Fiendish Plot of Dr. Mahrs (2009)

From publisher burb:

A mad (and not too mentally stable) scientist, Dr. Rom Mahrs, has discovered a device that creates a doorway between the Hollow Earth and the Surface World in southern California. Using the device, he’s moving creatures to his secret lab deep in the Louisiana bayou region.

Dr. Mahrs has always been looked down upon by his peers as something of a “Quack” or “Nutcase.” Still, he was able to get a job with the U.S. Army working on ways to defend against mustard gas attacks, but was fired for actions considered “publicly immoral.” He swore revenge for this insult.