The Upper Green River is Wyoming’s take on the Serengeti plains of Africa—a natural bottleneck where wildlife move through ancient migratory pathways. In the lower 48’s longest big-game migration, pronghorn travel from summer ranges in the Greater Yellowstone’s mountain highlands, to winter stomping grounds in the Upper Green’s sagebrush-covered valley.
The Upper Green River site is a stronghold for sage grouse, the West’s signature native game bird now considered for listing under the Endangered Species Act.
The open vistas of this mountain-to-high-desert ecosystem are rapidly dwindling. Humans are jamming historic migratory corridors and other wildlife habitat with an expanding web of roads, oil and gas wells, pipelines, housing developments, and fences.
Location
Southwest Wyoming, between the high peaks of the Wind River, Gros Ventre and Wyoming ranges
Size
More than one million acres
Plants
The heart of the Upper Green River site has vast stretches of Wyoming and mountain big sagebrush. Transition areas between sagebrush and grassy wetland areas provide habitat for over two-dozen rare or endangered plant species. Rare glacial “potholes” in the mountainous regions have developed special soils that also support rare plants.
Animals
The Upper Green River’s riparian and wetland areas are the most extensive in Wyoming, providing habitat for the endangered Colorado cutthroat trout, and breeding sites for five bird species of special concern, including reintroduced trumpeter swans. Sagebrush supports the largest population of sage grouse in the state, and big-game species such as mule deer (second largest herds in Wyoming), pronghorn and elk.
Why the Conservancy Selected this Site
Escalating levels of human activity in the Upper Green River site threaten to block ancient migratory pathways, severing the routes big-game animals have used for thousands of years. If these species are to sustain healthy populations, they must have access to the valley’s critical winter range. Several species, especially sage grouse and mule deer, are showing signs of sensitivity to disturbances on the landscape.
What the Conservancy Has Done/Is Doing
The Conservancy is sharing a scientific planning process with the oil and gas industry and government agencies for designing off-site mitigation in the Upper Green River site. In the future, we hope this ecologically-sound methodology will be used industry-wide to strengthen regulations and inform future development decisions.
