A proposal to bring down four hydroelectric dams near the California-Oregon border has cleared a major regulatory hurdle. Federal regulators on Thursday allowed the utility that operates the dams to exit its license, setting the stage for the largest dam demolition project in U.S. history to save imperiled migratory salmon. PacifiCorp will surrender its license for the dams on the lower Klamath River to a nonprofit and the states of Oregon and California. The aging dams essentially cut the river in half for migrating salmon important to tribes. If the dams remained, the utility would likely have to spend hundreds of millions of dollars to retrofit the structures to comply with today’s environmental laws. Klamath River water has been a point of contention for decades, especially in drought years. An agreement that includes tribes, farmers, commercial fishing interests and other stakeholders was drafted a decade ago but its implementation has hit many snags.