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For more, see: Cruzeirinho and it's comments, as well as Mustafa, Boca de Acre, and Ranch Parana.
All were reported in "Pre-Columbian geometric earthworks in the upper Purus: a complex society in western Amazonia", by Parssinen, Schaan, and Ranzi, Antiquity 83 (2009): 1084-1095.
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