Pembrokeshire's diverse range of geological features was a key factor in the establishment of the Pembrokeshire Coast National Park and a number of sites of special scientific interest (SSSIs). In the north of the county are the Preseli Hills, a wide stretch of high moorland supporting sheep farming and some forestry, with many prehistoric sites and the probable source of the bluestones used in the construction of the inner circle of Stonehenge in England. The highest point is Foel Cwmcerwyn at , which is also the highest point in Pembrokeshire. Elsewhere in the county most of the land (86 per cent according to CORINE) is used for farming, compared with 60 per cent for Wales as a whole.