The Yuba Goldfields, located approximately fifty 50 miles north of Sacramento in
Marysville, California; is the last large gold dredge operation in the United States. Mining for gold using the dredging method began in 1904, by W.C. Hammon.

At this time a wooden hulled bucket-line dredge was only capable of digging to a depth of sixteen 16 feet below water level. Mr. Hammon began a Marysville based company for constructing dredges shortly thereafter. He formed his own subsidiary for building dredges and later moved the building operation to Benicia, California.
 
In the 1930’s twelve 12 dredges operated in the Yuba Goldfields and by 1968, 21 dredges had been built and operated. This allowed for approximately one 1 billion cubic yards of gravel to be mined for more than five million ounces of gold; for a value of about 140 million dollars at the time it was mined.

A deep ore reserve was discovered in 1968. However, due to low gold prices it wasn’t cost effective to construct new machines to mine at the depth of the reserves. Therefore, the gold was left behind. By late 1976, Dredge 21 had operated intermittently and was finally put on a “care and maintenance” status.
 
In 1979, a joint venture was formed between Yuba Natural Resources (the property owners) and Placer Service Corporation. This partnership was formed to mine the deep reserves left behind in 1968. Dredge 21 was brought out of retirement and moved to the deep reserve area.

Dredge 21 was rebuilt with an extended bow gantry, longer digging ladder, new bucket- line, more efficient main drive system, new electrical system conforming to OSHA/MSHA specifications, new hydraulic control system, new control room and gold saving plant. Dredge 21 is powered by electricity purchased from Pacific Gas and Electric (PG & E). The on board recovery system is 100% gravity separation, using no chemicals. With these modifications Dredge 21 began successful mining operations on October 1, 1981, as well as becoming one of the deepest digging gold dredges in the world at 140 feet below water level. In 1992 Cal Sierra Development purchased the operation and operated Dredge 21 until January 2003. Currently the parts from Dredge 21 are being used in the restoration of Dredge 17.