Southwest Dave has made some excellent suggestions - the National Parks of Utah are hard to beat.

You might also consider this. On the return trip, take I-80 to Reno. Along the way, the Donner Pass Road which runs from Exit 174 to Exit 194 is a great drive which allows you to get a look at some sections of the railroad through the pass as well as some magnificient scenery.

At Reno, take US 395 south to Nevada 341/342 through Virginia City and then pick up US 50 south of Virginia City which is an old mining town which has reinvented itself as a tourist attraction.

Take US 50 across Nevada and Western Utah and pick up I-70 just south of Salina, UT. I-70 in western Utah is an extremely scenic drive and, unlike so many Interstates has some very good rest areas/observation points. In eastern Utah, I-70 passes only about 30 miles north of Moab and Arches Nat'l Park. Canyonlands Nat'l Park is also just a bit further south. Also in the area, Dead Horse State Park is a great place to visit.

Continue on I-70 in to Colorado and take the loop drive through Colorado Nat'l Monument. This is about a 30 mile loop which takes you back to I-70 in Grand Junction.

Continue on I-70 to through Glenwood Canyon which is perhaps the most scenic section of Interstate in the country and is an amazing feat of engineering. In places, the road literally hangs from the canyon walls.

If time allows, you might leave I-70 and find your way to Rocky Mountain Nat'l Park and Estes Park. However, you would want to check on road conditions before doing so. The recent flooding has played havoc with the roads descending from Estes Park.

Have A Great Trip!!