Federal judges ruled that the Forest Service's analysis of how snowmobiling will affect wildlife in a Montana forest was insufficient.
The 9th U.S. Circuit Court of Appeals sided with environmentalists challenging the service's management of the Beaverhead-Deerlodge National Forest.
In 2010, the service promulgated a new management plan for the 3.35-million-acre forest that included opening about 2 million acres for snowmobile use.
That was actually less than was previously available to snowmobiles, but the use of the vehicles has been on the rise.
Environmentalists led by WildEarth Guardians challenged the service's analysis of the plan under the National Environmental Policy Act.
The San Francisco-based 9th Circuit sided with the group on several grounds, reversing part of a lower-court decision.
Specifically, the court held that the service did not properly identify how or where snowmobiles would influence big game habitats, or how those interactions could be limited.
The court also held that the service did not provide adequate opportunity for public input on the plan.
"We conclude that the [environmental impact statement] does not provide the public adequate access to information about the impact of snowmobiles on big game wildlife and habitat," wrote Judge Richard Paez.
However, the court sided with the service on other grounds, including that it adequately considered the impact of snowmobiles on other recreational activities, such as mountain biking, hiking and fishing. It sent the case back to the lower court for further proceedings.