[3] The hills support an extensive range of wildlife leading to the designation of 16 Sites of Special Scientific Interest (SSSIs).

The hills are crossed by a network of minor roads with major transport routes including the M5 motorway running around the periphery.

[4][5][6] Straddling the border of Somerset and Devon, the Blackdown Hills AONB covers an area of 370 square kilometres (143 sq mi).

The Permian and Triassic sandstone aquifer in the Otter Valley is one of Devon's largest groundwater sources, supplying drinking water to Taunton.

Villages in the northern, Somerset part of the hills include Staple Fitzpaine, Buckland St Mary, Whitestaunton, Wambrook and Churchstanton.

The larger, more southerly area in Devon includes Dunkeswell, Luppitt, Upottery, Smeatharpe, Hemyock, Blackborough, Yarcombe, Membury, Stockland, Sheldon, Cotleigh and Chardstock.

The geology of the Blackdown Hills together with the adjoining East Devon AONB is unique in south-west England,[11][12] forming part of the only extensive outcrop of Upper Greensand in the region.

[13] The Blackdown Hills form a flat plateau dominated by hard chert bands, made up of clay with flints, of Upper Greensand with some remnants of chalk.

[15] In the western areas the Upper Greensand is devoid of calcareous material but the sands yield fossils of marine bivalves and gastropods (snails) preserved in silica.

Typically there are patchy deposits of head (clays, sands and gravels of local origin) found beneath the affected sections of slopes.

The mean temperature is approximately 10 °C (50 °F) and shows a seasonal and a diurnal variation, but because of the modifying effect of the sea the range is less than in most other parts of the United Kingdom.

[22] There are 16 Sites of Special Scientific Interest (SSSIs) in the Blackdown Hills ranging from the 156-hectare (390-acre) Black Down and Sampford Commons to Reed Farm pit at just less than 1-hectare (2.5-acre).

The flora includes the heath spotted-orchid (Dactylorhiza maculata), corky fruited water dropwort (Oenanthe pimpinelloides), green-winged orchid (Anacamptis morio), heather (Calluna vulgaris), lousewort (Pedicularis sylvatica) and bird's-foot trefoil (Lotus corniculatus).

The hedgerows and woodlands are made up of ash, hazel (Corylus avellana), grey willow (Salix cinerea) and pedunculate oak (Quercus robur) which support populations of hazel dormouse (Muscardinus avellanarius), common lizards, siskin, stinking iris (Iris foetidissima) and the purple hairstreak butterfly (Neozephyrus quercus).

The heathland supports a typical invertebrate fauna, including a wide variety of butterfly species, and with spiders notably abundant.

[25] Quants, a grassland clearing in a forestry plantation well known for its butterflies including Duke of Burgundy, marsh fritillary and wood white,[26] is a candidate for Special Area of Conservation (cSAC).

Paleoenvironmental studies have shown that organic material began to accumulate on the Blackdown Hills in the Mesolithic and Neolithic periods with areas of open meadow, grass land with small woodland components being identified.

The fort is situated on a promontory to the north of and overlooking the River Otter, Devon at approx 178 m (584 ft) above sea level.

[36] A Roman bath house and Edwardian folly in the village of Whitestaunton were excavated by the archaeological television programme Time Team.

[44] On 5 November 1380, King Richard II granted Sir William and Lady Margaret Asthorpe a licence to crenellate the Hemyock manor house, meaning the permission to fortify it.

[45] Over the centuries, Hemyock Castle had many notable owners including Lord Chief Justice Sir John Popham.

During the English Civil War it was held for Parliament, subjected to a brief but brutal siege and eventually slighted to destroy its military value.

[48] Coldharbour Mill was built around 1800 to exploit the available water power of the River Culm and was used for wool and yarn production until its commercial closure in 1981.

Until the end of his life Bevan continued to paint in the Bolham valley and nearby Luppitt his angular style sitting well with the strong patterning of the landscape.

[52] Dunkeswell Aerodrome (IATA: N/A, ICAO: EGTU) was built in the Second World War by the RAF, briefly used by the USAF, and then the Fleet Airwing 7 of the USN.

However, National Parks, unlike AONBs, have their own authorities and have special legal powers to prevent unsympathetic development.

The Bristol to Exeter line and the remains of the Grand Western Canal run, quite close in places, to the west of the M5 motorway but do not pass through the Blackdown Hills.

[56] Dunkeswell Aerodrome (IATA: N/A, ICAO: EGTU) is now a busy civilian airfield with a mix of light aircraft, microlights and parachuting.

Employment opportunities are concentrated in the surrounding towns and in a number of small-scale industrial parks — notably around Dunkeswell airfield.