Three people were missing Monday afternoon after a massive, miles-wide mudslide swept down a mountain in rural western Colorado.
The three unidentified men went missing Sunday after going into the uninhabited slide area on Grand Mesa to check on local farms' source of irrigation water near the West Salt Creek, officials said.
Mesa County Sheriff Stan Hilkey expressed hope Monday that the three might still be found, but noted that much of the "massive" slide area -- about four miles long and two miles wide -- had continued to shift so much that it was unsafe to send in ground searchers.
“We don’t want to create any more of a tragedy than this already is," Hilkey said at a televised news conference on Monday, adding of the missing men, “We hope they may be stranded somewhere in such a way that they’ve avoided it."
The mudslide Sunday began on U.S. Forest Service property after two days of rain. Part of a mountain broke free and brought a wall of snow, rocks and smashed timber down into an area of rural private property that was inaccessible to the general public.
"The slide came down with so much force and velocity that it came to a hill and came up and over a hill and came back down -- a significant hill," Hilkey said, adding that the slide could be up to 200 feet deep in certain areas.
A "sheer wall" remains where the mountain broke away, and further slides are possible, warned the sheriff, who blamed recent rains for the slide.
"There's no doubt the slide is tied to the amount of runoff and the rain we got yesterday. That seems very logical to us," Hilkey said.
National Weather Service meteorologist Tom Renwick said the area had received 0.3 to 0.7 of an inch of rain Saturday and 0.4 to 0.5 of an inch of rain Sunday -- somewhat normal totals for storms in the area.
"When you add them up, that's not really impressive," Renwick said of the rainfall, at most totaling 1.2 inches over two days. But the closest sensor was nine miles from the slide, he said, so the affected area might have been hit harder.
The size of the Colorado slide, roughly eight square miles, dwarfs the landslide in Snohomish County, Wash., in March that killed at least 41 people when part of a hillside broke away and swept into a subdivision, covering about one square mile.
The slides are not comparable in terms of human loss: In Colorado, no structures have been reported lost and no evacuations have been necessary.
Hilkey said he had spoken with officials in the Snohomish County Sheriff's Office on Sunday morning and got advice on how to handle the initial stages of the slide search.
"That call was very valuable to us," Hilkey said. But he added that the Snohomish slide was measured in terms of feet, and "this one we're measuring in miles, and half-mile increments, and the depth of it is overwhelming."
Hilkey said the upper two-thirds of the slide remains unstable, leaving much of the search work to drones that use infrared sensors to search for survivors. Helicopter surveys were to be conducted later in the day, with a hydrologist and a geologist studying the stability of the slide area.