Search crews on Sunday were bringing the body of ultra-marathon runner Micah True out from the mountainous New Mexico wilderness where he was found dead after setting off on a 12-mile run, officials said.

The process of recovering his body, which was discovered on Saturday, was slow and grueling due to the terrain in the Gila National Forest, said Tom Bemis, incident commander with the New Mexico State Police.

"They are bringing him out now. It's very rugged territory," Bemis said.

There was no further information as to the cause of True's death, he said. His body was found with no obvious signs of injury, police said.

Officials with the local medical examiner's office accompanied the search crews retrieving True's body, Bemis said.

An autopsy will be conducted, he said.

Headed out for a 12-mile run, True, 58, left the Wilderness Lodge and Hot Springs, four miles from the Gila Cliff Dwellings National Monument, on Tuesday and did not return. He had been carrying a water bottle and was wearing shorts and a t-shirt.

He was missing for four days before searchers found his body in the high-desert wilderness near the Arizona border in southwest New Mexico.

Nicknamed "Caballo Blanco," or White Horse, True became a celebrity after he was featured in the best-selling book "Born to Run" by Christopher McDougall.

True served as race director for the Copper Canyon Ultra Marathon, a roughly 50-mile race that drew a dedicated group of runners to Northern Mexico.