Karoo are exposed. These are locally known as the Cango Group, but are probably continuous with the Malmesbury Group that forms the base of Table Mountain on the Cape Peninsula, and similar outcrops in the Western Cape. In the Little Karoo, the outcrop is composed of limestone, into which an underground stream has carved the impressively extensive Cango Caves. The Great Karoo and Little Karoo lie almost entirely within two of South Africa’s eight botanical biomes, namely the Succulent Karoo biome and the Nama Karoo biome, both of which, like the Karoo Geological System, are more extensive than the geographical or
Karoo sediments. This exposed the dolerite sills, which were more resistant to erosion than the Karoo sediments, forming one of the most characteristic features of the Karoo landscape, namely the flat topped hills, called "Karoo Koppies". The geology of the region bears no resemblance to that of the Great Karoo (see the diagram on the left, of a NS geological cross-section through the Little and Great Karoos). The valley is an integral part of the Cape Fold Mountain Belt, with the two ranges on either side composed of extremely hard, erosion-resistant, quartzitic sandstone belonging to the 450- to 510-million-year-old Table Mountain