The Burgess Shale is a series of sediment deposits spread over a vertical distance of hundreds of metres, extending laterally for at least 50 kilometres (30 mi).[19] The deposits were originally laid down on the floor of a shallow sea; during the Late Cretaceous Laramide orogeny, mountain-building processes squeezed the sediments upwards to their current position at around 2,500 metres (8,000 ft) elevation[5] in the Rocky Mountains.[20]