The Valley of the Kings is situated over 1,000 feet of limestone and other sedimentary rock, which form the cliffs in the valley and the nearby Deir el-Bahari, interspersed with soft layers of marl. The sedimentary rock was originally deposited between 35 and 56 million years ago during a time when the Mediterranean Sea sometimes extended as far south as Aswan. During the Pleistocene the valley was carved out of the plateau by steady rains. There is currently little year-round rain in this part of Egypt, but there are occasional flash floods that hit the valley. These floods dump tons of debris into the open tombs.