Hidden beneath the slopes of a lush forest in Alberta, Canada, is a mass grave on a monumental scale.
Thousands of dinosaurs were buried there, killed in an instant on a day of utter devastation.
A group of paleontologists have come to Pipestone Creek - appropriately nicknamed the “River of Death” - to help solve a 72-million-year-old enigma: how did they die?
According to a report by BBC, trying to work out exactly what happened there starts with the hefty strike of a sledgehammer.
Brute force is needed to crack open the thick layer of rock that covers what Professor Emily Bamforth, who's leading the dig, described as "palaeo gold."
As her team begins the more delicate job of removing the layers of dirt and dust, a jumble of fossilized bones slowly begins to emerge.
The fossils in the small patch of ground that the team are working on are incredibly tightly packed. Bamforth estimates there are up to 300 bones in every square meter.
Thousands of fossils have been collected from the site, and are constantly generating new discoveries.
Paleontologists believe the dinosaurs were migrating together in a colossal herd for hundreds of miles from the south - where they had spent the winter - to the north for the summer.
Paleontologist Jackson Sweder is particularly interested in what looks like a chunk of dinosaur skull. “Most of what we find here is a duck-billed dinosaur called Edmontosaurus. If this is a skull bone, this is a dinosaur that's large - probably 30ft (10m) long,” he said.
Sweder is the collection manager at the Philip J Currie Dinosaur Museum in nearby Grande Prairie, where the bones from both of these giants are taken to be cleaned up and analyzed. He is currently working on a huge Pachyrhinosaurus skull that's about 1.5m long and has been nicknamed “Big Sam.”
All the evidence suggests that this catastrophic event was a flash flood - perhaps a storm over the mountains that sent an unstoppable torrent of water towards the herd, ripping trees from their roots and shifting boulders.
“We know, every time we come here, it's 100% guaranteed we'll find bones. And every year we discover something new about the species,” said Bamforth.
As the team packs up their tools ready to return another day, they know there's a lot of work ahead. They've only just scratched the surface of what's here - and there are many more prehistoric secrets just waiting to be revealed.
