A dredge was a huge but simple machine used to mine an ancient river bed for gold, an expensive and powerful improvement on the shovel and rocker box. Miners called it a "goose" because it was fed at the front, digested soil inside while keeping the gold it collected, and expelled excess soil out the back. It was guided by cables and winches and powered by Fremont Powerhouse through a 19-mile extension cord. Excavation at the front used 72 one-ton buckets mounted on a huge boom called a bucket line, which gouged into the soil and carried loose rock into the dredge. Steel cylinders separated the material by size, sending smaller material deeper into the dredge and into sluices that acted like filters. The material was then dumped into a hopper, which fed it into a trommel, a rotating screen. Material that passed through the screen, a mixture of water, gold, dirt, and small gravel called slurry, went to riffle boxes for treatment to extract the gold, while material too large to pass through the trommel went into the tailing stacker and was spewed out the back as tailings.