The Karoo is a semi desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is also not precisely defined. The Karoo is partly defined by its topography, geology and climate, and above all, its low rainfall, arid air, cloudless skies, and extremes of heat and cold. The Karoo also hosted a well-preserved ecosystem hundreds of million years ago which is now represented by many fossils.
The Little Karoo’s boundaries are sharply defined by mountain ranges to the west, north, and south. The road between Uniondale and Willowmore is considered, by convention, to form the approximate arbitrary eastern extremity of the Little Karoo. Its extent is much smaller than that of the Great Karoo. Locally, it is usually called the Klein Karoo, which is Afrikaans for Little Karoo.
The Great Karoo straddles the 30° S parallel on the west of the continent, in a similar position to other semidesert areas on earth, north and south of the equator. It is furthermore in the rainfall shadow of the Cape Fold Mountains along the western coastline. The western "Lower Karoo" (the Tankwa Karoo and Moordenaarskaroo) contain remnants of the Cape Fold Mountains (e.g. the Witteberg and Anysberg Mountains) which give it a moderate hilly appearance, but further east, the Lower Karoo becomes a monotonously flat plain. The "Upper Karoo" has been intruded by dolerite sills (see below), creating multiple flat-topped hills, or Karoo Koppies, which are iconic of the Great Karoo.