The site, which follows the path of a section of Hadrian's Wall, is notable for an unusually wide range of grassland types growing on thin soil above the Whin Sill, a rock formation peculiar to the Northern Pennines.

It is an east-west corridor of land straddling Hadrian's Wall for a distance of 1 mile (1.6 km) between Milecastle 45 (Walltown) to the west, and Turret 43B in the east, just short of the fort of Aesica (Great Chesters).

[1][2] The site is situated on the Whin Sill, igneous rock dolerite found in County Durham and Northumberland, which outcrops as high, rocky cliff lines, and which was used by the builders of Hadrian's Wall to full strategic advantage.

[2] Grassland surrounding drier areas is composed of red fescue (Festuca rubra), common bent (Agrostis capillaris), sweet vernal-grass (Anthoxanthum odoratum), crested dog's-tail (Cynosurus cristatus) and heath grass (Danthonia decumbens).

Crags and north-facing scarp slopes support bilberry (Vaccinium myrtillus) and heather (Calluna vulgaris), fir clubmoss (Lycopodium selago) and parsley fern (Cryptogramma crispa).