Some dinosaurs were around for millions of years, which is a phenomenal amount of time compared to human history, and if humans go extinct anytime soon we may leave very little trace of our technology for a species 60 million years after us.
Two factors weighed against it: plant diversity and evidence on the moon.
The first comes from the argument that any sufficiently advanced civilization will travel around the globe, so fossil records will show the same plants everywhere. It's tricky to determine this but the evidence seemed against it.
The second is simply that any high technology civilization will eventually travel to the moon, which allows for a much more undisturbed record.
If we didn't already know where the lunar landers touched down, do we really think we'd be able to find them again with just a telescope? That's a lot of area to search.
The BBC actually made a documentary, showing what would happen, if the human race would suddenly vanish from earth: http://www.history.com/shows/life-after-people
There's a short summary on youtube: https://www.youtube.com/watch?v=Rh-lqtxZisA&feature=play...
[EDIT: The movie linked above talks about craters on the moon which are "billions of years" old.]
[Dinosaurs on the moon. What a crazy tought. But certainly interesting ;)]