Search teams and volunteers on the ground and in the air scoured a 36-square mile area in the Uinta Mountains Monday looking for a 12-year-old Boy Scout (search).

Garrett Bardsley of Elk Ridge was last seen Friday. Police said he was fishing with his father when he was sent back to camp a few hundred yards away to change his wet shoes.

Summit County Sheriff Dave Edmunds (search) said more than 200 volunteers and search-and-rescue team members combed a four-mile radius over the weekend. They began again about 7:30 a.m. Monday.

Edmunds said the boy's safety was in jeopardy because of near-freezing temperatures and deteriorating weather.

He said searchers' main concern now was that they were looking for someone non-responsive.

Edmunds characterized the chances of finding Garrett alive as "pretty grim."

The fall-like weather in the region has dipped into the low 30s at night, and predictions called for worsening conditions. There were reports Monday of soaking rains in the area.

The boy was wearing light clothing — only a T-shirt, sweats and tennis shoes — and had no provisions with him when he vanished.

No clues have yet turned up as to where Garrett might have gone, but Edmunds said it was easy to see how someone could have gotten disoriented in the thick stretch of forest where the boy vanished.

He was on a three-day scouting trip with his father and others when he disappeared in the mountains, about 50 miles east of Salt Lake City.

Garrett's mother, who was on a cruise, cut her vacation short to help try to find her son.

One woman taking part in the rescue effort told FOX News that searchers were "very emotional" as they combed the area. Volunteers were calling to each other in the woods but hearing nothing except echoes of their own voices.

FOX News' Alicia Acuna and The Associated Press contributed to this report.