The agency said there is no indication the hunter was involved with illegal marijuana cultivation, which a local fire chief had speculated as the possible cause of the blaze.
No arrests have been made, and the hunter's name was being withheld pending further investigation, according to the Forest Service.
A Forest Service statement Thursday gave no details on how the illegal fire in a remote canyon of the Stanislaus National Forest had escaped the hunter's control on Aug. 17. Because of high fire danger across the region, the Forest Service had banned fires outside of developed camping areas more than a week before the fire started.
"We're not going to release any more information while the investigation is ongoing," said Ray Mooney, a spokesman for the U.S. Forest Service.
Investigators would not say whether the hunter had turned himself in, Mooney said. When the investigation is complete, the U.S. Department of Justice would decide whether to seek restitution.
The Rim Fire has burned nearly 371 square miles -- one of the largest wildfires in California history and has cost $81 million to fight.
In some cases people who have started wildfires in California have been sued to pay for the costs and damages.
The Tuolumne County District Attorney's Office also assisted in the investigation, but declined to comment.
Officials said 111 structures, including 11 homes, have been destroyed. Thousands of firefighters were called in to battle the blaze, which at one point threatened more than 4,000 structures,
The blaze is now 80 percent contained.
Chief Todd McNeal of the Twain Harte Fire Department told a community group recently that there was no lightning in the area, so the fire must have been caused by humans. He said he suspected it might have caused by an illicit marijuana growing operation.
California's largest fire on record, a 2003 blaze in the Cleveland National Forest east of San Diego, was sparked by a novice deer hunter who became lost and set a signal fire in hope of being rescued.
Sergio Martinez was sentenced to six months in a work-furlough program, 960 hours of community service and five years of probation in 2005.
The so-called Cedar Fire burned nearly 430 square miles, caused 15 deaths and destroyed more than 2,200 homes.
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