The reason Uluru rises so dramatically from the surrounding plain is because it is a monolith – that is, a single piece of rock, with most of its bulk hidden below ground like an iceberg. With few cracks to be exploited by weathering, and the layers of very hard, coarse-grained sandstone (or arkose) tilted to a near-vertical plane, the Rock has resisted the denudation of the landscape surrounding it. However, wind and rain have had their effects. During storms, brief, but spectacular, waterfalls stream down the rock forming dirty channels. In places, the surface of the monolith has peeled or worn away, producing bizarre features and many caves, most out of bounds but some accessible on the walking trails. The striking orangey-red hue is actually superficial, the result of oxidation (“rusting”) of the normally grey sandstone that can still be seen in some nooks and caves.