I'll be quick, I work for a shipping company on the east coast of America.
We receive shipments from abroad containing ancient excavated technology, thousands of years old and ship it inland in various unmarked and hidden trailers.

I only hear vague stories of where they come from.
Apparently what we think of as alien tech is actually ancient human tech from a long lost civilization, which we have gone to wars over to obtain.

I hear north america is surprisingly, mostly absent of these caches and it has to due something with where the ice caps were, not sure.