Union Hill, California
|Elevation||2,700 ft (823 m)|
|Time zone||UTC-8 (Pacific (PST))|
|• Summer (DST)||UTC-7 (PDT)|
Gold mining is recorded as early as January 30, 1851. A number of mines yielded eighty dollars per ton at times. Sulfurets were said to yield 420 dollars per ton. First arrastres were in use, then a number of stamp mills. 
The Union Hill School District, established in 1868, continues to operate in Grass Valley, though at a different location.
Beginning in 1876, travelers could reach Union Hill via the Nevada County Narrow Gauge Railroad. Its station was located on the Union Hill road, southeast of Grass Valley and northwest of Colfax.
The Union Hill mine was a good producer of gold for many years.
- U.S. Geological Survey Geographic Names Information System: Union Hill, California
- Durham, David L. (1998). California's Geographic Names: A Gazetteer of Historic and Modern Names of the State. Quill Driver Books. p. 571. ISBN 1-884995-14-4.
- Bean, Edwin F. (1867). History and Directory of Nevada County. p. 220.
- Preston, E. M. (1886). Nevada County, the famous Bartlett pear belt of California. Digitized Aug 29, 2008. Nevada County Land and Improvement Association. Brown & Calkins, Printers. p. 51.
- Shearer, Frederick E. (1882). The Pacific Tourist: J.R. Bowman's Illustrated Transcontinental Guide of Travel, from the Atlantic to the Pacific Ocean (Digitized Jan 30, 2008 ed.). J.R. Bowman. p. 253.