During the Pleistocene Ice Ages some mammal species had a large than life form. Cave bears were large in comparison to modern bears and giant elks roamed the temperate regions. We also had giant sloths, giant cats and beavers, and giant elephants. These were the mammoths.
At www.livescience.com/51424-woolly-mammoth-genome-sequenced.html … we learn that the genome of the woolly mammoths was not a lot different form modern Asian elephants – with a few adaptations such as size, hairiness, smaller ears and short tails etc. In other words, mammoths should have had a diet similar to modern Asian elephants – but it is assumed by mainstream they lived in the tundra.