SEATTLE (AP) \u2014 A conservation group is threatening to sue the Trump administration over its sudden reversal of plans to restore grizzly bears in the North Cascade mountain range of Washington state. The Center for Biological Diversity\u00a0sent a letter\u00a0Wednesday saying it intends file a federal lawsuit in 60 days unless the Interior Department resumes its efforts to reintroduce the apex predator. The center said the Endangered Species Act mandates the bears' recovery. The Interior Department called the threat frivolous in an emailed statement. Grizzly bears once thrived in the North Cascades and many other areas throughout the American West. But they were shot, poisoned and trapped nearly to extinction \u2014 many with the reward of a government bounty \u2014 as white settlers encroached on their habitat. They were listed as threatened under the Endangered Species Act in 1975. The government's recovery efforts have focused on six areas of Idaho, Montana, Wyoming and eastern Washington state \u2014 especially the area around Yellowstone National Park, where the population has increased to about 700 bears. But conservationists have long considered the North Cascades, one of the largest remaining wild areas in the country, a prime location for restoring the bears. Just a few are believed to remain there, but experts say the area's prime habitat could support a population of 280. The Interior Department in 2015 began planning to bring bears from other regions to the North Cascades, a halting process that seemed to get a boost in 2018 when then-Interior Secretary Ryan Zinke announced his support. Zinke later resigned amid ethics investigations, and earlier this month, Interior Secretary David L. Bernhardt\u00a0announced the agency was scrapping the plans. \u201cThis is another frivolous lawsuit by a radical special interest group in their quest to have the courts impose their priorities for species protection rather than the career experts from the National Park Service and U.S. Fish and Wildlife Service," the Interior Department said in an emailed statement. \u201cConcerns from local area residents were clear in that they did not want this plan to move forward, and it is well within our legal authority to not proceed with this plan.\u201d Rep. Dan Newhouse, a Republican who represents central Washington state in Congress, has said local residents don\u2019t want a larger population of grizzlies there. A majority of the people who provided public comments to the government supported bringing grizzlies to the back country in and around North Cascades National Park, according to public polling as well as comments submitted to the government. Critics have contended most of that support is from people in liberal cities like Seattle and Bellingham, rather than local residents of central Washington who might have livestock or pets attacked by the bears, or who fear being attacked themselves.