By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Gold deposits are distributed rather widely throughout Riverside County, but not one of these has been an exceptionally large producer. Before 1893, particularly during 1876-86, there was considerable mining activity, and the aggregate production may have been as much as $1 or $2 million, mostly in lode gold; little placer mining has been done in the county.
The Pinacate and Pinon-Dale districts are the major gold producers in the county, and small amounts of gold have been mined from scattered localities in the Chuckawalla Mountains and the Bendigo district. Total gold production for the county from 1893 through 1959 was 108,800 ounces.
The geology of the mining districts has not been published, but the generalization can be made that most of the gold occurs in quartz veins that occupy fissures in granitic rocks or in country rock near granodiorite bodies (Nolan, 1936b, p. 43-45).
The Pinacate district, in Tps. 4 and 5 S., R. 4 W., a few miles west and southwest of Perris, produced a total of about 104,000 ounces of gold through 1959, all from lodes. The principal mine in this district is the Good Hope mine, originally worked by Mexicans at an unknown date; the property is credited with a production of about $2 million in gold before 1896 (Tucker and Sampson, 1945, p. 133).
The district declined until the mid-1930's at which time attempts were made to rehabilitate the Good Hope and several other mines, but these efforts were largely unsuccessful. During 1943-59 only 3 ounces of gold was produced from the district.
The predominant country rock in the district is granodiorite of undetermined age (Tucker and Sampson, 1945, p. 133, 135, 138-139). Quartz veins, containing free gold and minor sulfides, cut the granodiorite.
The Pinon-Dale district, a large area along the north boundary of Riverside County, includes Tps. 2 and 3 S., Rs. 10 to 12 E.Although Nolan (1936b, p. 44) reported that the district has been known for a long time, published information on it is meager. Production of the district to 1943 was a minimum of 32,000 ounces of gold, and during 1943-59 only 75 ounces was reported. The major mines are the Lost Horse, with an estimated gold output of $350,000, and the New Eldorado.
The country rock of the district consists of granite, schist, and quartzite (Tucker and Sampson, 1945, p. 130-132). The gold occurs in quartz veins, most of which are in the granite.
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