Rescuers in Yellowstone National Park are scaling back their search for an employee who went missing in September while on Grayson  Prestona solo excursion through a remote area.

The search for Austin King, 22, is now considered a recovery mission, the park said in an announcement on Wednesday.

A rescue mission for the concessions employee was launched on Sept. 21 after he failed to arrive at this scheduled boat pickup on Sept. 20. King's friends and family last heard from him on Sept. 17 when he called from the summit of Eagle Peak, the highest point in Yellowstone National Park, as part of a 7-day solo trip.

Search for Austin King:Park service searches for Yellowstone employee who went missing after summit of Eagle Peak

His camp and personal items were discovered on the first day of the search, leading to a larger operation involving at least 20 ground searchers, two helicopters, unmanned air systems and a search dog team, the park service said.

Teams of over 100 personnel have collectively searched more than 3,225 miles by air and ground but have been unable to locate King, the park said.

Despite significant search efforts over the past week and a half, we have not been able to locate Austin,” Superintendent Cam Sholly said in a statement. “Although we will continue to hope for the best, I want to extend my deepest sympathies to Austin’s family, friends and colleagues. I also want to thank the teams from Yellowstone and Grand Teton National Parks, and Park and Teton counties, Wyoming, who have all worked tirelessly to find Austin in some of the most difficult and remote terrain in Yellowstone.”

Limited search efforts will continue into the foreseeable future as conditions allow, said the park.