This district is in central San Diego County in Cuyamaca Rancho State Park about 50 miles east-northeast of San Diego.
The Stonewall mine, the chief source of gold in the district, was discovered in 1870, reportedly by either William Skidmore or Charles Hensley. It operated under difficulties until 1886, when it came under the control of an ex-Governor of California, Robert W. Waterman. The mine was highly productive from then until 1895. There has been very little mining activity in the area since. The remaining equipment and surface plant of the famous old mine have been made into an outdoor museum. The mine has a total output that has been variously estimated at $2 million to $3 million.
The Stonewall mine area is underlain by mica schist, granodiorite, and gneiss. A large body of gabbro and related rocks lies immediately to the west. Ore was recovered from several north-trending and steeply dipping quartz veins. At the Stonewall mine, the vein is as much as 20 feet thick. The ore contained free gold, abundant sulfides including pyrrhotite and pyrite, and occasionally small amounts of gold tellurides. The famous ore shoot at the Stonewall mine had a pitch length of about 300 feet.
Creasy, S.C., 1946, Geology and nickel mineralization of the JulianÂ· Cuyamaca area, San Diego County: California Div. Mines Rept. 42, pp. 15-29.
Everhart, D. L., 1951, Geology of the Cuyamaca Peak quadrangle, San Diego County: California Div. Mines Bull. 157, pp. 51-136.
Hanks, H. G., 1886, The Stonewall mine: California Min. Bur. Rept. 6, pt. 1, pp. 89-90.
Merrill, F. J. H., 1916, San Diego County, Stonewall mine: California Min. Bur. Rept. 14, pp. 660-662.
Weber, F. Harold, Jr., 1963, San Diego County, gold: California Div. Mines and Geology County Rept. 3, pp. 115-167.