The park is in a geological area called the Amadeus sedimentary basin. The basin was formed about 900 million years ago. Over hundreds of millions of years, it was covered by layer after layer of sediment, until about 300 million years ago. About 550 million years ago, the mountain ranges to the south and west were pushed up out of the ground in a mountain-building event. These mountains quickly crumbled and huge chunks of sediment were pushed northward by rivers. The rivers flattened out into at least two alluvial fans. It is the remains of these alluvial fans that are seen today as Uluṟu and Kata Tjuṯa.