Mole Gap to Reigate Escarpment and there are well developed river cliffs where alluvial fans have diverted the River Mole against the valley sides. Mole Gap to Reigate Escarpment Mole Gap to Reigate Escarpment is a biological and geological Site of Special Scientific Interest west of Reigate in Surrey. It is a Geological Conservation Review site and a Special Area of Conservation. Part of it is a Nature Conservation Review site, Grade I. Two small private nature reserves in the site are managed by the Surrey Wildlife Trust, Dawcombe and Fraser Down. This eight mile long site on the North Downs contains an outstanding range
River Mole the Pipp Brook, a tributary draining the northeastern slopes of Leith Hill. Between Dorking and Leatherhead the Mole cuts a steep-sided valley (the Mole Gap) though the North Downs, carving a river cliff on the western flank of Box Hill and a smaller cliff at Ham Bank in Norbury Park. The sudden change from impermeable Wealden Clay to permeable chalk and the increased gradient of the river (which drops in the stretch between Brockham and Leatherhead, compared to in between Horley and Brockham) allow the water table to drop below the bed of the river. Water is able to flow