We hit Moab in July and it was hot. We hiked early in the AM and sat in the pool during the day and went back out in the evening. If you are in and out of the car it's not to bad midday (just take it easy). We hiked until about 11:00 AM and it was getting toasty. Be prepared, drink and have lots of water and don't push it and I think all would be ok. Arches is something totally different and worth the stop. Durango is cool but is a mountain town like the other towns you will drive thru in CO. Great Sand Dunes is also worth a stop but if choosing between the two would go to Arches. One thing to note is we rented a condo as we were meeting some family out there. We parked the camper at a campground and let the AC run. It was over 100 out and the camper maintained mid 80's all closed up and shades drawn. If we were in and out It would of bit warmer I think.