This site is located west of the village of Dunfanaghy, in northern Co. Donegal. The bedrock geology is dominated by quartzite (which forms the cliffs of Horn Head) interbedded with smaller amounts of schist and metadolerite bedrock elsewhere. Extensive sand areas dominate the southwestern and eastern portions of the site, while peat podsols predominate in the north, with occasional rocky outcrops. New Lake is a slightly brackish body of water that was formed in the 1920s when aeolian deposits of sand (from the dunes to the west) blocked the outlet connecting Rinclevan Strand to the sea. The site comprises a complex of habitats of which open marine areas, sea cliffs, sand dunes (several types), peat bogs and heathland occupy the largest areas. Other habitats present include mud and sand intertidal flats, wet meadows, and improved grasslands. The main uses of the land within the ZEC are agriculture (mainly grazing), recreational activities and also the forest exploitation of the plantations.
The site is a SAC selected for the following habitats and/or species from Annexes I/II of Directive 92/43/EEC (priority types are indicated with an asterisk, the area in hectares is shown in parentheses):
2110 Embryonic Shifting Dunes (0.39)
2120 Marram Dunes (White Dunes) (5.18)
*2130 Fixed Dunes (Grey Dunes) (292.33)
2170 Dunes with Creeping Willow (9.04)
2190 Humid Dune Slacks (42.57)
*21A0 Machairs (41.32)
3130 Oligotrophic to Mesotrophic Standing Waters (23.94)
1013 Geyer's Whorl Snail (Vertigo geyeri)
1364 Gray Seal (Halichoerus grypus)
1395 Petalwort (Petalophyllum ralfsii)
1833 Slender Naiad (Najas flexilis)
In the southwestern part of the site is a dune system that is impressive in terms of its size, variety of dune types, and lack of disturbance. The 2110 embryonic dunes are found as a thin strip along the margins of the 2120 dunes that are up to 30 m wide and can reach up to 8 m in height. Of particular interest is the area of fixed dunes northeast of the village of Dunfanaghy and northeast of Trawmore, especially at Lurgabrack. The dominant vascular plant species are Festuca rubra, Ammophila arenaria and Galium verum, accompanied by species including Trifolium pratense, Lotus corniculatu) and Viola tricolor subsp. curtisii. A nationally rare plant species, Thalictrum minus, has been confirmed in fixed dune areas in Lurgabrack.
The bryophyte component of the vegetation is very well developed, with species such as Tortula ruraliformis, Pleurozium schreberi and Homalothecium lutescens being particularly abundant. In addition to the commonly found mosses, a number of rarer bryophytes have also been recorded from the fixed dunes around Dunfanaghy. These include Thuidium abietinum, Bryum marratii, and Distichum inclinatum. Habitats 2190 and 2170 are very extensive, with this site hosting the largest area of wet dune depressions in Ireland. The smaller depressions are variable in their flora, while the larger one houses communities of high floristic richness.
Habitat 21A0*, whose distribution in the EU is restricted to Ireland, is located in the north-west of the site. Port Lough, a mesotrophic to oligotrophic lake of good water quality, has a diverse flora and is home to a significant population of Najas flexilis. This species is included in Annex II of Directive 92/43/EEC and is also legally protected by the Flora Protection Order of 1999.
The dunes are bounded by rocky headlands with grasslands and heathland to the east and west. On rocky cliffs (maximum height 207 m), exposure is a limiting factor for plant growth, but where soil has accumulated, marine plants such as Armeria maritima, Silene vulgaris subsp. maritima and Crithmum maritimum. Two rare bryophytes (Acrobolbus wilsonii and Geocalyx graveolens) have been recorded from Horn Head Cliffs, as have two species of flowering plants listed in the Irish Red Book, Agrostemma githago and Ligusticum scoticum. Inland from the cliffs are hills that support lush vegetation dominated by heather (Calluna vulgaris).
The cliffs at Horn Head are of great importance to seabirds, supporting an internationally important population of Alca torda and nationally important populations of Fulmarus glacilis, Rissa tridactyla and Uria aalge. The Falco peregrinus and Pyrrhocorax pyrrhocorax species listed in Annex I of Directive 2009/147/EC breed on the site. Regular wintering populations of Cygnus cygnus, Anser albifrons flavirostris, and Branta leucopsis (the latter two of national importance) are found, along with a variety of other waterfowl species. Breeding waders are also found, notably Calidris alpina, a Red Book species. A small to medium sized population of Halichoerus grypus is also home to it.