The various shades of red and white occur in the thin beds of siltstone and mudstone deposited on an ancient tidal flat about 220 million years ago. Thin layers of siltstone and shale each contining ripple marks, mudcracks, and rain imprints combine to tell the history recorded in the rock now exposed in this colorful cliff. The record of Earth’s history preserved in sedimentary rocks is truly remarkable. Each bedding plane is a remnant of what was once the surface of Earth. he geologic processes operating on Earth’s surface produce only subtle changes in the landscape during a human lifetime, but over a period of tens of thousands or millions of years, the effect of these processes is considerable. Given enough time, the erosive power of the hydrologic system can reduce an entire mountain range to a featureless lowland. In the process, the eroded debris is transported by rivers and deposited as new layers of sedimentary rock.