In the area, toxins are embedded in the soil and petroleum is in the groundwater — but no one can say for sure what has caused such widespread illness. Until recently, a now-razed U.S. maintenance building where fuel and herbicides were stored — and where Cota worked — was thought to be the main culprit. But the discovery of a decades-old document with a passing mention of Agent Orange chemicals suggests the government may have been more involved in contaminating the land.

The U.S. Bureau of Indian Affairs was an integral part of everyday life in Owyhee. The agency, which oversaw the maintenance building and irrigation shop, told the U.S. Environmental Protection Agency in February that it found a revelatory document from 1997.

In it, a BIA employee recalled clearing foliage in the irrigation canals at least 20 years earlier, when he sprayed at least one of the herbicides — but possibly both — that make up Agent Orange. The EPA banned one of those chemicals in 1979 because of its cancer risks.

A BIA official told the EPA and tribal leaders that it was long believed the herbicides were used for weed control along certain roads — not the canals — before rediscovering the document.