Uluru, also known as Ayers Rock, is a large sandstone rock formation in the southern part of the Northern Territory in central Australia. It lies 335 km (208 mi) south west of the nearest large town, Alice Springs, 450 km (280 mi) by road. Kata Tjuta and Uluru are the two major features of the Uluṟu-Kata Tjuṯa National Park. Uluru is sacred to the Anangu, the Aboriginal people of the area. The area around the formation is home to an abundance of springs, waterholes, rock caves, and ancient paintings. Uluru is listed as a UNESCO World Heritage Site. Uluru is an inselberg, literally "island mountain". An inselberg is a prominent isolated residual knob or hill that rises abruptly from and is surrounded by extensive and relatively flat erosion lowlands in a hot, dry region. Uluru is also often referred to as a monolith, although this is a somewhat ambiguous term that is generally avoided by geologists. The remarkable feature of Uluru is its homogeneity and lack of jointing and parting at bedding surfaces, leading to the lack of development of scree slopes and soil. These characteristics led to its survival, while the surrounding rocks were eroded. For the purpose of mapping and describing the geological history of the area, geologists refer to the rock strata making up Uluru as the Mutitjulu Arkose, and it is one of many sedimentary formations filling the Amadeus Basin. The Mutitjulu Arkose is believed to be of about the same age as theconglomerate at Kata Tjuta, and to have a similar origin despite the rock type being different, but it is younger than the rocks exposed to the east atMount Conner, and unrelated to them.
The strata at Uluru are nearly vertical, dipping to the south west at 85°, and have an exposed thickness of at least 2,400 m (7,900 ft). The strata dip below the surrounding plain and no doubt extend well beyond Uluru in the subsurface, but the extent is not known. The rock was originally sand, deposited as part of an extensive alluvial fanthat extended out from the ancestors of the Musgrave, Mann andPetermann Ranges to the south and west, but separate from a nearby fan that deposited the sand, pebbles and cobbles that now make up Kata Tjuta. The similar mineral composition of the Mutitjulu Arkose and the granite ranges to the south is now explained. The ancestors of the ranges to the south were once much larger than the eroded remnants we see today. They were thrust up during a mountain building episode referred to as the Petermann Orogeny that took place in lateNeoproterozoic to early Cambrian times (550–530 Ma), and thus the Mutitjulu Arkose is believed to have been deposited at about the same time. The arkose sandstone which makes up the formation is composed of grains that show little sorting based on grain size, exhibit very little rounding and the feldspars in the rock are relatively fresh in appearance. This lack of sorting and grain rounding is typical of arkosic sandstones and is indicative of relatively rapid erosion from the granites of the growing mountains to the south. The layers of sand were nearly horizontal when deposited, but were tilted to their near vertical position during a later episode of mountain building, possibly the Alice Springs Orogeny of Palaeozoic age (400–300 Ma).