The rock strata on which Dorking sits, belong primarily to the Lower Greensand Group. This group is multilayered and includes the sandy Hythe Beds, the clayey Sandgate Beds and the quartz-rich Folkestone Beds. The lower greensand was deposited in the early Cretaceous, most likely in a shallow sea with low oxygen levels. Over the subsequent 50 million years, other strata were deposited on top of the Lower Greensand, including Gault clay, Upper Greensand and the chalk of the North and South Downs.

Following the Cretaceous, the sea covering the south of England began to retreat and the land was pushed higher. The Weald (the area covering modern-day south Surrey, south Kent, north Sussex and east Hampshire) was lifted by the same geological processes that created the Alps, resulting in an anticline which stretched across the English Channel to the Artois region of northern France. Initially an island, this dome-like structure was drained by the ancestors of the rivers which today cut through the North and South Downs, including the Mole. The dome was eroded away over the course of the Cenozoic, exposing the strata beneath and resulting in the escarpments of the Downs and the Greensand Ridge.