Rescue workers searched under rocks, beneath logs and on precipitious slopes at Crater Lake National Park on Wednesday in search of an 8-year-old boy who has spent four nights in snowy and cold conditions after wandering from his father.

Park officials said they had not given up hope that Sammy Boehlke may still be found alive, and were expanding the area of their search.

"We're continuing to search for a live 8-year-old boy, focusing on concealed areas, areas under cover," said Park Service spokesman Rudy Evenson.

The child and his father, Ken Boehlke, were out for a day of hiking on Saturday and were attempting to climb a rock embankment, when the youth went ahead of his father and into the woods, officials said.

The youth has camping experience but no formal training in wilderness survival. He was described as wearing a winter coat, long-sleeved T-shirt, cargo pants and light shoes.

He disappeared in wintry conditions. The park, at 7,000 feet, averages more than 500 inches of snow a year.

Snow fell Sunday and Monday, but the weather improved Tuesday, allowing a helicopter to examine the lake's edge and rappelling crews from Yosemite National Park to work their way down the walls of the caldera that holds the lake.

Temperatures in the area Tuesday night were in the mid to high 20s, Evenson said.

About 145 rescue workers continued the search on Wednesday, focusing on wooded areas and looking "under rocks, logs and in small hiding places," Evenson said.

"We are holding out hope he might be in a place like that, where he might have sheltered for a few days."

Technical crews also continue to search the steep slopes leading from the rim of the caldera down to the water — a drop of 700 to 1,000 feet, Evenson said.

Evenson said it's unlikely the boy would have fallen into the lake because obstacles on the slope would have prevented that.

The boy's parents were heading to the searchers' base camp on Wednesday. Evenson said they are holding up "as well as can be expected."

Officials say Sammy Boehlke showed signs of low-level autism but hadn't been diagnosed with the disorder.

"We're taking that into account," said David Brennan, chief ranger at the park.

The search force has at times swelled to more than 200 people combing an area of about six square miles, or 4,000 acres.

The terrain around the lake varies from nearly flat to gently rolling, with house-size blocks of lava and small precipices scattered about. The woods are lodgepole pines and other conifers.

The caldera was formed by the explosion of a Cascades Range volcano about 7,000 years ago.

Brennan said officials were treating the situation as that of a missing person.

"There's absolutely nothing to indicate foul play or criminal activity," he said.