[blam]

"I always think there was a lost civilization that pre-dates the first known civilization, which was very advanced."

You're not alone. This book, Voyages Of The Pyramid Builders, by Dr Robert Schoch, expresses similar views.

As does this one: Eden In The East, by Dr Stephen Oppenheimer.

[djf]

The problem with early civilization type theories though is this. Advanced tech requires specialized materials. That means mining, transportation, and processing. We should find roads, and mines, and slag piles, and processing plants.

It's pretty hard to hide roads, especially the types of roads you need in the mountains where you mine materials.

On the flip side, though, they would have had access to much richer ore bodies than we have today.