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After most of the miners left disappointed, companies arrived with dredges to look for gold. In the Alder Creek Valley, there were five dredges.
Dredges in sizes ranging from a number 2 (the smallest) to a number 16 (the largest) worked the stream and managed to take out between 150 and 200 million dollars in gold!
Dredges work by using a whole string of buckets to drag along the bottom of the stream and dig up bucketfuls of dirt and rock.
The gravel, which contains the free gold, are then dumped into a revolving screen called a trommel. In the trommel it is washed and the oversized gravel is dumped behind the boat with conveyor belt called a stacker.
The gravel which contains the free gold is funneled into sluice boxes where the gold sinks to the bottom where it can be gathered. Gold is much heavier than the other rocks, so it is fairly easy to gather once the lighter sand and gravel is washed away.
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