To add to that, most of their structures in the Amazon would have undoubtedly been built by wood (plentiful) rather than stone (scarce).
Also, I think 30 years of a field being abandoned in the Amazon is likely more than enough for it to return fully to jungle. It's not like explorers were running around counting tree rings.
Also, I think 30 years of a field being abandoned in the Amazon is likely more than enough for it to return fully to jungle. It's not like explorers were running around counting tree rings.