When I was a kid, I used to walk along the road and find fossil shells.
We find trilobite fossils that were originally formed hundreds of millions of years ago, many showing tremendous detail.
They have not been crushed and ground into dust. Some will, but some might not.
I know a place a few miles from here where right now I could walk into the gorge and find fossil impressions of maple leafs in sandstone.
As far as cities go, yes, many will fall down eventually. But there is something that would remain, even if they filled up. They would still be excavatable and identifiable.
The sewers.
Seems like half the soil in western New York is tiny fossil shells. There must be something about some naturally occuring forms that lets them stand the test of time, whereas manufactured items crumble to dust. The form of a leaf remains, but the spear made out of the wood is long gone. As soon as we touch something, it is doomed.