Brown's Valley is in north-central Yuba County about 15 miles northeast of Marysville. The Hammonton dredge field is just to the south. The area was mined during the gold rush, when very coarse placer gold was recovered. It was named for a prospector who reportedly recovered $12,000 from a quartz vein in a few weeks in 1850. Much lode mining was done here in the 1860s and 1870s, and intermittent activity continued through World War I. The Dannebroge mine was reopened in 1945 and has been intermittently active since. The lode mines are estimated to have yielded $3 million to $5 million.
The central portion of the district is underlain by a northwest-striking belt of fine-grained greenstone that is classified as metadiabase and andesite porphyry. Amphibolite lies to the east, valley alluvium to the west, and gravels of Yuba River to the south.
A number of nearly west-striking quartz veins in greenstone dip either north or south. The veins range from one to 10 feet thick. The ore contains free gold, pyrite, some galena, and chalcopyrite. Much of the recovered values have been free gold, but the sulfide concentrates often run high. Stoping lengths average around 150 feet, and the veins have been mined to inclined depths of 1700 feet.
Cleveland, Dannebroge, Hibbert and Burris, Jefferson, Pennsylvania, Too Handy.
Lindgren, Waldemar, 1895, Smartsville folio; California: U. S. Geol. Survey Geol. Atlas of the U. S., folio 18, 6 pp.
O'Brien, J. c., 1952, Yuba County, Dannebroge mine: California Jour. Mines and Geology, vol. 48, no. 2, pp. 149-151.
Preston, E. B., 1890, Brown's Valley: California Min. Bur. Rept. 10, pp. 798-799.
Waring, C. A., 1919, Yuba County, Brown's Valley: California Min. Bur. Rept. 15, p. 422.