Hi! Good to meet a fellow Desert Southwest mapper!
First off, be careful with natural=scree. That’s specifically for broken, angular rockfall from adjacent rock faces. Most of the loose rock in our deserts is unconsolidated alluvium. That is, rock that has been eroded and transported by water (or wind sometimes). Definitely use natural=scree where it fits, but consider natural=sand/gravel/cobble/boulders (from Grain size - Wikipedia) for bare loose rock or soil from other sources.
All that is for bare surfaces without plant life, though. If the area has plants in our deserts, it’s probably natural=scrub. That covers growth up to small trees, so mesquite, ironwood, acacia, etc. still fit.
Some areas of the Nevada desert could qualify as natural=grassland even though the grasses are rarely green. But if the surface doesn’t have mid-sized scrub or small trees, it could be natural=heath.
Be careful with natural=sand too. There are a lot of old polygons around with this tag and it drives me nuts to go out there and see that the entire area is covered in creosote bush. That’s natural=scrub not natural=sand. It has to be bare sand, like sand dunes, for it to be natural=sand. And if there are actual dunes, you can use landform=dune_system as well.
I’d be careful with natural=desert as well. That tag has some issues. Like, what is a “desert” and where are its boundaries? And, could the area be better mapped using more specific tags?
If you’d like more detail in your desert mapping, consider natural=wadi (proposed) for broad washes or natural=desert_pavement (experimental). And you might look at the Glossary of Landforms for more ideas.