The youngest rock to be found in the geopark area is a dolerite dyke of Tertiary age at Hog's Head. This is an igneous rock formed from molten rock approximately 20 mya. It intruded into the surrounding rocks cutting its way vertically upwards as a 5 metre wide body. This type of rock is not seen anywhere else on the peninsula but geographical evidence traces it from Smerwick Harbour on the Dingle Peninsula to Glengarriff in West Cork. The dyke can be viewed clearly from the main road at Loher.