Okay here are my contributions to whether this is a fake or not... I know basic photoshop and i know that this would NOT NOT NOT be an easy photoshop, and something this small would make it almost impossible to clean up lines and make pixels look perfect. There is almost no sign of that "photoshopped" touch often attributed to bad lighting (this lighting seems perfect) What i DO know though, is elephants... I love to study zoology and i can definitely say that this not a living species of elephant (Loxodonta cyclotis, Loxodonta africana, Elephas maximus) I also started looking up some mastodon facts and this thing has got TONS of credit going for where it was found (a perfect environmental match to its predicted lifestyle), and it has staggering anotomical accuracy.

Firstly, this is NOT A BEARS BODY just take alook for yourself, none of the proportions match up, infact none of the proportions are even CLOSE -- and the waking and splashing looks BIG like it was caused by a huge animal.

Its definitely NOT an asiatic elephant, NONE of the features (save for small ears) of asian elephants are present on this animal and the skeletal proportions don't match up at all - high double domed head is absent, as well as the highly arched back... plus the tusks point forward not downward.

African elephant skeleton looks closer, but it definitely does not match. Also, african elephants have a very deep dip in their back and this creature only appears to have a slight dip (which may be an illusion due to the small shoulder hump of muscle mass that mastodons had on their necks). Also the african elephants body looks taller than it is long, and this is not so for the mastodon

With a mastodon skeleton overlayed on top of the image you can definitely see that this has GOT to be what this animal is.
As far as photoshopping goes, I see no apparant give aways that are associated with photoshop. The biggest one being lighting, and repetition of certain elements that do not repeat (water for example... and this image has 2 clearly different splashes indicating 2 different moments in time)
Im unsure about the story still but these pictures are pretty damn convincing, I don't think its EXACTLY the same as the wikipedia rendering, i just think that the wikipedia rendering is a damn good illustration of a mastodon, and therefore if this photograph (of a real mastodon) is genuine, than it just goes to show u that modern scientists predict well. OR maybe they know something that we don't.... The biggest holes with the story were "shouldn't this be the find of the century?". Maybe, or maybe scientists already KNOW about it, as well as Denali park rangers, and for the sake of the species survival it ISN'T MENTIONED.... this sort of thing is seen on Tasmania to this day, where it is estimated that thousands of people have seen thylacines but they refuse to talk about it for the sake of the preservation of the last remaining species. I still can't say this is a fake, sorry.