Heading west in UT means getting away from the crowds. Someone already mentioned Great Basin NP. Nice cave tour there. A drive up to Wheeler CG and trailhead is great on the hottest days of the year, as it is still pleasant up there. There's a hike from the top that takes you through a bristlecone forest. They have markers near some of the trees saying how old they are and what was happening in human history when they started growing. Really interesting. On the way there, if you take UT 21, you'll go by the ghost town of Frisco. Some interesting buildings. Disconnect from the 5'er and explore for an hour or two.
Ely NV sits around 6500' so is cooler than the valley floors. Lots of mining history there, plus the Northern NV RR. Never ridden it though. There are charcoal ovens near Ward. We stay at Cave Lake SP. No hookups, but there are showers and flush toilets and a dump station. Around 7000' elevation so it usually cools off nicely at night.
Of course there's Cathedral Gorge SP, although with all your time in UT, you might get enough of red rock territory.
Back in UT, there are several of really nice scenic drives around mid-state. Nebo Loop is on the backside of Mt. Nebo (surprise!). Alpine Loop is on the backside of Mt. Timpanogos. There's also Skyline Drive that goes along a ridge for quite some distance. None of these are roads to tow on, but nice day trips.
Have you ever spent any time in the western Uintas? Many have seen the eastern end north of Vernal near Flaming Gorge, but the Mirror Lake Scenic Byway is quite gorgeous.
All of these scenic drives have great wildflower displays in mid Summer, elevation dependent.
Maybe stay around Heber rather than dealing with the SLC valley. You can do many of these scenic drives from a central location in the Heber area. You could also take a day trip to Mt. Timpanogos Cave NM, although there's a 1000' climb in 1 1/2 miles on a paved trail to get to the entrance.
Have you investigated Nine Mile Canyon. Lots of petroglyphs and other ancient rock art. Worth a day trip. Do a search on Nine Mile Canyon and restrict your search to PDF files to find several guides to the area.
You do plan in advance. I'm still finishing up our planning and we're leaving in four days!
Have a great trip to Colorado this year.
Ken & Allison
2 Camping Cats (1 diabetic)
1996 4Runner, TRD Supercharger, Edelbrock headers
2007 Fleetwood Arcadia, Honda EU2000i
4 mountain bikes, 1 canoe, 4 tents, 8 sleeping bags, 2 backpacks
(You get the idea!)