The first inhabitants of North America arrived in Canada at least 14,000 years ago. It is believed the inhabitants entered the Americas pursuing Pleistocene mammals such as the giant beaver, steppe wisent, musk ox, mastodons, woolly mammoths and ancient reindeer (early caribou). One route hypothesized is that people walked south by way of an ice-free corridor on the east side of the Rocky Mountains, and then fanned out across North America before continuing on to South America. The other conjectured route is that they migrated, either on foot or using primitive boats, down the Pacific Coast to the tip of South America, and then crossed the Rockies and Andes. Evidence of the latter has been covered by a sea level rise of hundreds of metres following the last ice age.