The AONB covers an area of some . It takes the form of a horseshoe, with the open end facing east, surrounding the town of
Newbury and the
River Kennet catchment area. The northern arm reaches as far east as the suburbs of
Reading in mid-
Berkshire and as far north as
Didcot in
South Oxfordshire, whilst the southern arm extends to
Basingstoke in northern
Hampshire. To the west, the AONB reaches as far as
Calne and
Devizes. The highest points are the 297 m (974 ft) summit of
Walbury Hill, situated southeast of
Hungerford in
West Berkshire (and the highest point in southern England east of the
Mendip Hills), and the
Milk Hill-
Tan Hill plateau northeast of
Devizes in central
Wiltshire, at 295 m (968 ft) above sea level. At its northeast extreme,
Lardon Chase within the North Wessex Downs AONB faces across the
Goring Gap to the
Chilterns AONB on the other side of the
River Thames. From here working anti-clockwise around the horseshoe, the Berkshire Downs have a steep
scarp slope facing north over the
Vale of White Horse and a gentler
dip slope facing south into the valley of the Kennet. This area includes the horse-racing village of
Lambourn and is hence sometimes known as the Lambourn Downs. Beyond the town of
Marlborough the downs (now called the Marlborough Downs) sweep in a semicircle to the south around the headwaters of the River Kennet, with the Vale of Pewsey cutting through these downs carrying the headwaters of the
Hampshire River Avon. Here too can be found the wooded area of
Savernake Forest. Finally, the highest stretch of the Downs runs east along the Berkshire-Hampshire border on the opposite side of the River Kennet from the Berkshire Downs. Again the scarp slope is to the north (facing down in the valley of the Kennet) and the dip slope is to the south into Hampshire.
Principal summits Hills within the National Landscape with more than 30 metres of topographic prominence are listed below. Twenty-five of these summits lie within the
Berkshire and
Marlborough Downs National Character Area (all of whose summits fall within the NL). Summits 1, 5, 11, 14, 16, 25, 27 and 28 are within the
Hampshire Downs, summits 10, 21 and 24 are within
Salisbury Plain and West Wiltshire Downs, summits 36, 37, 38, 39, 40 and 41 are within the
Thames Basin Heaths, summit 42 is within the
Upper Thames Clay Vales and summit 44 is within the
Thames Valley. == Geology and natural history ==