Wow, that's the first time I've ever seen anything like that. Have you tried checking to see if that bug occurs without the grass mod?

Other than that the only things I can think of that might cause something like this are video card issues or a problem with the BSA file.

Edit: I had a similar problem with the grass in KOTOR II on a specific planet. Turns out the problem was rooted in my ATI card.

I had the URWLified version but I don't remember it altering the landscape at all. Are you by any chance using a R9 card, I heard of problems similar to this in BF4 with that series.

What's happening appears to be some kind of GPU problem unless the BSA for the textures is corrupted but I'm not sure if that's even possible.

The fact that the problem is isolated to one area though makes the possibility of it being a driver problem unlikely.

Putting in a mod that alters the textures that appear missing might be worth a shot. If that problem still occurs after that then the possibility of the default textures being corrupt/missing is at least eliminated.

This is the first time I've seen a texture glitch like that. The flickering between nearby textures is normal if it's missing the texture, but the squares with normal map are not.

If you haven't already, I'd use Steam to verify your game cache. If something is borked in a BSA, that'll fix it. Failing that, completely deactivate your grass mod using whatever mod manager you use - there's always the possibility of a corrupted texture file included in the pack not playing nice.

I'm sorry I couldn't be of any help.   

In all my years of playing Fallout, I've never came across anything like that before. So I have little knowledge on problems like that.

At least it's limited to Jacobstown though, and not the entire wasteland.

Even if you don't have a land texture replacer, it really seems from the pictures that something replaces vanilla textures with a missing file... in the first pictures, aren't these normal maps?

hard to check it, I mean what exactly is the texture, there are many all mixed. Anyway the snow textures are under texture\landscape\dlcanch, like DLCAnch_snow_RockCanyon01.dds

Do you have the same problem at Quarry Junction?