> -Where can I find something to destroy that pillar in the southeastern part of the mine?

You'll get that from the miner you helped with the stuck leg. he's resting somewhere, and you have to find him.

>
> -Is there anything past that south tunnel at the sandstone caverns that's too small to enter while in a cart?

I don't actually know which tunnel you're talking about, but this question dovetails neatly into the next one.

>
> -Also, how do I get Verna's passcard, or some way to make Verna answer her door?

Remember the trick you used to get into the sandstone caverns in the first place? Use that trick again, only in the sandstone caverns, and you'll find what you seek. Both here, and the answer above.

Hope this helps.

Rift "Boy it's dark in here" Traveler