Rebecca Rubin, 40, was a member of two underground groups that claimed to act to protect animals and the environment from overdevelopment and exploitation.
She had been a fugitive since December 2005 but turned herself in to the FBI at the U.S. border in November.
She acknowledged her role as an ecoterrorist for the Earth Liberation Front and the Animal Liberation Front, and agreed to a plea deal in which she would tell the government everything she could remember about her crimes in exchange for at least five years in prison, but no more than 7 1/2 years, The (Portland) Oregonian reported Thursday.
She refused, however, to provide any names of other participants in the organizations.
Federal authorities say Rubin 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 burned 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.
Chief U.S. District Judge Anne Aiken scheduled Rubin's sentencing for Jan. 27, the newspaper said.
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