Every year, millions of people travel to Utah to take in the beautiful and peaceful scenery in Zion National Park. According to a new study, however, the geographic stunner was formed by a massive prehistoric landslide that was far from tranquil. The study, published Thursday in the Geological Society of America, said the park’s flat valley floor owes its creation to the collapse of a wall of Navajo Sandstone that was almost 900 miles high. Weak layers in the underlying Kayenta Formation sent debris shooting across the canyon at speeds that likely reached 90 miles per second. It's believed that...