The stone barely clears the bog at its tallest point, no more than 0.75 metres at the southeast wall, and most of the original masonry was carted away for use elsewhere long before anyone thought to record the site. It had apparently already fallen by 1865. Around the base, a thin spread of rubble extends roughly 25 metres in one direction and 15 in the other, noticeably sparser than comparable remains at other stations along the same coast, which tends to confirm that this hill was quietly quarried of its military architecture by local builders with more pressing needs than posterity.

The tower was built around 1805 to 1806, one of more than eighty such stations commissioned by the British Board of Ordnance in response to the genuine threat of a French invasion fleet arriving on Irish shores. Each station used a naval signal post, a mast-and-flag arrangement borrowed from shipboard practice, to pass messages along the chain. The system ran clockwise from Dublin Bay all the way to Malin Head in County Donegal, forming an unbroken coastal telegraph. On a clear day from Cnoc an Choillín, the well-preserved signal tower on Lettermullan Island, about 12.5 kilometres to the southeast, is still visible, making the old line of communication almost imaginable. The tower at Bunowen Hill to the northwest, roughly 19.9 kilometres away, has been demolished entirely and can no longer be seen. By the mid-1810s, with Napoleon's ambitions curtailed and the invasion threat fading, the whole system was abandoned. The Cnoc an Choillín station had little time to accumulate much of a history beyond its basic function.

The hill is accessed most easily via a natural cleft on the northeast side, running roughly north-northwest to south-southeast up through the granite. The summit itself is open blanket bog studded with rock outcrops, and the tower site sits just below the very top, with clear sightlines in almost every direction. A short distance to the west of the hill lies Tobar Muire, a holy well known locally by that name, and the village of Carna is about 1.18 kilometres to the southeast. Scattered stone alignments around the rubble spread may represent the remnants of a small enclosure or outbuildings that once surrounded the tower, though the remains are too fragmentary to read with any confidence on the ground.