Coming back to this after looking at some of my old Zion shots... Honestly, id be a bit careful with those two specific choices if youre trying to stay under $900. I remember my first big trip there, I lugged a massive f/2.8 zoom around and my neck was absolutely killing me by noon. Plus, Zion is super dusty and the Narrows is literally a slippery river walk. One thing you might want to consider is the hidden cost of filters. Both the Sigma 14-24mm f/2.8 DG HSM Art and the Sigma 20mm f/1.4 DG HSM Art have that big, bulbous front glass. You cant just screw on a normal filter. Youll end up needing a specialized and expensive filter holder system which can easily tack on another $200. That eats your budget pretty quick. If you want to save some cash and weight, I would suggest:

• Hunting for a used Sigma 12-24mm f/4.5-5.6 II DG HSM. Its way lighter for hiking and gets incredibly wide for those tight canyon walls.
• Looking at the Sigma 24mm f/1.4 DG HSM Art. Its lighter than the 20mm and takes standard 77mm screw-on filters.
• Checking out an older Sigma 17-35mm f/2.8-4 EX DG ASP HSM if you want a super budget option that still performs well stopped down. I learned the hard way that pro glass isnt always the best for hiking. Better to have a lighter bag and some extra money for a decent dry bag so you dont ruin your camera in the river... trust me on that one lol. Just make sure to check the weather before heading in.

Just saw this and had to jump in. I ended up getting the Sigma 14-24mm f/2.8 DG HSM Art last year and I have been super satisfied with it. Yeah, its a bit of a brick to carry around Zion, but the versatility in the Narrows is worth every ounce imo. 20mm often feels a bit tight when you are looking up at those massive canyon walls.

• The Sigma 14-24mm f/2.8 DG HSM Art gives you that ultra-wide perspective that makes the scale pop.
• You can usually find it used around $850 which fits your budget perfectly.
• The weather sealing is solid for when things get splashy in the water. Honestly, for landscapes, I am always happy I chose the zoom over the Sigma 20mm f/1.4 DG HSM Art prime. It just works well when you cant move your feet easily in a tight spot... hope you have an awesome trip!

Building on the earlier suggestion about the weight, I totally agree. ZenDrifter is spot on about the neck pain. I took a heavy Sigma prime on a trail last year and honestly it was kind of a letdown. It was way bulkier than I anticipated and basically felt like a brick after the first mile. I was pretty disappointed because it didnt feel nearly as balanced as the Tamron gear Ive used in the past. Not as good as I expected for a long day out...

Can vouch for this

This ^