I just watched a documentary on Percy Fawcett "Secrets of the Dead: Lost in the Amazon" released in 2011 and at the end they were speaking of Geoglyphs that had been found due to the logging expansions and google earth, and they posited that they may have been the location of large cities with populations upward of 60,000 or so.
I was wondering if in the past several years any progress had been made of any of the details of the geoglyphs with accuracy or archaeological discovery, or possibly things that were known before the documentary was shot, but were not included.
This is a topic unfortunately covered in a ton of hype and pseudo-archaeology. You've got environmentalists who think the idea of prior ecological manipulation of the Amazon rainforests hurts their cause, an uninformed public entranced by the notion of societies "beyond their times," and nutballs chasing a "Lost City of Z" that's something straight out of Inidana Jones (though if Indy was ever real, his name was Percy Fawcett.) Of the level-headed stuff you're looking for, I can recommend Tulane's William Belee. He's got a few good articles and a book: Cultural Forests of the Amazon : A Historical Ecology of People and Their Landscapes. It's still a rather new field of study, but to summarize: yes, the geoglyps are legit, and studies show human activity's large-scale effects on the ecology. Our prior beliefs made sense because we assumed it was a jungle environment, but they are in the process of being revised as we determine just how much of the jungle has been displaced at some point in the past.