Rebecca Rubin, 40, was a member of two underground groups that claimed to act to protect animals and the environment from overdevelopment and exploitation, The Oregonian reported Wednesday.
Rubin had been a fugitive since December 2005. She turned himself in to the FBI at the U.S. border in November.
She has acknowledged her role as an ecoterrorist for the Earth Liberation Front and the Animal Liberation Front, the report said. The organization s struck targets in five states.
Rubin faces a mandatory minimum sentence of five years in prison on arson charges.
Federal authorities believe she became involved with the groups in 1997, when she helped free wild horses from a U.S. Bureau of Land Management corral, then set fire to the facility, causing nearly $500,000 in damage.
Prosecutors say her last fire was set Oct. 15, 2001, when she and others set fire to a BLM corral in Litchfield, Calif. A barn and 250 tons of hay were destroyed.
Two other people charged in the fire bombings, Joseph Mahmoud Dibee and Josephine Sunshine Overaker, are still at large.