Lots of people get stuck in the thought that landscape photography is only ultra wide angle photography. While there is a place for a good ultra wide lens it isn’t an absolute must. In fact it cane make distinct objects seem smaller then you want them to appear
So with that said yes there is a very good reason to take the 24-70 if you take the 11-16. Also, as has already been said, you may also want to bring your 70-300.
If I had to pick on camera I’d do with the 6D with the 24-70 and 70-300. But I normally don’t shoot wider then 24mm. But if I didn’t have to pick I’d bring both and have the 11-16 glued to the 7d fo any times I might want wider then 24mm.
Photography in Zion (no s 
) can be challenging just due to the cliff walls and the shadows they can cause. Very bright highlights and very dark shadows are the name of the game most of the day.
Check out Canyon overlook espically at sunset. The trail is about half a mile one way but it isn’t too difficult. The view from weeping rock is nice and it’s a short easy walk up a paved path. Riverside walk takes you to the start of The Narrows and is worth a walk even if you don’t plan on heading into the narrows.
Those are just a couple trails but there are plenty more with good views. Hell the view behind the visitor center is great and it just requires you to go onto the visitor center patio.
A couple other things I’d suggest:
1. Get to the park early, and come back late. During the afternoon there are just hordes of people, plus the light isn’t great
2. Rent or bring a bike. Put the bike on the front of the bus and get dropped off at the last stop in the park (temple of sinawava). Then just take your time and ride back to the visitor center. The busses only run about every 15 minutes that time of year so you’ll have the road to yourself. The views on the ride are amazing (far better then they seem while you’re on the bus.
