65 million years ago, a mass extinction event (likely caused by the Chicxulub Meteor) wiped out the dinosaurs, and their remains were hidden from us for millions of years.
Humanity was not around at the time, and there were no major societies or civilizations.
But what if there had been? What if there had been a race or civilization at that exact moment in history, approximately like our own currently, but with an advanced spacefaring device that allowed them all to leave at once, leaving only behind the ruins of their society?
What would be left over from their society, assuming they used similar methods of construction and had similar cities, factories, and historic periods to our own, that we would be able to find in modern times?
To clarify, there would be no fossil records of the actual civilization (all their dead are cremated before departure, and their evacuation is 100% complete, pets included) only the artifacts left behind by their civilization (all habitats, entertainment, and food are provided on their escape vehicles, but everything they had is left behind). And they are not humans, but approximately close enough bipedal creatures that they're very similar to humans.
Assume that they won't be doing anything to impact our world. They could be coming back tomorrow, settled on other worlds, gone forever in a horrible accident, but they can't be having an impact on our world, and we likewise aren't going to find evidence of them from anywhere but here.