Rich Moore, 71, and his Jack Russell terrier, Finney, embarked on a climb to Blackhead Peak on August 19 but never made it back home.
His lifeless body was discovered on October 30, with loyal Finney beside him.
Rescuers said it was a “magnificent story of survival”.
Delinda VanneBrightyn, of the volunteer group Taos Search and Rescue, said rescuers carried out an unsuccessful days-long search of the steep western side of the mountain between where Mr Moore’s car was parked and the peak.
Weeks later a hunter found Mr Moore’s body in the San Juan Mountains – about 1.5 miles (2.5km) east of the peak – with Finney still alive but weighing about six pounds, about half her original body weight.
A recovery crew was flown in the next day. Finney was taken to a veterinarian and is now with Mr Moore’s family.
The Associated Press quoted Ms VanneBrightyn as saying that Finney somehow survived, probably by hunting small animals such as mice while also managing to avoid predators like mountain lions, coyotes and bears.
“Jack Russells are pretty fierce, I have to say, they’re tough little dogs,” she said, adding that Finney’s “magnificent story of survival” is a testament to her dedication and loyalty to her owner.
“We are very glad… that Finney was returned to the family because they have lost their loved one, but they still have this wonderful, loyal dog,” Ms VanneBrightyn said.
Archuleta County Coroner Brad Hunt ruled that Mr Moore had died of hypothermia, which can cause people to become disorientated and confused.
From the starting point, the hike to Blackhead Peak gains 2,150ft (650m) in elevation.
Friends of Mr Moore told Outside Magazine that he was an experienced hiker and that he had hiked to Blackhead Peak before with a friend.
Mr Moore’s wife, Dana Holby, told the magazine that Finney was very attached to her husband.
Ms Holby was in Montana visiting her sick sister when Mr Moore told her over the phone that he planned to hike to the peak with Finney, and she told him not to go alone.
She also told the magazine she was shocked to discover that Finney had survived for 10 weeks in the wilderness, and that she and her son wept when they collected the dog from the animal hospital.
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