First Nations in British Columbia’s central Interior are measuring the impacts of a massive landslide that blocked the Chilcotin River for days, followed by a subsequent torrent of water that sent trees and debris downstream. The Williams Lake First Nation says village sites that date back 4,000 years were swept away as the Chilcotin River carved away riverbanks, while the Tsilhqot’in National Government says critical salmon migration routes are seriously damaged and the threat of more slides exists. The landslide south of Williams Lake that dammed the Chilcotin River last week broke free on Monday, sending raging water, trees and debris downstream to the Fraser River, which flows through the Lower Mainland to Georgia Strait. Two heritage sites located along the banks of the Chilcotin River near the Farwell Canyon…