https://www.openstreetmap.org/?mlat=40.799722&mlon=-113.8&zoom=15#map=15/40.7997/-113.8000
In winter a inch of water in summer dry.
Is it already rendered on the default map.
There was a discussion about this on the tagging mailing list in October. I don’t remember whether there was a consensus, but you might get some ideas from the discussion (intermittent vs. seasonal)
I searched further, Salar de Uyuni is a salt_flat http://www.openstreetmap.org/relation/1769713
natural=desert
desert=salt
but using desert is strange
I liked to see it rendered on the default osm map.
I also put it on this site to render.
https://github.com/gravitystorm/openstreetmap-carto/issues/1995