Chalk extends throughout much of Hertfordshire providing much of the prominent relief of the Chiltern Hills. However, there are also important and unique examples of Tertiary (Hertfordshire Puddingstone) and Pleistocene sediments in the County, and evidence of glacial and periglacial environments. Ice and water have moulded the landscape which is also reflected in the locations designated as either Regionally Important Geological and Geomorphological Sites (RIGS) or Sites of Special Scientific Interest (SSSI).

We take an active interest in conserving important geological sites in Hertfordshire and working parties are regularly organised to clean up and preserve these SSSIs and RIGS.