Torc Waterfall sits on a geological fault called the Muckross to Millstreet Fault Line. Torc Mountain consists of 400 million-year-old Devonian Old Red Sandstone, but the base around Muckross Lake is circa 100 million years younger and consists of Carboniferous Limestone. At some stage, after the limestone was deposited, a period of tectonic-plate collision occurred and the land under Torc was lifted up 3,000 metres, re-exposing the underlying older sandstone.