By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Rio Grande County is in south-central Colorado in the southeastern San Juan Mountains, on the west side of the San Luis Valley. The Rio Grande River crosses the northern part of the county.
In the early 1880's Rio Grande County ranked third in the State in the production of gold, the county's chief metal. Gold output of the county through 1947 was about 257,600 ounces (about $7 million worth) ; however, from 1949 through 1958 it was only 135 ounces. Small amounts of silver, copper, and lead valued at about $330,000 have been recovered from the gold ores.
The Summitville district is in the southwest corner of Rio Grande County, high in the San Juan Mountains.
The earliest discoveries of gold in the San Juan Mountains were in 1870 in the Summitville district and in Arrastre Gulch in San Juan County. The news of these finds started a rush to the region, and within a few years most of the major mining camps were established. The early discoveries in the Summitville district were of placer gold, but available records indicate that placer production in the area was minor, probably less than $10,000 worth. The first lodes were located in 1871, the richest deposits were located by 1873, and large-scale mining began in 1875.
The ore near the surface was oxidized, rich, and easy to beneficiate. By the end of 1887 most of the known oxidized ore had been mined out, and the underlying sulfide ores were much lower grade and more difficult to mill and concentrate. During 1873-87 the Summitville district produced, mostly from the Little Annie mine, about $2,064,000 in gold and silver, 95 percent of which was gold (Steven and Ratte, 1960b, p. 6). Production declined sharply in 1888 and fluctuated considerably in the years through 1925. A deposit discovered in 1926 in the Little Annie group of mines produced, by 1930, about $500,000 in gold from 864 tons of sorted ore. This ore shoot was mined out by the end of 1930, and during 1931-33 the total metal production from the district was only slightly more than $5,000.
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