Question
I just notice a dug out area under a very large oak tree, when I reach in it seems hollow pretty far up.. what kind of animal could be digging from the bottom up??It is a pretty large hole and needless to say I am FREAKING out.. Thatnk you for your help..PLEASE let me know asap...!

Answer
I am not sure it was an animal that dug it out. Oaks are notorious for hollow spots usually due to insects, which then an animal might have gone after. Without significantly more details I can't be much more help. I would suggest,
first NEVER put your hand in a hole blindly!!
SEcond, visit http://icwdm.org and there are resources there to help you narrow the possibilities assuming it is an animal (which is not at all certain)

Once you have significantly more data then you can contact me again at the website.