re: Potential for a human base there?
I'd bet on it. There is considerable evidence for large underground lava tubes and caves around Mars, which (if stable enough) would make excellent bases.
Easiest method would be to use inflatable pressure quarters inside the caves rather than trying to make the cave pressure-proof. With the rock protecting against radiation, and excessive heat losses, the design of the modules would be simple, similar to the NASA/Bigelow concepts.
Of course, down there where the moisture might be, and shielded from the radiation, you might have to share the space with other things... ;)