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.
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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.[4] Its station was located on the Union Hill road, southeast of Grass Valley and northwest of Colfax.[5]
The Union Hill mine was a good producer of gold for many years.