DENVER (AP) - Authorities braced for the possibility of another landslide in a remote part of western Colorado as they surveyed a massive debris field Tuesday amid dangerously unstable conditions that led them to call off the search for three ranchers missing there.
Mesa County Sheriff Stan Hilkey said the search eventually could resume for Clancy Nichols, 51, who also worked as a county road and bridge employee; his son Danny Nichols, 24; and Wes Hawkins, 46.
But it might not be safe enough to do so until summer.
"We don't want to create any more tragedy than we already have," Hilkey said.
The three men were checking on irrigation problems caused by an initial slide Sunday when a large chunk of a ridge broke off, sending soggy earth spilling like wet cement.
The slide happened in a sparsely populated area. It is 3 miles long, about three-quarters of a mile across at its widest and several hundred feet deep at the center. Even at its edges, the pile is 30 feet deep, Hilkey said.
The slide most likely was triggered by runoff from Grand Mesa - one of the world's largest flat-topped mountains - following two days of strong rain, Hilkey has said.
Jonathan White, a Colorado Geological Survey geologist at the site, told reporters Tuesday another slide seemed inevitable because of a buildup of water in a depression created by the first big slide.
"We're having a significant amount of runoff that's flowing into that depression right now," White said. "That's a big concern.
White said it was impossible to predict when the next slide would occur. It could be years from now, when people have forgotten the danger and no longer are taking precautions, he said.
Mudslides are common in the region, which sits on soft sandstone and layers of weak rock, said state geologist Karen Berry. The area saw a spate of them in the 1980s.
It was the size of Sunday's event that made it unusual.
The sheriff said the slide at one point roared up a hill and then down again.
"The power of the slide itself is enormous," Hilkey said.
For now, little can be done to minimize the risk of another slide. The terrain is too unstable for the work necessary to try to drain the water, geologists said.
Jonathan Godt, a Colorado-based landslide group leader for the U.S. Geological Survey, said the "practical engineering measures for things of this size are pretty limited."
The area about 40 miles east of Grand Junction has a few residents, but energy workers are active in the area, part of Colorado's productive Piceance Basin.
The sheriff's department was contacting people to urge them to be ready for a quick evacuation and to sign up for a cellphone alert system. An automatic landline emergency alert system also is in place. Hilkey said his priorities include ensuring the slide is regularly monitored from the air.
Energy companies have suspended operations in the area, and wells likely will be offline for an extended period, perhaps months, said David Ludlam, executive director of the West Slope Colorado Oil & Gas Association.
White, the geologist, said he did not think drilling played a part in the slide.
Hilkey said he was contacted with offers of help and advice by officials in Washington state, where a March 22 landslide swept a square mile of dirt, sand and silt through a neighborhood in Oso, about an hour northeast of Seattle. That slide leveled homes and killed at least 43 people.
A slow but dramatic landslide occurred in April in the Wyoming resort town of Jackson, damaging a home and forcing evacuations. A massive effort to slow further movement there by dumping over 1 million tons of earth at the foot of the slide appears to have paid off, and nearly all homeowners have returned to the area.
Still, town officials remain worried enough to contemplate long-term solutions that include pinning the ground in place with a system of cables anchored to firmer ground deep within the hillside.
Fires and flooding last year in eastern Colorado have raised concerns about slides there.
Geologist Berry said a different topography in the east made large slides less likely, but noted the region was more populated. She said people in areas where mudslides are possible should watch hillsides for warning signs such as cracks and running, muddy water during and after rains.