Search efforts for a Minnesota man who was last heard from in July have been suspended after 20 days as authorities say that his “most optimistic survival odds have run out.”

Grant Gardner had planned on a three-day hike “through the Misty Moon Lake area, eventually summiting Cloud Peak,” according to a statement from Big Horn County Sheriff’s Office in Wyoming. He was last heard from when he contacted his wife on July 29 saying he had made it to the summit, but “since that time there has not been any contact with Gardner,” officials said.

On Wednesday, after a 20-day search, authorities announced that they have suspended search and rescue operations for Gardner in consultation with his family members.

“During the past 20 days, Big Horn County and Wyoming SAR personnel have been searching diligently for Mr. Grant Gardner of Minnesota,” Big Horn County Sheriff Ken Blackburn said in his statement. “In consultation with family members, I have made the heartbreaking and difficult decision to suspend active search and rescue operations for Mr. Gardner. Our teams have exhausted all resources and personnel over the last 20 days. With weather conditions and other factors updated in our search models, we have to face the reality that the most optimistic survival odds have run out.”

Officials discovered Gardner’s vehicle earlier this month in the parking lot of the West Ten Sleep trailhead — where he began his journey — and also learned via the hiking log at the trailhead that he had entered the area “as he had indicated in his hiking plan,” officials said.

Phone records also revealed that he had reached the summit at Cloud Peak — which is around 13,000 feet — at approximately 7 p.m., which was concerning to officials due to the “lack of visible trails through cliffs, timber line, boulder fields and other hazards that had to be navigated after dark before reaching clear trails and safe terrain,” officials said.

“Our teams will rest, then begin search and recovery efforts as time and evidence allow. Many citizen volunteers and outdoors people are continuing to search for clues in an effort to bring peace to this family,” Blackburn said. “On behalf of the family, they want to personally thank each and every one of you who have offered time, resources, and prayers on their behalf. While grieving, they are humbled, and grateful beyond words.”

Officials said they have extensively searched for Gardner using helicopters, planes, foot teams and canines, but “conditions are extremely challenging,” with at least two rescuers suffering from “medical conditions” and needing treatment.

Bighorn National Forest is over 1 million acres, with 191,000 acres dedicated to the Cloud Peak Wilderness area, which is where Gardner is believed to have been traveling, according to the U.S. Forest Service.

“Many team members feel like they have lost a battle by not finding Grant at this time, however, it was not for a lack of effort on anyone’s part,” Blackburn said. “We hope clues will surface that will help bring a final closure to this tragedy in due time.”

ABC News’ Megan Forrester and Tristan Maglunog contributed to this report.