Exmoor is an area of hilly open moorland in west Somerset and north Devon in South West England, named after the main river that flows out of the district, The River Exe. The moor has given its name to a National Park, which includes the Brendon Hills, the East Lyn Valley, the Vale of Porlock and 55 kilometres (34 mi) of the Bristol Channel coast. The total area of The Park is 692.8 square kilometres (267.5 sq mi), of which 71% is in Somerset and 29% in Devon.
The National Park is primarily an upland area with a dispersed population living mainly in small villages and hamlets. The largest settlements are Porlock, Dulverton, Lynton, and Lynmouth, which together contain almost 40% of the park's population. Lynton and Lynmouth are combined into one parish and are connected by the Lynton and Lynmouth Cliff Railway.Exmoor was once a Royal forest and hunting ground, which was sold off in 1818. This title earns the site some legal protection from development, damage and neglect.
Exmoor is an upland of sedimentary rocks classified as gritstones, sandstones, slate, shale and limestone, siltstones, and mudstones depending on the particle size. They are largely from the Devonian and early Carboniferous periods . As this area of Britain was not subject to glaciation, the plateau remains as a remarkably old landform. Quartz and iron mineralisation can be detected in outcrops and subsoil.
The Glenthorne area demonstrates the Trentishoe Formation of the Hangman Sandstone Group. The Hangman Sandstone represents the Middle Devonian sequence of North Devon and Somerset. These unusual freshwater deposits in the Hangman Grits, were mainly formed in desert conditions. The underlying rocks are covered by moors and supported by wet, acid soil. The highest point on Exmoor is Dunkery Beacon; at 519 metres (1,703 ft) it is also the highest point in Somerset.