I can't remember the name of an 80's movie that I used to watch all the time. The details are VERY vague but maybe someone can help. I remember a mammoth or mastadon like creature, sparkiling waterfalls, and possibly dinosaurs. It took place in a very beautiful land and there was some sort of rock cave! Sounds crazy I know, but It's killing me that I can't remember! Anything helps!

Could it possibly be "The Neverending Story"?

I don't remember any mastodon like creatures in Never Ending Story...

Dark Crystal had dinosaur/mastadon creatures as the mystics in it... and then there were skeksis who were dinosaur/bird like... of course this wasn't animated it was "muppet like" creatures... Jim Henson...

The Dark Crystal (1982)
The Dark Crystal - Wikipedia, the free encyclopedia

Also - there eis the original land before time...

The Land Before Time (1988)
The Land Before Time - Wikipedia, the free encyclopedia