|Site of Special Scientific Interest|
|Area||40.9 ha (101.1 acres)|
|Area of Search||County Durham|
|Website: Map of site|
Cassop Vale is a Site of Special Scientific Interest in the Durham City district of County Durham, England. It lies between the villages of Bowburn and Cassop, 7 km south-east of the centre of Durham..
The site is important as one of the larger areas of grassland developed on magnesium limestone. This rock has a restricted distribution in England and grassland associated with it is confined almost entirely to south-east Tyneside and County Durham, usually in small, scattered patches that are threatened by quarrying and modern agricultural practices.
Habitats at Cassop Vale include grassland, scrub, woodland and wetland, the last fed by spring-lines. The area also includes recolonised open quarries and mine spoil-heaps, which add to the floral diversity. Several rare and local species are present, including globeflower, Trollius europaeus, birds's-eye primrose, Primula farinosa, lesser club-moss, Selaginella selaginoides, and moonwort, Botrychium lunaria. The area also supports a diverse invertebrate fauna that includes populations of the Durham Argus butterfly, Aricia artaxerxes salmacis.