We were at Bryce Canyon back on May 20, 2012 for the solar eclipse. Bryce is at 8-9,000 ft elevation so temps were comfortable. The next day we drove through Zion to Hurricane UT to restock at the WalMart. Hurricane is at about 3,000 ft elevation and the temperature there exceeded 100 that day. That night we camped at Jacob Lake AZ near the North Rim of the Grand Canyon. Jacob Lake is at 8,000 feet and we had comfortable sleeping temps.
By June 3rd, we had worked our way through Capital Reef, Arches, Canyonlands and then on to Vernal UT with OK temps. Vernal is at about 5,000 feet elevation and the temp on that day exceeded 100 when we visited Dinosaur National Monument.
We plan to go back to UT next Spring, leaving NJ by the 3rd week of April with hopes for cooler temperatures. When things get too hot for us, we will escape to Grand Teton and Yellowstone for much of June.