A decade ago, the Colombian region of Putumayo was the main production center for coca, the raw material for cocaine.
And the guerrillas from the Revolutionary Armed Forces of Colombia (Farc) were well placed to profit from the illegal drugs trade.
Today, there are still small fields of bright green coca cut from the virgin jungle, but the rebels have found a more lucrative, and far safer, source of income: gold.
It was here the US military aid package, known as Plan Colombia, which has amounted to some $8bn (£5bn) since 1999, was concentrated.
Since 2000, fleets of spray planes have dropped glyphosate chemicals over the coca bushes, managing to reduce, but never eradicate, drug production.
What the chemicals have done is push local farmers into the new, informal industry of gold mining.
"We estimate that the Farc here make 800m pesos ($450,000) a week from illegal gold mining," said Jhimmy Calvache, the acting mayor of Mocoa in Putumayo province.
Colombia has vast gold deposits, especially along the rivers that wash down from the Andes Mountains.
It was gold that drew the Spanish conquistadors here in the 16th Century, and now, with prices high for precious metal, gold fever has returned.
Mechanical diggers operate along the riverbeds and banks in Putumayo, protected by heavily armed rebels who allow no access to the sites and impose huge "taxes" on production.
In March, police sought to send in investigators to find out how much gold was being extracted.
They ran into trigger-happy guerrillas and it was decided that, without massive army support, there was no chance of making any meaningful inquiries. The operation was abandoned. . .View Full Article