Massive sandstone rock formations tower 800 meters above Zion canyon in Zion National Park in Utah, USA. Zion's monoliths are composed of nine distinct, exposed and uplifted layers of sediments which are part of the Grand Staircase, an immense sequence of sedimentary rock layers that stretches 200 kilometres from Bryce Canyon to the grand Canyon in the American Southwest. Here in Zion, the layers were laid down overt a 150 million year period before they were thrust upward by the forces of plate tectonics and carved by erosion. Famous for its spectacular scenery, the 24 kilometre-long valley attracts more than three million visitors from throughout the world each year.