For the first time in more than a century, migrating salmon have climbed close to the headwaters of the Klamath River’s most far-flung tributaries, as much as 360 miles from the Pacific Ocean in south-central Oregon. The achievement is the clearest indication yet that the world’s largest dam removal project, completed on the river a year ago, will yield major benefits for salmon, the river ecosystem, and the tribes and commercial fishers whose lives revolve around the fish.