RIO BRANCO, Brazil — Edmar Araújo still remembers the awe.
As he cleared trees on his family’s land decades ago near Rio Branco, an outpost in the far western reaches of the Brazilian Amazon, a series of deep earthen avenues carved into the soil came into focus.
“These lines were too perfect not to have been made by man,” said Mr. Araújo, a 62-year-old cattleman. “The only explanation I had was that they must have been trenches for the war against the Bolivians.”






