Uluru and Kata Tjuta started to form about 550 million years ago.

Back then, the Petermann Ranges to the west of Kata Tjuta were much taller than they are now. Rainwater flowed down the mountains, eroding sand and rock and dropping it in big fan shapes on the plains. One fan was mainly water-smoothed rock while the other was mostly sand.

Around 500 million years ago, the whole area became covered in sea. Sand and mud fell to the bottom and covered the seabed, including these fans. The weight of the new seabed turned the fans into rock. The sandy fan became sandstone (Uluru) while the rocky fan became conglomerate rock (Kata Tjuta).

400 million years ago, the sea disappeared. Rocks folded and tilted as the earth’s tectonic plates shifted. Kata Tjuta tilted slightly and Uluru tilted 90 degrees.

Over the last 300 million years, the softer rocks eroded away, leaving the spectacular forms of Uluru and Kata Tjuta behind.

Uluru is a type of rock called arkose. If you take the base walk you can see that the surface is actually flaky red with grey patches. The flakes are bits of rock left after water and oxygen have decayed minerals in the rock. The red is the rusting of iron found naturally in arkose, and the grey is the rock’s original colour. You can see Uluru’s original grey inside many of its caves.

Kata Tjuta is made from a conglomerate of pebbles and boulders cemented by sand and mud. Most of the pieces are granite and basalt, which give the conglomerate a plum-pudding effect.

These magnificent rock formations are actually a lot bigger than they appear – like icebergs, most of their mass is below the surface. Uluru and Kata Tjuta are only the tips of huge rock slabs that continue underground for up to 6 km!

Download our fact sheet to learn more about the area’s geology.