I live in the country with the most UNESCO Heritage Sites in the world - 55. Only two of them were built after 1861 (that is after the unification of Italy) and one of the two is primarily in Switzerland.
The United States have probably the most diverse natural landscape of any nation in the world. They should just stuff the tentative list with natural sites like the Joshua Tree National Park or the Great Salt Lake or even things like the Missouri Rhineland.
I looked at the tentative list of Italy, and you're right -- not one of the proposals is from modern Italy, but there are including a few more natural sites.
The US is adding the natural monuments
1. Big Bend National Park
2. California coast line (this will make NIMBYs upset)
3. Marianas Trench
4. Reefs of American Samoa
5. Okefenokee Swamp
6. Remote Pacific Islands
7. Petrified Forest
8. White Sands
Three of them are in remote Oceania, and three more are in deserts. Okefenokee Swamp is interesting, but if the Everglades are an endangered site, then this one will be another.
Those other sites have too much mining potential or are already used as testing facilities and will not be considered. Just like how the US unlike Europe won't declare usable agricultural lands or prairies as site, either.
That's unfortunate. I literally live beside a UNESCO Heritage Site which is (among other things) usable - and used - agricultural lands (albeit very hilly and difficult).
