What did a wooly mammoth eat?

They were or are herbivorous- as are Horses. I once saw what was billed as a living Baby Wooly Mammoth on the back of a not-too-large pickup truck at of all things a Church Flea Market in about l974. It was claimed the creature weighed 225 lbs, same as an average man, and top end for most dogs. I once saw a Bull-Mastiff named Battlewagon that weighed in at about 225.