The Chiltern Hills are a range of hills to the north west of London.
From the outskirts of London the Chilterns rise to their northern escarpment overlooking the Vale of Aylesbury, their highest point being some 265 metres above sea level at Haddington Hill near Wendover.
The Chiltern Hills stretch northeastward from the Wiltshire Downs and the River Thames West of London up towards Luton and the Dunstable Downs to the North of London.
The Chilterns are characterised by their chalk downs and beechwoods. Chalk streams such as the River Misbourne and River Chess run through the valleys.
The chalk rock that makes up the Chilterns was formed more than 100 million years ago, when the entire area lay beneath a vast shallow ocean, as layer upon layer of marine sediment built up.
Over time the incalculable forces of the earths shifting tectonic plates lifted and folded the chalk rock which was then very gradually eroded resulting in the gently undulating hills we see today.
At the same time the softer clay surrounding the Chilterns was more easily eroded, though these lower fertile vales were less permeable and ideal for farming.
The porous and permeable uplands of the Chiltern Hills readily absorb surface water. Unless trapped by man-made or naturally occuring clay-lined ponds the water only comes to the surface where the underlying water table is higher than the chalk hills. These natural aquifers feed the chalk streams so characteristic of the Chiltern Hills.
Traditionally the chalky grasslands covering the hills have long been used as grazing for sheep and cattle.
The beechwoods of the Chiltern Hills have for centuries fostered the furniture trade, especially chair making centred around the town of High Wycombe.