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Author: Admin | 2025-04-27
The intersection of two major Eocene channels. The primary channel entered from the southeast from the Ralston Divide District about 15 miles away. A smaller tributary channel entered the district from the Damascus District to the north (Lindgren, 1911) where it was highly productive. Within the district, however, the tributary deposits have been largely lost to erosion. The Eocene drainage system included an ancient counterpart to the current Middle Fork of the American River, which followed the same general course as the modern drainage. It flowed westward through the Ralston Divide District and skirted the southern part of the Michigan Bluff District where its gravel deposits were discovered on Michigan Bluff. Between the two districts the channel has been lost to erosion. West of Michigan Bluff, the channel has again been eroded, but reappears in the Paragon Mine in the Forest Hill District where it is known as the Forest Hill Channel. The main gravel deposits in the district are those at Sage Hill and Michigan Bluff adjacent to and below the Michigan Bluff townsite. The gravel exposure at Michigan Bluff covered approximately 40 acres and proved to be one of the most valuable deposits in the district. By 1880, almost all the smaller claims on this deposit were consolidated by the Big Gun Mining Company and operated as the Big Gun Mine, which ultimately produced $1 million by 1882. This deposit has been correlated with the Eocene Forest Hill Channel in the Forest Hill District to the west and the Long Canyon Channel to the east in the Ralston Divide District. In the Forest Hill District, it can be traced for almost 6 miles and produced more than $6.1 million from the district's three main mines, the Paragon, Mayflower, and Dardanelles. Channel morphology is characterized by a flat, trough-shaped channel depression incised in bedrock. Where best exposed at the Paragon Mine near Bath, the bedrock channel was 500 feet wide and 100 feet deep. The bedrock surface is irregular with ridges, swales, and potholes conducive to trapping placer gold. In contrast to the equivalent gravels in the Forest Hill District, which are generally a blue-gray due to a concentration of slate and other metamorphic rock, the Michigan Bluff and Sage Hill gravels are almost exclusively white quartz gravels with some white quartz boulders of up to 20 tons. This difference is likely due to their location upstream of Calaveras
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