The Sandstone Ridge is formed from layer upon layer of Triassic sandstones and pebble beds, deposited under arid conditions about 250 million years ago. Easily eroded, dramatic cliffs of reddish-pink sandstone can be discovered all along its length, indented with fissures and caves. The prevalent red colouration is due to the presence of iron oxides that form under dry conditions where periodic downpours are separated from long periods of drought. In places the red colouration has been modified to produce a mottled effect with red replaced by yellow or buff. This sandstone has provided much building stone locally for houses and walls and in the wider vicinity, for example, in Chester. No sandstone is extracted now, but overgrown quarries carved into the hillsides can be found throughout the Ridge.
In more recent geological time, copper and other metals were deposited from groundwater percolating along faults in the sandstone. Copper was in sufficient concentration to be mined in the south of the Ridge at Bickerton from around 1690 to the 1920s.
During the last ice age, the Ridge formed a barrier to the passage of the retreating ice sheets, and its hills are etched with numerous glacial meltwater channels. Particularly spectacular examples are those at Urchin's Kitchen in Primrosehill Woods and at Holbitch Slack near Cotebrook. As the ice receded it deposited huge quantities of glacial till on the lower slopes of the Ridge and surrounding plain. Meres and mosses have developed in natural depressions within this material, creating a watery landscape. The tail end of this material — the terminal moraine — comprised sands and gravels which are still extracted today around Delamere for use in the construction industry.