Seventy-three miles north of Durango, just south of Ouray, a mountain is falling.

On Jan. 12, an enormous slab of stone, quartzite, according to Colorado Department of Transportation geologists, sheered off the ledge of Ruby Walls above U.S. Highway 550, sending tons of rock down the steep underlying slopes onto the road and beyond, rendering it impassable. Crews have worked to stabilize the mountain side for more than two weeks.

Ty Ortiz, geo-technical program director for CDOT, said the rock feature was the size of a football field.

Unlike a rockfall, where loose rocks and debris roll onto the highway, Ortiz called this a rockslide, and it has been pouring debris.

“This was large failure of the rock mass itself,” he said from Ouray. “And when this mass slid, it was probably pretty well fractured; so when it hit the base of the cliff, it just shattered into thousands of pieces.”

Ortiz said natural erosion and the constant freezing and thawing of water to ice and back within the Ruby Walls is likely the slide’s cause.

“In my experience, it’s the temperature fluctuation,” he said.

After assessing the stability of the remaining debris and working to remove loose materials, steel-mesh panels will be permanently fixed over unstable areas to ensure they don’t go anywhere.

After the slide, CDOT enlisted the help of nearby Heli-Trax, a helicopter-assisted ski operation in Telluride, to get crews to the difficult terrain as soon as possible.

Heli-Trax director of operations Joe Shults said getting personnel on the mountain side was no easy task.

“The landing that we took them to is not the kind you want to do in a helicopter on a regular basis,” he said. “It’s not even a landing.”

Shults spotted for his pilot, Lee Rhodes, who was able to perform what he called a “toe-in landing,” getting only the front portion of the landing skids to touch down on the mountain side, while hovering in place as crews loaded and unloaded themselves and equipment.

In his blog about the project, Rigging for Rescue’s mountain safety and rope access coordinator Mike Gibbs, who was hired to set up ropes to access the slope, called the landing spectacular.

“Rhodes was as steady as a surgeon,” Gibbs wrote in his blog, “setting us down every time just right.”

Rhodes put it simply: “It was very dangerous.”

“It was actually just the one toe,” he said. “We couldn’t fit the other toe on, so it was just my front left skid that was touching rock.”

To add to the nerve-racking scenario, the rock was critically close to the helicopter’s spinning rotors.

“The slope was steep enough that when my one toe was against the rock, the tip of my blade was maybe 4 feet away,” he said. “It’s not something I want to do all the time.”

CDOT incident commander Greg Stacy, responsible for the safety of the undertaking, said, considering the level of risk involved, he would rate his crews “grade A.”

“It’s a pretty massive scale,” he said. “Our crews are all working together well, and everything is going as planned.”

Stacy said all 47 of the 12-foot by 72-foot mesh panels, each weighing 600 pounds, may not be needed to cover about 40,000 square feet, but that eight of the panels will need to be placed directly below the rock walls, and that was another concern.

“When we get those eight in there, then I’ll breathe easier,” Stacy said.

Ortiz said continuing freeze-thaw cycles could be an issue, and that CDOT is taking every persecution to minimize the risk.

“A big concern right now is when we get into those springtime temperatures more often, and then we’ll get wet snows and rain,” he said. “That material is perched right over the road, and it is going to slide, and that’s the big reason the road has been closed.”

Ortiz said CDOT is taking a new kind of holistic approach to such events.

“At individual sites, we’ve done a lot of good,” he said. “But we’re trying to take in the process of not just rock fall, but slide as well. We look at the corridor holistically from a geological hazard point.”

On Sunday, Silverton Mountain owner Aaron Brill and helicopter pilot Phillip Jelinek planned to initiate the final stage of the project: lifting and installing the mesh panels over potentially hazardous areas, where precarious rocks range in size from cobbles to cars.

Stacy called the whole thing a great deal of work: three different crews employed, dozens of personnel up and down the mountain, explosives, rocks whipping down from a thousand feet above, bulldozers clearing the road and helicopters. For Stacy, this is life on Red Mountain Pass. For others, they met with surprise.

“It’s quite the operation,” he said about the scale of the project. “For a lot of our people, this is the biggest and the most unique they’ve ever seen.”

bmathis@durangoherald.com

An earlier version of this story misspelled Greg Stacy’s name.