Sossusvlei is a salt and clay pan surrounded by high red dunes, located in the southern part of the Namib Desert, in the Namib-Naukluft National Park of Namibia. The name "Sossusvlei" is often used in an extended meaning to refer to the surrounding area (including other neighbouring vleis such as Deadvlei and other high dunes), which is one of the major visitor attractions of Namibia. The name "Sossusvlei" is of mixed origin and roughly means "dead-end marsh". Vlei is the Afrikaans word for "marsh", while "sossus" is Nama for "no return" or "dead end". Sossusvlei owes this name to the fact that it is an endorheic drainage basin (i.e., a drainage basin without outflows) for the ephemeral Tsauchab River. This area is characterized by high sand dunes of vivid pink-to-orange color, an indication of a high concentration of iron in the sand and consequent oxidation processes. The oldest dunes are those of a more intense reddish color. These dunes are among the highest in the world; many of them are above 200 metres, the highest being the one nicknamed Big Daddy, about 325 metres high, however the highest dune in the Namib Desert, Dune 7, is about 388 metres high.