A controversial 8-foot fence erected by a billionaire ranch owner on long stretches of his property’s perimeter is harming wildlife and degrading habitat across a vast valley in southern Colorado, according to a report by wildlife experts made public this month.
— one chosen by the ranch’s managers and one by Costilla County leaders — found that the extensive sections of fence were threatening wildlife by blocking their movement to food, water and safe habitat.
The 83,368-acre in the San Luis Valley provides significant habitat for wildlife like elk and mule deer, according to the report. The ranch also may be home to threatened or endangered species, including Canada lynx, American marten, snowshoe hare and Gunnison’s prairie dog. About a third of the ranch is protected under a conservation easement for elk habitat.
“Elk, mule deer, and wildlife species need to access different areas of (Cielo Vista Ranch) and beyond to get to various resources and escape from threats such as deep snow during winter and hunting pressures,” the report says. “The existing high fence can restrict wildlife movement along migration corridors, between seasonal use areas, and during daily movement to the point that it threatens the survival of individuals and the associated populations.”
The report is the most recent evolution of a yearslong dispute over the fence pitting the local community and county government against the ranch’s owner, William Harrison. Harrison, heir to a Texas oil fortune, began constructing the fence in 2021, prompting outcry from locals about erosion and water problems created by the construction. They also expressed concern about the fence’s impact on wildlife populations.
Harrison said the fence was necessary to keep his small bison herd on the ranch and to keep out trespassers. Hundreds of local residents are allowed legal access to the ranch — known locally as La Sierra — for grazing and collecting firewood through rights granted to their families before Colorado became a state. Those rights-holders have said the fence is intended to intimidate them or restrict their access, but Harrison’s attorneys have said the fence is meant to ward off those without access rights.
The ranch also encompasses Culebra Peak — one of the state’s 58 mountains that reach more than 14,000 feet in elevation — and to hike to the summit.
Since construction began, the fence controversy has spurred litigation, a state-led water quality investigation, a new state law and rewritten county regulations banning large fences. Harrison stopped building the fence in 2023 after a judge ordered a halt to the project, but more than 26 miles of completed fence sections still line the ranch boundaries. Some sections of the fence span more than three miles and are located at elevations higher than 10,000 feet.
A 2024 mandated the wildlife impact study. Ranch management contracted with Durango-based ERO Resources Corporation and county leaders chose the Wildlife Connectivity Institute of Gallatin Gateway, Montana, to complete the work.
The 83-page study documents which species may live near the fence, how the fence impacts its surroundings and the wildlife, and how the ranch could make the fence more friendly to wildlife.
County officials and Harrison have not agreed on how to implement the report’s recommended changes to the fence, court filings show. A document filed last month by Harrison’s attorneys states that, after months of negotiation, the two sides could not reach agreement by the court-mandated deadline of May 15.
The judge in the case on June 3 sent the case back to the Costilla County Board of Adjustment for further proceedings to determine how much of the fence is subject to new county rules regulating high fences.
Attorneys for Harrison did not respond to questions from The Denver Post about whether the ranch planned to implement any of the recommended changes before this story’s deadline.
At a Costilla County commission meeting on June 16 — after the county — community members called on Harrison to follow the report’s suggestions.
“If Mr. Harrison decides not to follow it, that’s sad, because it’s the right thing to do,” said Joseph Quintana, a lifelong resident of San Luis who has been part of the community group leading the charge against the fence, called La Sierra Environmental Guardian Committee.
The report validates the community’s original concerns about how the fence would impact wildlife, he said. The committee would likely be satisfied, Quintana said, if Harrison would make the recommended changes and agree to abandon plans to build any new fencing.
County attorney Nicolas Sarmiento said during the meeting that ongoing court proceedings limited what he could disclose, but he said there was no ongoing negotiation about the report’s recommended mitigation measures.
The report authors listed hundreds of changes that would make the fence sections more friendly to wildlife, such as lowering the fence in places so animals could jump over it, raising the bottom of the fence so that small animals could pass through, and removing barbed wire from the top and bottom of the fence.
In some areas deemed highly important for wildlife, the authors recommended removing the fence entirely.
The fence, as constructed, is more than 8 feet tall and is topped with a strand of barbed wire — too high for many animals to jump and dangerous for those that attempt to do so. The wire grid that makes up the fence reaches to the ground, where it narrows to openings 3 inches tall. That’s too tight for many animals like turkeys, coyotes and bobcats to crawl through.
Fences that block wildlife movement keep animals from reaching water and food as the seasons change the landscape, according to the wildlife report. Animals must move as water sources dry out in the summer and snow blankets the forage they seek at higher elevations. When animals’ movement is blocked, it requires them to use more energy to meet their needs and keeps migratory species from their traditional routes.
“Animals can also die along fence lines, becoming too weak to find alternative routes to suitable habitat, water, and shelter,” the report says.
In the spring, when animals’ energy stores are low, navigating uncrossable fences can cause pregnant wildlife to miscarry and, over time, result in declining birthrates, the authors wrote. Fences can also obstruct animals’ escape routes during a wildfire.
And collisions with a fence that has small openings can cause injury or death for ground birds and low-flying birds like grouse and raptors.
Even fences with “wildlife jumps” — sections where the top section is lower so animals can leap over — can cause problems if the jump isn’t low enough for calves and fawns to clear. It might still separate them from their mothers and herds or entangle them in the fence.
The ranch installed 29 wildlife jumps across the 26 miles of completed fence sections and planned to install more before a judge’s order stopped all construction on the fence.
The report’s authors recommend modifying the fence sections so that there is a large animal jump at least every 1,000 feet, along with ground openings for small mammals every 500 feet.
“Wildlife-friendlier fences should allow wild animals to jump over and crawl under or through easily without injury,” the report says.
