View of Upper Bonanza Dam. Construction of the dam started in 1906. The dam was keyed into a four-foot-deep slot in the soft bedrock. It was 225 feet thick at the base, narrowing to 20 feet at the top. The dam was completed in the summer of 1907. Water was delivered to Gold Hill at Grand Forks by two ditch lines and an inverted siphon across the Bonanza Creek valley feeding two hydraulic monitors on Gold Hill. See 1984.234.188, view of the interior of the dam.