This district is in north-central Nevada County about seven miles northeast of Nevada City. It includes placer deposits in the North Columbia and Columbia Hill areas and lode deposits in the Delhi mine area.
The district was first placer-mined during the gold rush and hydraulicked on a large scale from the middle 1850s to the early 18805. It was named after Columbia Hill, and "North" was added to distinguish it from Columbia in Tuolumne County. The Delhi lode mine was active from the 1860s to the 1890s. Chinese carried on small-scale placer mining from the 1890s to the early 1900's. Some work was done again during the 1930's and the area has been prospected since. The total output of the district is unknown. The placer mines are estimated to have yielded $2 million to $3 million. Lindgren (1911) estimated that 25 million yards of gravel had been removed and 165 million remained. The lode mines have yielded more than $1 million. Beginning in 1966, the U.S. Geological Survey and U.S. Bureau of Mines have studied this district as part of their "heavy metals" programs (see also sections on Badger Hill and North Bloomfield).
Extensive channel deposits lie at the junction of two major streams of the Tertiary Yuba River. A west-trending channel extends through the district from North Bloomfield and continues on to Badger Hill, and a branch enters the district from Blue Tent to the south. In places the gravels are as much as 500 feet thick. The lower gravels are coarse while upper bench gravels are fine. Much sand and clay are present. Bedrock is phyllite of the Delhi formation (Carboniferous). Several gold-quartz veins have yielded high-grade ore.
(all lode) Delhi $1 million, Enterprise, Grizzly Ridge, St. Gothard.
Hobson, J. B., and Wiltsee, E. A., 1893, Columbia Hill district: California Min. Bur. Rept. 11, pp. 305-308.
Irelan, William, Jr., 1888, Columbia Hill district: Caljfornia Min. Bur. Rept. 8, pp. 444-447.
lindgren, Waldemar, 1900, Colfax folio, California: U. S. Geol. Survey Geol. Atlas of the U. S., folio 66, 10 pp.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geol. Survey Prof. Paper 73, p. 139.
Mac Boyle, Errol, 1919, Nevada County, North Columbia mining district: California Min. Bur. Rept. 16, pp. 48-51.