The 58-year-old True, whose extreme-distance running prowess is detailed in the book “Born to Run,” set out on what—for him—would have been a routine 12-mile run Tuesday from The Wilderness Lodge and Hot Springs, where he was staying. He left his dog at the lodge and never returned. A search began the next day.

Lodge co-owner Dean Bruemmer, who helped with the search Saturday, said he last saw his friend at breakfast. He said True gave no indication of a specific route, which made the search more difficult.

“There are a lot of trailheads up the road,” said Bruemmer, whose lodge is about four miles from the Gila Cliff Dwellings National Monument.

Though daytime temperatures in southwest New Mexico have been mild of late, temperatures dipped into the mid-20s on recent nights. True left for his run wearing shorts and a T-shirt and carrying a water bottle.

Fourteen search teams that were scouring the area Friday were supplemented with additional volunteer teams from across the state Saturday morning, state police spokesman Lt. Robert McDonald said. Teams were hiking and on horseback and ATVs. They also used dogs and employed a helicopter and plane in the search.

Bemis said crews likely would begin removing True’s body by horseback or litter team Saturday night. But he said the body probably wouldn’t make it out of the area until Sunday because of the terrain.

True, who had been friends with Bruemmer and his wife, Jane, for 10 years, would often visit their lodge while traveling between Mexico and his Boulder, Colo., home. As a result, Bruemmer said, True knew the trail system well—which made his disappearance all the more mystifying.

Michael Sandrock, a columnist who writes about running for The Daily Camera newspaper in Boulder, knew True for at least 20 years and had run with him. He called True a pioneer of the sport of ultrarunning, which involves running extreme distances, often on grueling terrain and many miles longer than a traditional 26-mile marathon.