Stokenchurch Gap

The Stokenchurch Gap, also known as the Aston Rowant Cutting or Aston Hill cutting (from the nearby village of Aston Rowant), or locally "The Canyon" is a steep chalk cutting, constructed through the Chiltern Hills in Oxfordshire, England during the early 1970s for the M40 motorway. It is 1,200 metres long and a maximum of 47 metres deep, and is located approximately eight miles (13 km) from High Wycombe and close to the village of Stokenchurch. Despite the names, the cutting is in the parish of Lewknor rather than Aston Rowant or Stokenchurch.

The cutting is mainly through the Upper Chalk, with some Middle Chalk seen at its base. The cutting is a Site of Special Scientific Interest of geological importance. It provides the best Coniacian section in central England.

The curved route of the cutting was designed to mitigate impact on the skyline, and to fit the local topography. The construction of this section of the M40 (junctions 5–8) was at the time extremely controversial, since the cutting through the Chiltern Hills was driven through the middle of the ecologically-important Aston Rowant NNR. Conservation groups were appalled at the unexpected decision of the inspector at the public inquiry to reject their claims that the national nature reserve designation implied a fully protected landscape which should in no circumstances be damaged. Their alternative proposals for a tunnelled solution, or a route on-line with the existing A40, were rejected.

To a great degree, the inspector's decision, and the subsequent endorsement of that decision by the Secretary of State, proved a "wake-up" call to conservation groups across the country, so that when a similar case arose in the 1980s regarding the Winchester-Bypass section of the M3 at Twyford Down a far more robust — though ultimately unsuccessful — response was forthcoming.

...
Wikipedia