Pattern on a sandstone boulder sculpted by wind erosion. Wadi al-Hitan in the Sahara desert.

Patterns on a sandstone boulder shaped by the wind erosion (aeolian processes) at Wadi al-Hitan, the Valley of the Whales in the Sahara desert in Egypt. Wadi al-Hitan, the Whale Valley, is a UNESCO World Heritage Site known for its great number of fossils, particularly those of the early forms of whales called Archaeoceti, the mammals that lived here in Eocene. They make Wadi al-Hitan a very significant site for the history of evolution.