The reserve lies at around 250m above sea level on the dip slope of the Wharncliffe Rock (a Coal Measures sandstone), to the east of Wharncliffe Crags (which outcrop at the western edge of the site). In the eastern half of the reserve the topography dips gently eastward and northward toward a (northward flowing) narrow stream in the shallow valley bottom. East of the stream the ground slopes up toward a ridge of Grenoside Sandstone, known locally as ‘The Height’, which lies to the east of the reserve.
Where Wharncliffe Crags pass through the site this area is designated as a Site of Special Scientific Interest (SSSI) for geology. The area encompassed by the SSSI comprises the type section and best available exposure of Wharncliffe Rock, with this rock laid down approximately 313 million years before present, during the Langsettian period. Wharncliffe Rock comprises one of the important sandstone bodies in the 'Pennine Lower Coal Measures Formation'. The exposure of the Wharncliffe Rock, where it forms the Wharncliffe Crags, is a vertical cross section through a preserved fluvial (river) channel. The lateral continuity of the outcrop of the Wharncliffe Rock along the present day land surface is limited, thinning on both sides and it has disappeared altogether before Owlerton (southeast) and Penistone (northwest) are reached.
The area is close to the western boundary of the Yorkshire and East Midlands Coal Field. Below the Wharncliffe Rock there are several thin beds of coal, underlain by fireclay and ganister. Ganister, also referred in the ‘History’ section of this website, was of particular economic valuable (far greater than the thin coals), comprising an uncommon material for which West Sheffield is the type locality.
Courtesy of David Buttle