Translated as Friaochs carn, it was the inaugeration site of the O’Connor clan in Connaught.
From Wikipedia
It is a small mound about one and a half meters high that sinks slightly at the top and is covered on one side by a dressing of stone. Up until the mid-nineteenth century a proclamation stone stood nearby that featured two sunken footprints, the stone now resides at Clonalis House near Castlerea.
Regarding the inaugeration stone archaeology.ie has this to say
When a portion was broken off the inauguration stone of the O’Conor kings at Carnfree (RO028-69001-) it was moved to the avenue of Cargin House near Tulsk c. 1840 by Daniel Kelly to prevent further damage by quarrying at the original site (Jones 1922-3). It has since been moved to the grounds of Clonalis House in the 1970s, although its authenticity is doubtful (FitzPatrick 2004, 113-5). Roughly rectangular limestone block (dims. of base 0.8m x 0.4m; H 0.45-0.55m) with a subrectangular upper surface (dims. 0.9m x 0.35-0.6m) which has an oval hollow (dims. 0.3 x 0.1m; D 0.7m) divided in two by a ridge at the base to represent a footprint.