This ancient monolith, nearly square in plan and measuring 1.9 metres high with a base width of 0.55 metres, occupies a commanding position between Knockastoller Lough to the north and the Gweedore river to the south. The Irish name, which appears on maps as Cnoc An Stollaire, reflects the stone's long connection to this particular hillside.

The standing stone's prominent placement wasn't accidental; prehistoric peoples throughout Ireland often chose elevated spots that offered wide views across the surrounding countryside. While the exact purpose of Cloghastoller remains unknown, similar stones across Ireland have been interpreted as territorial markers, commemorative monuments, or ritual sites. Some may have served astronomical functions, marking important solar or lunar events for ancient farming communities.

The details about Cloghastoller come from the comprehensive Archaeological Survey of County Donegal, compiled by Brian Lacey and his team in 1983. This exhaustive catalogue documented field antiquities across the county, from Mesolithic sites through to 17th century structures, ensuring that monuments like this standing stone are properly recorded for future generations. Though weathered by centuries of Atlantic storms, the stone continues to mark this spot as it has done since the Bronze Age, a silent witness to the changing fortunes of this corner of Donegal.