This district is in western Mariposa County in the vicinity of the towns of Bagby and Bear Valley. It is in the Mother Lode gold belt.
The streams were placer-mined early in the gold rush, and the Pine Tree and Josephine veins were discovered in 1849. Part of the area was on the Las Mariposa Spanish land grant of General John C. Fremont. Bagby was first known as Benton Mills, named by Fremont for Senator Thomas Hart Benton, his father-in-law. It was renamed in the 1890s for A. Bagby, a hotel owner. The town was a stop on the Yosemite Valley Railroad, which once extended up the Merced River canyon to Yosemite National Park.
Gold mining activity continued until around 1875. There was mining in the district again in the early 1900s. The Pine Tree-Josephine mine was worked on a major scale from 1933 to 1944, and the Red Bank mine has been active in recent years. Part of the area, including the old town of Bagby, was inundated by the Exchequer Reservoir in 1967.
In this district the Mother Lode gold belt is about 1.5 miles wide. It is underlain by northwest-striking beds of slate, phyllite, and metasandstone of the Mariposa Formation (Upper Jurassic), with greenstone and green schist both to the west and southeast (see fig. 18, page 95). A belt of serpentine extends northwest through the central portion of the district and is structurally important in relation to some of the gold-bearing veins.
There are several northwest-trending vein systems that consist of quartz veins and stringers with brecciated slate, schist, and associated bodies of pyritic ankerite and mariposite-quartz rock. These vein systems are often scores of feet in thickness. The ore contains free gold, pyrite, and arsenopyrite with small amounts of chalcopyrite, galena, millerite, sphalerite, and niccolite. Milling ore averaged 1/7 to 1/2 ounce of gold per ton. In places high-grade ore is abundant. The ore shoots had stoping lengths of up to 600 feet, and the veins were mined to an inclined depth of 1500 feet.
Dolman, French $116,000+, Jumper, Juniper, Live Oak, Mexican I $50,000, Oso $50,000+, Pine Tree-Josephine $4 million+, Queen Specimen, Red Bank $100,000+, Specimen.
Bowen, O. E., Jr., 1957, Mariposa County, Pine Tree and Josephine mine: California Journal of Mines and Geology, vol. 53, pp. 151-155.
Costello, W.O., 1921, Mariposa County, Bagby district: California Min. Bur. Rept. 17, pp. 91-92.
Knopf, Adolph, 1929, Mariposa Estate mines: U. S. Geol. Survey Prof. Paper 157, pp. 83-84.
Logan, C. A., 1935, Pine Tree and Josephine mines: California Div. Mines Bull. 108, pp. 186-189 and plate X.
Ransome, F. lo, 1900, Mother lode distrid folio: U. S. Geol. Survey Gear. Atlas of the U.S., folio 63, 11 pp.
Storms, W. H., 1900, The Mother lode region-Mariposa County: Calif. Min. Bur. Bull. 18, pp. 143-146.