Officials say nelson was dropped off for the 25-mile hike into some of Colorado's most challenging terrain. His fiancee was waiting to pick him up five days later, but he never showed up.
Colorado parks and wildlife officials are asking hikers and especially hunters, who tend to go off trails, to look for equipment or possible human remains in that area. They hope to find clues as to Nelson's disappearance and bring his family some closure.
Colorado Parks and Wildlife spokesman Mike Porras said authorities rarely call for outside help, but the hiker's father asked. "This is not a routine practice, but this is not in a place where people usually go," Porras said.
Dan Smith, a volunteer for the Vail Mountain Rescue Group, said Nelson is one of two people missing on the trail. He said Michelle Banek, a mother of four from Denver, disappeared in 2005 and rescuers have long since abandoned the search. He said many people try to go on dangerous hikes on Colorado's mountainous terrain and get into serious trouble.
"This is not Disney World. If you get in trouble, I can't turn off the ride," he said.
The father told wildlife officials that his son was well-prepared for an extended hike.
"He knew what he was doing, and we can only imagine that he had an accident of some kind," Jim Nelson said in a statement.
Friends and family reported that before he left on his trip, he was prepared and followed many of the recommended rules of hiking in the back country. He packed the necessary supplies and he was careful to let several people know where he was planning to hike by mapping his route, which would take him over several of the areas tallest peaks including one of Colorado's most well-known "fourteeners", the rugged Mount of the Holy Cross that stands 14,003 feet tall, located 100 miles west of Denver.
A pair of hikers reported that they had seen a man matching Nelson's description on Oct. 3. Then he vanished.
Trained search and rescue dogs seemed to pick up Nelson's scent off a trail near Lake Constantine on Nelson's planned route, said Smith. But no trace of Nelson was ever located, despite an intense four-day search with helicopters, search and rescue crews and trained dogs.
Porras said there was no indication of foul play.
Rescuers say they are counting on hunters because Colorado's big-game rifle season is just weeks away.
"Hunters head into off-trail areas that most hikers avoid. We're asking that they keep an eye peeled for evidence that could help bring closure to Mr. Nelson's family," Area Wildlife Manager Perry Will said in a statement.
They're asked to look for discarded hiking equipment, an abandoned tent or human remains, and if they find anything, mark the location, take photos and report it.
Porras said hunters have helped solve several high-profile cases. In 2007, a Colorado hunter found the body of an Alzheimer's patient who had been missing for month. The hunter found the remains seven miles from the missing man's home in Cotopaxi.
The Associated Press contributed to this report. All rights reserved.