A lot depends on just how far out of Vegas you're happy to drive. Within very comfortable driving distance (an hour) you have Valley of Fire State Park, Red Red Canyon and Mount Charleston, all of which could work for you. VoF in particular has some amazing scenery. If you want to head a little further afield then Death Valley NP and Zion NP are both possibilities as day trips and either could be just what you're looking for.
If your trip is in summer then be aware that (with the exception of Mt Charleston) these places get extremely hot, Death Valley potentially very dangerously so. Take appropriate precautions.