The 63 Sites of Special Scientific Interest in Cheshire cover a total area of 19,844 hectares (49,035 acres), and are protected by law for their biological, geological or geomorphological interest. Wetland is the type of SSSI best represented in the county, with a range of diverse habitats including mosses, raised bog, swamps, fens, meres and ponds. Flashes, such as Elton Flashes (pictured), originate in subsidence after salt extraction, and contain rare examples of inland salt marsh. Cheshire's largest SSSIs are the Mersey and Dee estuaries.
The higher ground at the foot of the Pennines has two extensive SSSIs containing heather moorland, grassland and blanket mire habitats. The lowland heath habitat is, however, very rare. Ancient woodland is sparse in the county, but is found on the slopes of the Mid Cheshire Ridge, in river valleys towards the north of the county, and around the Mersey Basin. Several sites, such as Rixton Clay Pits, are on former industrial land. The Triassic sandstones of the Mid Cheshire Ridge are exposed at the Raw Head geological site, and geological features are also exposed at railway cuttings.