137 Wiltshire From The Wikipedia

Wiltshire is a mostly rural landscape and about two thirds of the county lies on chalk, giving it a high chalk downland landscape. This chalk is part of the Southern England Chalk Formation that underlies large areas of Southern England from the Dorset Downs in the west to Dover in the east. The largest area of chalk in Wiltshire is Salisbury Plain, a vast expanse of semi-wilderness used mainly for arable agriculture and by the British Army as training ranges. The highest point of the county is Mill Hill on Salisbury Plain, at 295m/968ft.

As well as Salisbury Plain the chalk runs north east into Berkshire in the Marlborough Downs ridge, and south-west into Dorset as Cranborne Chase. Cranborne Chase, which straddles the border, has, like Salisbury Plain, yielded much stone age and bronze age archaeology. The Marlborough Downs are part of the North Wessex Downs AONB (Area of Outstanding Natural Beauty), a 1,730 sq km (668 square mile) conservation area.

Between the areas of chalk and limestone downland are clay valleys and vales. The largest of these vales is the Avon Vale. The Avon cuts diagonally through the north of the county, flowing through Bradford-upon-Avon and into Bath and Bristol. The Vale of Pewsey has been cut through the chalk into Greensand and Oxford Clay in the centre of the county. In the south west of the county is the Vale of Wardour. The south east of the county lies on the sandy soils of the New Forest.

Chalk is a porous rock so the chalk hills have little surface water. The main settlements in the county are therefore situated at wet points. Notably, Salisbury is situated between the chalk of Salisbury Plain and marshy flood plains.

Source: wikipedia.org