(CNN) -- Hope is fading fast for the three men missing after a massive mudslide in western Colorado.
Clancy Nichols, 51, his son, Danny Nichols, 24, and friend Wes Hawkins, 46, vanished Sunday after a ridge collapsed in Mesa County.
"We have suspended search operations with regards to anybody actually on the slide itself because it's still determined to be unsafe," Sheriff Stan Hilkey told reporters Tuesday.
"We are essentially in a recovery effort at this point with our three missing people."
He said authorities will continue to manage air resources to monitor water buildup at the top of the slide. That buildup is what makes them worry about the potential for another major mudslide.
"It's enough that we don't feel comfortable having people on any part of the slide at this point, and so we pulled people off of that, and the only thing we're able to do right now is overflights and take pictures and study those high-resolution pictures," the sheriff said.
Authorities told CNN affiliate KUSA that the three men live in the Collbran-Mesa area, which means they know the terrain well.
"They're probably very outdoorsy, probably very prepared for the severe weather and being stuck in the mountains overnight, and those kinds of things," Heather Benjamin of the Mesa County Sheriff's Office told the affiliate.
The ordeal started Sunday when a small slide affected irrigation in the area.
Bill Nichols, the brother of the elder Nichols, told KUSA that his relatives are volunteer firefighters who joined their friend Hawkins to check on the irrigation canal.
When the three men went to investigate, a second and major mudslide occurred, authorities said. It happened after a day of torrential rains, which made it more ferocious.
"The slide came down with so much force and velocity that it came to a hill and went up and over a hill and then came back down -- a significant hill. So the power behind it was remarkable," Hilkey said.
The scope of the mudslide left authorities awestruck.
"It's an understatement to say that it is massive," the sheriff said. It's estimated to be about 4 miles long, 2 miles wide and about 250 feet deep.
CNN's Ed Payne and Joe Sutton contributed to this report.