The upland areas of the Outer Hebrides, while neither as high nor as extensive as the adjacent upland areas of Skye or the west coast mainland, merit further investigation. There are isolated hills in the Uists and Barra, but the largest continuous upland area is formed by the hills of South Lewis/ North Harris, stretching in a belt from Lochs in the east, to the bold bare tops of Uig in the west of the island. The highest summit in the islands, the Clisham (799m), lies within this range, it has a conical shape which would have been caused by a moving ice cap, centred here in the last ice age.
The rock type of the Upland land areas is much the same as the rest of the Outer Hebrides, compromising different types of Lewisian gneiss. Some spectacular cliff formations exist in the Outer Hebrides, such as Sron Ulladale in North Harris, which is the biggest overhanging rock face in Britain.
Upland areas are covered in vast areas of exposed rock, as conditions for soil formation are poor. Steep slopes are often covered with scree. The upland area also show many good examples of ice-moulded topography, such as corries and V - shaped valleys giving way to fjords at the coast.
The mountain flora of the Outer Hebrides is limited in comparison to most of the rest of the Highlands, though there is an oceanic influence on these rugged, gale-swept hills. Vegetation tends to be sparse on the thin, nutrient poor soils of the higher areas, and is largely confined to grasses, mosses and lichens. The floristic composition is therefore strongly influenced by the surrounding dominance of the peatland habitat.
Throughout most of the uplands, the dominant land-use is unimproved grazing for sheep and/or deer. In a few localities the hill land is managed for grouse shooting by the annual burning of different strips of heather. A subsidiary land-use, growing in importance, is the recreational use of the hills. In the case of the Outer Hebrides this is largely reflected in hillwalking, with a little rock climbing on some cliffs in North Harris and Uig