Thanks for the suggestions!
We considered the Valley of Fire, but we could have only stayed there for a couple of hours and thus decided to postpone it for our next trip. The same holds for Death Valley, that we scratched from the to-do list very early because of the time we were spending in the US (in only two weeks, it is just impossible to do everything). But again, Death Valley is very high on our list of places to visit! Maybe in a potential future trip where we will include California as well.
I have never heard about Red Rock Canyon and Mono County. Thanks for these suggestions! Happy to have learned something today ^^