Colorado officials held out little hope Tuesday for three ranchers who were apparently swept up by a weekend mudslide on Grand Mesa, saying the search had shifted from rescue to recovery.
They also significantly downgraded the estimated size of Sunday morning's mudslide.
Foot searches for the missing men were suspended after officials decided the area was too dangerous and unstable. No trace of them or their vehicles have been found, despite searches by helicopter and drone.
Wes Hawkins, 46, Clancy Nichols, 53, his son, Danny Nichols, 24, had ventured out to see why irrigation water had halted.
"They were in the area doing what ranchers do," Mesa County Sheriff Stan Hilkey told reporters Tuesday. "Water in the West is lifeblood here, and they were investigating why the water had stopped flowing."
What the men probably discovered, officials said, was a smaller mudslide that may have blocked the water's flow Sunday morning. Searchers fear the ranchers were later in the path of a second, larger mudslide.
The slide left a path of devastation now thought to run nearly three miles long and cover 706 acres in an uninhabited stretch of Mesa County in western Colorado. That is a bit more than one square mile. Officials had originally estimated its size at four miles long and two miles wide.
The flow contained mud, timber and stone. It was so huge and powerful that officials likened it to fast-moving liquid ooze as it claimed the ranchers.
"I don't think they had a chance to do anything," Jonathan White, a geologist with the Colorado Geological Survey, told reporters at the Tuesday news conference. "I think they saw this [170 feet high] wall of earth and mud come right at them ... a wall of mud, of rocky debris the consistency of wet concrete. I mean, it's just a force of nature that's kind of unbelievable when you think about it."
Rescuers suspect the missing ranchers may have been pushed out toward the edges of the slide, but the immensity of the devastation has officials and family members worried that their remains may never be found.
"Our worst-case scenario is that we're unable to locate them," Hilkey said. "We would love to bring that kind of closure ... but there is the likelihood we all have to come to grips with that perhaps they won't be."
Tuesday's estimate of the slide makes it about the size of the March landslide in Snohomish County, Wash., that buried a subdivision and killed at least 42 people.
But the Colorado slide appears to be significantly longer and deeper, with some areas thought to be covered by as much as 250 feet of debris. By contrast, the Washington landslide was about 60 feet deep.
The Grand Mesa slide, which started on U.S. Forest Service property and swept onto private land, did not destroy any homes. But it narrowly avoided some industrial gas-production storage tanks that had been filled with water condensate, officials said. The tanks have since been drained.
Colorado's Grand Mesa has a history of failure, at least as long as humans have been around. Stretching back into geologic time, the massive flat-top mountain's edges have crumbled away under assault from water and gravity, tumbling into surrounding valleys and foothills.
That's what officials think happened Sunday, when a massive slice of rock and soil cut away from the northern edge of Grand Mesa after a series of rains.
Officials are worried about the ongoing geological evolution of the area and the likelihood of another slide.
Near the top of the mountainside, a steep cliff face remains where the slide sheared away. A long ridge of partially collapsed terrain has created a new basin where water is collecting.
Officials are monitoring the water and hoping to map the new basin soon in hopes of forecasting another potential disaster. The best-case scenario, officials say, is if the water quickly escapes the new, loosely packed basin and finds a way down the mesa.