Search efforts were increased Monday afternoon after no trace was found near Dollar Lake of a man and three children lost in the Weminuche Wilderness.

There are about 25 personnel searching for the 32-year-old man and his three children in Colorado's largest wilderness area, said Ron Corkish, the head of La Plata County Search and Rescue.

He said the La Plata County Sheriff's Office, Upper Pine Fire Protection District, Flight for Life and the Durango & Silverton Narrow Gauge Railroad are involved. A K-9 unit is also being used.

On Saturday, the Bayfield man and his 8-year-old twins - a boy and girl - and his 6-year-old son parked at the Cave Basin trailhead near Vallecito with the intent of a day hike toward Dollar Lake.

However, the group did not return, and were reported missing to authorities by the man's wife either late Sunday evening or early Monday morning. She described her husband as an experienced camper.

According to the U.S. National Forest Service, the trail the group was traveling is a 4.5 mile trek that increases in elevation from 10,800 feet to 12,360 feet to overlook Dollar Lake, and the larger Emerald Lake below.

The trail starts off wide, the Forest Service's trail map says, but soon disappears, requiring bushwhacking, a compass and a map.

"There are no trees on the trail, but meadows and sinkholes that fill with water, due to the caving in of the limestone," the report says.

According to La Plata County Sheriff's Office spokesman Dan Bender, the man's cellphone last pinged around 6:15 p.m. Saturday near Vallecito. There has been no signal since.

Corkish said multiple interviews with hikers who encountered the group Saturday said they were traveling with light clothing, little gear and no sleeping bags.

"They were not prepared to spend the night," he said.

The National Weather Service in Grand Junction reported overnight lows at that elevation have been in the mid-40s, and will continue to be for the rest of the week.

Corkish said as of 3 p.m. Monday that there were no signs of the group in or around Dollar Lake, and crews are focusing on the many side trails that split from the main trail.

"Its very easy to pick up the wrong one," Bender added.

Corkish said search crews plans to bring in a night vision aircraft should the effort extend into the evening.

Check back at durangoherald.com for updates on this story.