Rescuers in Yellowstone National Park searched the area of Eagle Peak on Sunday in an effort to find a park concession worker who failed to check in at the end of a personal trip, authorities said.

Austin King, 22, missed that check-in, at which he was to be picked up by a boat at Yellowstone Lake’s Southeast Arm on Friday following a weeklong trek on and around Eagle Peak, the National Park Service said in a statement.

On Sunday, more than 20 searchers on the ground were aided by two helicopter-based crews, drones and a canine search team in the so-far unsuccessful effort to find the missing man on and around Eagle Peak, the park service said.

On Sept. 16, King spoke to a backcountry ranger at a location not on the route of his planned trek, telling the park official he planned to climb Eagle Peak the next day, which he did, according to a park service missing person flier.

At about 7 p.m. Tuesday, King told a relative about the challenging conditions on Eagle Peak’s summit, according to the flier. The mountain rises 11,358 feet above sea level and is Yellowstone National Park’s highest location, according to the service.

“While on the summit, King described fog, rain, sleet, hail and windy conditions,” it said in the news release.

The Tuesday phone call was the last anyone heard from King, the park service said. It’s not clear what happened between his summit on that day and his failure to show up for a boat on Friday.

Rescuers launched the effort to find King on Saturday, the park service said.

That day, search crews found an encampment and personal items belonging to King in the upper Howell Creek area, according to the service. It’s not clear what became of a 2006 Chevrolet Silverado pickup with Minnesota plates that the park service said is associated with King.

Crews from Yellowstone and Grand Teton national parks, as well as from Park and Teton counties in Wyoming, have participated in the search, the park service said.

The park service said aerial and ground searches have focused on the Yellowstone Lake area, as well as Eagle Peak — both popular sites in the 2.2 million-acre park. 

King embarked on his trek on Sept. 14 after he was dropped off by a boat at Terrace Point on Yellowstone Lake, the park service said in its missing person flier.

The lake is home to a shuttle boat service that “provides backcountry access to select sites on Yellowstone Lake for overnight hiking and camping,” according to Yellowstone National Park Lodges, which manages lodging in the park.

In the last three days, temperatures in Yellowstone National Park have bottomed out in the high 20s and struggled to break the 60-degree mark, according to National Weather Service data.

The park service said King is 6 feet tall, 160 pounds, has hazel eyes and was wearing glasses, a black sweatshirt and gray pants.

Anyone with information about his whereabouts was asked to contact the Yellowstone Interagency Communications Center at 307-344-2643.