Cheddar is a gorge lying on the southern edge of the Mendip Hills. The maximum depth of the gorge is 137 m (449 ft), with a near-vertical cliff-face to the south, and steep grassy slopes to the north. The B3135 road runs along the bottom of the gorge.
The area is underlain by Black Rock slate, Burrington Oolite and Clifton Down Limestone of the Carboniferous Limestone Series, which contain ooliths and fossil debris, on top of Old Red Sandstone and by dolomitic conglomerate of the Keuper. Evidence for Variscan orogeny is seen in the sheared rock and cleaved shales. In many places weathering of these strata has resulted in the formation of immature calcareous soils.
The gorge was formed by meltwater floods during the cold periglacial periods which have occurred over the last 1.2 million years. During the ice ages permafrost blocked the caves with ice and frozen mud and made the limestone impermeable. When this melted during the summers, water was forced to flow on the surface, and carved out the gorge. During warmer periods the water flowed underground through the permeable limestone, creating the caves and leaving the gorge dry, so that today much of the gorge has no river until the underground Cheddar Yeo river emerges in the lower part from Gough's Cave. The river is used by Bristol Water, who maintain a series of dams and ponds which supply the nearby Cheddar Reservoir, via a 137-centimetre (54 in) diameter pipe that takes water just upstream of the Rotary Club Sensory Garden, a public park in the gorge opposite Jacob's Ladder.
