Going backpacking through the Teton Crest Trail next week, and I'm in a pickle over which lens to bring for my A6000 (APS-C): 18-105mm f/4.0 or 12mm f/1.8.

Sony SEL18105G 18-105:
Pro: Versatile focal length, lens stabilization, auto focus.
Con: Heavier, smaller aperture, narrower field of view.

Rokinon 12mm:
Pro: Lighter, wide angle, large aperture, prime lens
Con: No AF, no stabilization, no zoom for potential wildlife shots.

I think I'm mostly interested in landscape shots, but I wonder if I'll miss the versatility of a zoom lens. Bringing both lenses is pretty much out of the question since weight is a pretty big priority while in the backcountry. Thoughts?

Zoom on camera, prime in your pack.

Panoramas are nice, but pics of unique features are more interesting.  Choose your lens according to what you plan to shoot.

For me and my photography (mostly landscapes), I'd take the zoom. The versatility of focal range is important to how I shoot.

I'd take the zoom, but knowing me the wide would be in my pack. Every time I downsize my lens load I end up in a situation where I have the wrong lens. It's Murphy's law of photography, if your only lens is wide you'll come upon a shot that's amazing...but only with a long lens and if your only lens is long you'll find this amazing vista that cries for a wide lens.

You'll wish you brought both.  That and per B&H, the Rokinon 12mm weighs less than 9oz dude.  If you can't carry 2/3 of a can of soda in your pack weight wise right now, you need to cut something else out.  

There's a reason why a lot of us have ended up bring a bag with multiple lenses when we go places.  Too many 'ah, damnit' moments.

If you really only take one (and seriously, how much is another pound going to kill you?) take the zoom. You can always take multiples for a pano shot, but you'll never be able to zoom a 12mm.

What I suggest you do is spend a day locally on photo safari. Spend have shooting only the 12, and half shooting only the zoom. You'll learn a lot.

Even though fixed focal-lenght lenses are way sharper and offer less distortion; but they can be inconvenient to use. Ken Rockwell often says "zoom with your feet," personally it is just a PITA to move your tripod a half-inch or so. I prefer the zoom lenses, many times you can frame the photo exactly with just a flick of the wrist.

If you want perfect non-distortion photos, there is built-in on-camera distortion correction in Nikons, or you can use Photoshop/Lightroom etc.

What about picking up a used 16-50 (4oz) instead of your 18-105 (15oz)? That plus your 12mm ends up being 13oz and you get some extra versatility.