The sandstones are red beds laid down by rivers and lakes in a landscape of low rocky hills. A great thickness of red sandstone, brought in by rivers, buried the old hills. This took place in the Proterozoic, 1,200 to 544 million years ago (mya). There are older and younger sandstone groups, with a long period between them. The lower sandstone is a breccia, with broken fragments of earlier rocks.