I'm having a few issues with ambient fog or whatever it's called - I keep getting dark shadows and lines outlining structures or protrusions in the wall from a distance.

Here's a screenshot:
http://i.imgur.com/SJ8oN.jpg

But then again, I've seen it on my character's stuff and closer objects too.
Screenshot here:

http://i.imgur.com/TmLRX.jpg
there's that dark spot behind the bow that stays there constantly - and you can tell that the shadow is under the tree branches.

And here: http://i.imgur.com/J2Ccz.jpg
you can see it on the axe, on the character's hand, the boards on the ground, and the wrecked boat in the back.

anyone have an idea of what could be causing it?

Do you have a mod that adds SSAO or do you have any driver tweaks that turn SSAO on?

ha. that was it. turned Ambient Occlusion off using NVIDA control panel. Totally didn't think of that.
Thanks!

You're welcome. You should also notice better performance as SSAO is a moderate performance drain.