The painted hills are full of fossils of vertebrates including prehistoric horses, early elephants and rhinos, camels, sabre-toothed tigers and crocodiles roaming amongst a dense tropical forest against a background of volcanoes. The layers are coloured black, grey, red and yellow. The black layers are lignite, a type of soft coal that has been formed from the peat created as the dense vegetation died and partially rotted. The grey layers are formed from mudstones and shales that were laid down as the area was periodically covered by the sea. The main colours are reds and yellows, these represent the soil that was formed from volcanic ash.