Valley of the Kings rains. There is currently little year-round rain in this part of Egypt, but there are occasional flash floods that hit the valley, dumping tons of debris into the open tombs. The quality of the rock in the Valley is inconsistent, ranging from finely-grained to coarse stone, the latter with the potential to be structurally unsound. The occasional layer of shale also caused construction and conservation difficulties, as this rock expands in the presence of water, forcing apart the stone surrounding it. It is thought that some tombs were altered in shape and size depending on the types of rock the
Valley of the Kings World Heritage Site, along with the rest of the Theban Necropolis. Exploration, excavation and conservation continues in the valley, and a new tourist centre has recently been opened. 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-Bahri, interspersed with soft layers of marl. The sedimentary rock was originally deposited between 35–56 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