 In order to move logs from the plateau above the Lower river , Adams River Lumber constructed several <unk> . The <unk> were elevated wooden troughs filled with water that floated logs down to the valley bottom . The largest of these was at Bear Creek . It incorporated <unk> up to 25 metres ( 82 ft ) high and was capable of moving 3 @,@ 000 @,@ 000 metres ( 9 @,@ 800 @,@ 000 ft ) of logs per month . It was the largest <unk> in North America at its peak . The structures were dismantled after the areas became logged out . 
