SOUTH PASS—Corinna Riginos planted her feet among shin-high sagebrush that stretched out of sight. The ecologist, who leads the science team for The Nature Conservancy-Wyoming, was trying to verify if noxious cheatgrass also grew nearby.
Walking along the 7,500-foot-high rolling tableland, not a single blade could be found.
“When we think about ‘defending the core,’ here we are at ground zero,” Riginos said on a still early July morning. “We have this real opportunity to try to keep it that way. Practically speaking, how do we get there?”
“The core” refers to the best sagebrush remaining on Earth. Sagebrush is the backbone of an ecosystem in decline everywhere, including Wyoming. Still, places like South Pass and the Green River Basin are home to, by far, the largest and healthiest sagebrush tracts that are left.
“There’s 16 million acres of core sagebrush area in Wyoming,” Riginos said. “That’s half of what there is across the whole western sagebrush ecosystem.”
Cheatgrass poses perhaps the gravest threat to the shrinking habitat’s long-term persistence. Riginos and fellow TNC scientists Courtney Larson and Charlotte Cadow are embarking on a yearslong mission to get ahead of that threat. They’re trying to find cheatgrass before it takes over.
Where cheatgrass grows in thick, there’s no mistaking it. The landscape’s very color is the telltale sign.
“Cheatgrass has a nice seasonal signature,” Larson said. “It greens up early, then it turns kind of purpley-colored. And then it dies off earlier than other grasses.”
As a result, heavily invaded areas can be easily mapped using satellite imagery.
But predictive models don’t do so well when cheatgrass accounts for less than 15% of the groundcover. The Nature Conservancy crew knows that from experience. In summer 2025, they went to 200 survey plots where they found no cheatgrass. Yet, their modeling predicted 88% of those sites would have some trace amount.
“They overpredict, at low levels of cheatgrass,” Larson said.
One of the crew’s goals is to dial in the predictive models. Verifying what’s growing where takes a whole lot of fieldwork.
“We’re going to try to get 400 random points,” lead sagebrush technician Lauren Marsh said while en route to one of them.
During the 2025 field season, TNC’s techs found the invasive annual species in unlikely corners of Fremont County — deep into the Wind River Range up St. Lawrence Basin and on the high slopes of Green Mountain.
“We’re seeing it at 9,000 feet,” Riginos said. “Someone else saw it at 10,000 feet last year.”
There have even been patches documented along forested, north-facing slopes, she said.
“It’s heartbreaking and mindblowing at the same time,” Riginos said. “The models of habitat suitability don’t really end: 78% of Wyoming is suitable habitat.”
Teton County’s also seeing signs of invasion into landscapes that land managers once thought immune.
“We found cheatgrass at 8,000 feet in the Gros Ventre,” Cadow said.
The Jackson Hole crew has even been observing little patches in the conifers where elk are bedding down, she said, and also where elk manure is especially prevalent.
“In Teton County, we’re really seeing wildlife as a vector,” Cadow said. “Cheatgrass is getting a foothold higher and more remotely than we anticipated.”
Dropping into Sweetwater Canyon during the early-July outing, Riginos, Larson, Marsh and Joey Friedman descended toward several survey plots where they were confident they’d find cheatgrass.
On the steeper, south-facing slopes, it was everywhere. Riginos grabbed a pile of cured, tinder-dry seeds and stems that accumulated atop the soil in the canyon.
“Super good fire starter,” she said. “There’s a reason they call it grassoline.”
One of cheatgrass’ most harmful traits is that it speeds up the wildfire cycle. When an infested area burns, the cheatgrass grows back even thicker. Then the landscape’s even more prone to burn yet again, creating an ecologically devastating feedback loop.
Wildfire-scarred landscapes from the 2024 House Draw Fire and 2025 Red Canyon Fire have become top priorities for keeping cheatgrass from taking over. Funding to pay for the pricey herbicide that’s the most effective at keeping cheatgrass at bay is hard-fought.
“A lot of the energy and intention and money goes to those [post-wildfire] situations,” Riginos said. “My fear is that we’re not putting enough focus on these places where we have this opportunity to hold the line.”
Currently, land managers who steward the least-invaded reaches of Wyoming have a tough argument for funding when they’re competing for limited dollars with weed and pest districts losing their cheatgrass fights.
The Nature Conservancy’s research could help make their case.
“An ounce of prevention is worth a pound of cure,” Riginos said. “How do we do that intelligently?”
