This vast stretch of desert is home to some amazing brightly coloured tree trunks. More than 225 million years old, these trees, some of which are several feet long, were buried under volcanic ash and sediment deposits. Gradually, erosion has revealed these astonishing fossils situated in the thick sedimentary layer, which has also resulted in the badlands of the Painted Desert. The pastel-coloured hills here are a stunning sight at sunrise and sunset, when they come alight with red and orange hues.