[Noxomanus]

I guess they were more or less abondened in the Fourth Age. The Elven Rings weren't there to keep Rivendell and Lothlorien intact anymore and the Elves were leaving. I suppose they took all of their lore and 'paper history' with them as they went. I can only assume Lothlorien turned into a normal forest and came to be inhabited ( or hewn [img]smilies/frown.gif[/img] ) by humans. As for Rivendell,it might have turned into a place humans took residence too. Perhaps it just fell into ruins that became part of the landscape,overgrown by plants and layered with earth.