site found in extraordinary numbers across Ireland. This is a fulacht fia, a kind of prehistoric cooking or processing site typically consisting of a trough dug near a water source and a mound of fire-cracked stone accumulated over repeated use. The stones were heated in a fire, dropped into a water-filled trough to bring it to the boil, and discarded once spent; over time those discarded stones built up into the characteristic mound that survives today.

The Mashanaglass example follows the form closely. Its opening faces east, towards the stream on whose bank it sits, and the accumulated burnt material forms the familiar horseshoe shape around what would once have been the working area. The northern arm of the mound has been cut through at some point, disturbing the profile on that side, and a stone protrudes from the tip of the northern arm, possibly the remnant of some structural element or simply an exposed boulder incorporated into the spread of material. Fulachtaí fia are most commonly associated with the Bronze Age, though some sites have produced evidence of use across a wider span of time. The proximity to running water is typical; a reliable, replenishable water source was essential to the whole process.