The devastating spruce beetle infestation in the San Juan Mountains has crossed the Continental Divide, and within the next few years, will spread into the high country around Durango and Silverton, leaving in its wake an expanse of dead trees.

“I tell people all the time: you need to get up there before it starts to look different,” said Kent Grant, a Durango-based district forester with the Colorado State Forest Service. “Already it’s increasingly more obvious. It’s just around the corner.”

The spruce beetle epidemic started in Wolf Creek in the late 1990s, and because of the effects of drought, warmer winters and densely stocked forest stands, the insect’s outbreak rapidly intensified.

Over the past nearly two decades, the spruce beetle tore through more than 120,000 acres of the Weminuche Wilderness, which at 488,210 acres, is Colorado’s largest designated wilderness area.

And recently, the infestation has made its way as close as Vallecito Lake, about 20 miles northeast of Durango, mainly feeding on Englemann spruce trees at higher elevations above 9,000 feet.

But within the past year or so, Mountain Studies Institute’s Anthony Culpepper said the spruce beetle finally found a way to cross the eastern flank of the Continental Divide, near Silverton – a natural barrier that had kept the insect at bay.

“We don’t have definitive science how the beetle was able to cross over because that’s a lot of open alpine terrain with nothing for a beetle to consume,” Culpepper said. “But somehow they did.”

Last summer, field surveys found increased spruce beetle activity had started to kill off tree stands in the high country between Durango and Silverton; popular areas that include Coal Bank Pass, Cunningham Gulch, Yankee Boy Basin and along the Colorado Trail near Stony Pass.

“Now the question is: How rapidly does this spread?” Culpepper said. “But definitely within the next couple of years, places around Silverton, along U.S. Highway 550, you’re going to start to see dead trees.”

It’s too early to speculate how devastating the infestation will be in this portion of the San Juan Mountains, but among forestry experts, Wolf Creek Pass stands as an example of the worst-case scenario.

There, spruce beetles left nearly all mature Engelmann spruce trees dead, a jarring sight for motorists traveling the remote mountain pass. The landscape was further decimated by wildfires in 2013, known as the West Fork Complex.

“Whether it gets as bad as Wolf Creek, I don’t know,” Grant said. “Regardless, the prognosis isn’t great.”

Spruce beetles are native to Colorado, but this recent scourge is generally considered an epidemic worse than normal as the insect takes advantage of the changing climate, Grant said.

“Cold weather can reduce the amount of beetles, but our winters aren’t as cold as they used to be,” Grant said. “And with the drought we’ve had in recent years, those trees aren’t healthy enough to defend themselves.”

In Colorado, the spruce beetle has impacted more than 1.5 million acres over the past two decades, by far the state’s most widespread and damaging insect. The U.S. Forest Service said it will release its annual update report on Monday.

Yet for this portion of the San Juan Mountains, news the spruce beetle crested over the Continental Divide brings closer to home the impact of seeing a landscape turn from green to a pale gray.

“While this will have a big impact on us aesthetically and emotionally, this is a natural piece of our environment, and the next step is figuring out how we shepherd this along,” Culpepper said.

Local, state and federal land managers have generally conceded that combating the spruce beetle is both cost prohibitive and ineffective in preventing the insect’s spread.

Therefore, response efforts turn to protecting valued resources where possible, such as roads, campgrounds and hiking trails and mitigating hazards, such as the highly increased risk of tree fall. In the past, the Forest Service has held timber sales, and informing the public, especially tourists, has become a top priority.

Chris Robbins, spokesman for the Durango & Silverton Narrow Gauge Railroad, said it’s too early to tell whether the infestation will affect tourism on the train, which cuts through the heart of the San Juan Mountains along the Animas River.

“This is definitely something that has been on our radar, and we need to plan for it,” Robbins said.

Mary Jo Coulehan, who’s been executive director of the Pagosa Springs Chamber of Commerce for 10 years, said the sight of a beetle kill forest hasn’t had an impact on tourism in the Wolf Creek area.

“It’s certainly a blight and something people notice as they drive through,” she said. “But that has not affected our tourism numbers or stopped people from getting out into all the different popular hiking spots.”

The spread of the spruce beetle, and the ensuing drastic change of the landscape, is a harsh reality the community must come to terms with, Grant said.

In an open area, it takes about 35 years for a spruce tree to grow just four and a half feet, and that number is closer to 75 years in shaded spots. And as the climate changes, it’s hard to say if spruce trees will recapture the mountainsides.

“It will take centuries before this area ever looks the same,” Grant said. “It’ll all come back some day, but we won’t be around to see it. But that’s nature, and what can you do? We have to live with it.”

jromeo@durangoherald.com