In the Shadow of the Sabertooth: Global Warming, the Origins of the First Americans and the Terrible Beasts of the Pleistocene.
The habitat requirements of elk and their speed of migration are probably the same today as at the end of the Pleistocene.
But proponents of the so-called paleo lifestyle are taking it back a bit further—all the way to the Pleistocene.
The earlier of the two epochs of the Quaternary Period, from about 2 million to 10,000 years ago. The Pleistocene Epoch was characterized by the formation of widespread glaciers in the Northern Hemisphere and by the appearance of humans. Mammals included both small forms, such as saber-toothed tigers and horses and giant ones, such as mammoths and mastodons. Almost all the giant mammals, including woolly mammoths, giant wolves, giant ground sloths, and massive wombats disappeared at the end of the Pleistocene and the start of the Holocene. See Chart at geologic time.