US scientists have produced their most precise date yet for the landslide that shaped the iconic canyon running through what is now Zion National Park.
The colossal rock avalanche occurred about 4,800 years ago, they say, based on a study of some of its boulders.
The researchers have also re-examined the details of the event.
They find the slide probably contained some 286 million cubic metres of debris – enough to cover New York’s Central Park to a depth of about 80m.
That volume dammed Zion Canyon’s Virgin River, creating a lake that remained for centuries.
As sediments filled this lake, they gave the valley its distinctive flat floor, which today makes it very easy to cross on foot.