This extremely arid ecoregion comprises shifting sand dunes, gravel plains and rugged mountains. The world's oldest desert, the Namib Desert has existed for at least 55 million years, completely devoid of surface water but bisected by several dry riverbeds. These riverbeds are vegetated and are home to a few ungulates, such as Hartmann's zebras. The south of the desert is extremely dry and even lacks dry riverbeds; gemsbok is the only large mammal to occur in this harsh environment. Thick fogs are frequent along the coast and are the life-blood of the desert, providing enough moisture for a number of interesting, highly-adapted animal species to survive. The Namib Desert is well protected in a series of National Parks, Recreation Areas and Protected Diamond Areas. The diamond areas require more formal protection when the lease on these areas expires in 2020.