I keep on seeing this but Mammoth is completely valid because it's not just talking about the extinct animal, it's talking about the concept, "size" - as in, that was a mammoth beating they gave the Avalanche (which is a singular plural.)
And like the Avalanche, fans will say Mammoths as they say Avalanches. It's not a big deal.
My actual dislike is how hard they're sticking with Utah as the place name. I honestly think Salt Lake _____________ rolls off the tongue better in most cases than Utah _____________.