Authorities on Thursday conducted a massive search in Colorado’s Rocky Mountain National Park for a missing ranger whose last known contact with humanity may have been with a Lawrence man and his two sons.

In searching for the ranger – Jeff Christensen, 31 – officials also were hoping to contact the unidentified Lawrence hikers, one of whom was wearing a sweatshirt with the words “State Track & Field Champions – It’s A Tradition.”

“We would appreciate any help,” said David Eaker, spokesman for the National Park Service.

Christensen was last seen by co-workers the morning of July 29. An experienced mountaineer, he was planning a back country patrol, officials said.

That afternoon, he apparently came across and spoke briefly with a family from Chanute, Kan., near the summit of Mt. Chiquita in the rugged and remote Mummy Range. That family reported there were also two brothers in the area at the time; one from Overland Park, and the other from Lawrence, who had two sons. But there were no other details, officials said.

Anyone who may have been in the Mummy Range on July 29 or 30 and saw Christensen has been asked to contact the park at 970-586-1204. The Mummy Range includes Mts. Chiquita, Chapin, Ypsilon Mountain and Desolation Peaks. There are few designated trails in the area and most hiking occurs cross-country.

On Wednesday, searchers narrowed the search area after hearing a gunshot that could have been in response to several gun shots from rangers and getting reports of smoke.

“That gives us some hope,” Eaker said.

But on Thursday, rainy and cloudy conditions were expected to hamper the search effort, which included ground crews, dog teams, and a helicopter equipped with a device that detects body heat.

Christensen apparently was not planning on camping out, but his backpack did have a variety of gear. He was described as extremely fit, in his fourth season as a ranger, and is an emergency medical technician who has worked ski patrol at Winter Park for the past seven years.