Resumen
Fazenda Colorada sits in cattle country east of Rio Branco, Acre, at about 9.876° S, 67.535° W. From the air it is a compound geoglyph: a circle, a square, and a double U-shaped ditch that encloses mounds and joins a trapezoidal enclosure. Ditches are several metres deep and tens to hundreds of metres across. Denise Schaan, Alceu Ranzi, Martti Pärssinen and colleagues mapped and excavated Acre earthworks from the 1990s onward.
Radiocarbon dates from Fazenda Colorada concentrate between about 1925-1081 cal BP (roughly the first millennium CE), with a later visit around 706-572 cal BP. Pottery is sparse. Most researchers treat the ditched shapes as ceremonial gathering grounds rather than towns, though the 2026 lidar debate is precisely about how many people the wider landscape could hold.
In 2026 Pärssinen, Kalliola, Ranzi and others published airborne laser scanning over 4,497 km² of southwest Amazonia in Nature. They reported 396 previously undocumented earthworks in the survey swath and estimated 24,000-30,000 geoglyphs across the Aquiry zone, with a possible peak population on the order of millions. Fazenda Colorada is the named, excavated anchor for that map on this atlas, not a claim that one ranch is a city of three million.
The structures are threatened by pasture conversion. They are not UNESCO-listed. Compare Caral for an earlier Andean urban path and Tiwanaku for a highland state that declined in the same late-first-millennium window the Nature authors mention.