Bighorn sheep are literally engraved into Utah’s desert landscapes, but they have long been a rare sight in the flesh.

No animal is more commonly depicted in ancient rock art than this charismatic creature famous for its curled horns and the males’ propensity to wander and knock heads. But wild sheep, both Rocky Mountain bighorns in the north and desert bighorns in the south, all but disappeared from Utah following European settlement, thanks to overhunting and exposure to diseases carried by domestic livestock.

Utah wildlife officials have been trying to reverse that bleak trend since 1973 when they released 12 desert bighorn sheep in Zion National Park, the first of numerous re-introductions around the state. For decades the Zion herd languished, but since 2008 it has boomed to more than 800 animals, most of which inhabit the park’s canyons and plateaus.

“We have a healthy sheep herd, which is great, but that means they are at a higher density and they are spreading out. With that comes increased of risk of contact with domestic sheep,” said Cassity Bromley, Zion’s chief of resources and research.

Franciso Kjolseth | Tribune File Photo A group of desert bighorn sheep near the Checkerboard Mesa in Zion National Park hang out near the road. The Utah Division of Wildlife Resources is holding a free bighorn sheep viewing event Dec. 6, 2014, starting at 8 a.m. in Green River.

While this herd is among the West’s strongest, wildlife biologists now regard its size as a threat to its survival because bighorn’s domestic cousins carry pathogens the cause pneumonia and other lethal diseases. Such an exposure could ricochet through wild populations and trigger a catastrophic die-off.

This is the scenario the National Park Service and state officials hope to avoid through a multi-year relocation program set to begin next month after more than three years of study.

In next few weeks, state wildlife workers will capture 50 Zion sheep, mostly females, fit them with radio collars and release them in San Juan County, according to Rusty Robinson, Utah Division of Wildlife Resources big game coordinator.

Another potential solution would be to hunt “excess” sheep, but hunting is not allowed in national parks. Today, the chance to hunt a bighorn sheep is Utah’s most coveted tag, a once-in-a-lifetime opportunity awarded to only 1 in about 283 applicants in 2012. Last year, hunters harvested 82 bighorn sheep.

Moving sheep across the state accomplishes two goals: minimizing the chance of interactions with domestic sheep and bolstering wild herds elsewhere.

The animals are to augment Utah’s most imperiled bighorn herd, which inhabits a unit called San Juan North located west of the Abajo Mountains in Bears Ears National Monument and the Needles district of Canyonlands National Park. Interestingly, this is Utah’s only desert bighorn population that was never wiped out, Robinson said, and once numbered in the hundreds. But in recent years this herd has barely hung on with less than 30 individuals, and sheep populations need 125 sheep to remain genetically viable.

Robinson believes disease has kept a lid on the San Juan sheep.

“With so few sheep in the herd, our tools for managing for sick sheep are limited,” he said. “The plan is to remove the contagious ones and put healthy sheep on top of the others... We have to do something or we will lose that herd.”

DWR has contracted with a helicopter firm to locate the animals, then shoot nets on them from the air. Because the capture is occurring in designated wilderness, the operation was subject of a careful environmental analysis. Crews will take blood samples to test for disease and fit captured sheep with radio collars before they are released in San Juan County. This will take place Dec. 11 and 12 if the weather cooperates.

After four decades of aggressive efforts to reintroduce herds and augment existing ones, about 4,200 wild sheep now roam the state, according to DWR’s sheep management plan.

Rocky Mountain bighorns occupy the Book Cliffs, and Wasatch, Uinta and Deep Creek mountains, while desert bighorns occupy Zion, Kaiparowits Plateau, Glen Canyon, San Rafael Swell, Henry Mountains and Canyonlands.

Yet Rocky Mountain sheep, whose numbers have more than quadrupled since 1996, have fared far better than desert populations. Were it not for the success of the Zion herd, desert bighorn overall numbers would actually be sliding.

Research is a key component of the Zion project, which is being funded with private money, including a $50,000 grant from Zion Forever’s adopt-a-sheep program. The park is also rigging radio collars on 30 sheep that will remain in Zion.

The collars transmit a location ever two hours, giving research a fine-grain look at the animals’ movements.

“It will be a small sample size but it will give insights into causes of mortality. Is it mountain lions? Is it roadkill? It will be anecdotal but we can gain insight into lamb survival,” Bromley said.