Uluru, also known as Ayers Rock is an island mountain or inselberg and this huge rock is very sacred to the Aborigines who live in the area. It is located in the middle of Australia and its formation began over 500 million years ago. Its composition is sedimentary rock called arkose, which is a sandstone--primarily composed of feldspar and some conglomerate and it was once part of an ancient sea floor. It is thought that rapid erosion of the mountains to the south provided the materials that were deposited under the sea which ultimately became the Uluru formation. The sands and gravels were so far down that they were changed from sediment to rock due to pressure of the layers above and were squeezed together. A later mountain building event further folded and compressed the rock. Eventually, the softer rock eroded away and what emerged is the Uluru which is made of a very welded--together rock. Due to the process of weathering, the top is now flat and the sides are grooved. When arkose is exposed to the atmosphere, some of its layers wear away more quickly than others resulting in parallel ribs or ridges. The red color of Uluru is due to rusting of the iron which is in the arkose. The rock reacts with water and oxygen over time. These are all examples of weathering. Water has also shaped valleys, formed caves, potholes and pools.