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Nr. Peter V. O'C ,nor Page 6 September 23, 1985 approximately 80 feet wide. On Horsfal Hill, a series of massive bull quartz veins 5 to 50 feet wide form wall-like outcrops 10 to 20 feet high. In outcrop the Hoosier Reef is pale pink or reddish in color and consists largely of massive, milky bull quartz. The Hoosier Reef is very ti ht d tad rinds of shearin end silicification, which were followed by the deposition o e massive bull quartz. One of the most productive centers of mineralization in the Gold Hill district is located east of the town of Gold Hill, within an area about four miles square. It encompasses the area between Left Hand Creek on the north and the community o[ Summerville on the south, end includes the important Slide, Cold Spring, Red Cloud, Horsfal, Cash, Alamakee, Gold Ring, Black Cloud, White Cloud, and Victoria veins. All of the productive veins strike northeast at almost right angles to the Hoosier Reef end dip steeply to the northwest. They can be traced on the surface for more than half a mile, and are from 1 to 5 feet wide. All of the important ore deposits in this area are within 3000 feet o[ the northeast side of the Hoosier Reef. There are no productive veins southwest of the Hoosier Reef in the area between Left Hand Creek and Summerville. This stron¢ spatial relationship to the Hoosier Reef indicates that the mineral- tot~enetrete the massive bull quartz rosier Ree[ served as a dam to the circ ore solutions which concen ra a on a nor east st e o t e ree . These same geologic conditions were an important consideration in the selection of the Time, Wynona, and Hazel A. mines for use es underground water storage areas. Because of the crystalline nature of the Boulder Creek granite, the ground water that is found in the bedrock is only present where the granite has been fractured. Generally, the openings of these fractures (joints and [cults) decrease in size with increasing depth, and the chances oY obtaining water are significantly reduced below a depth of 300 feet. All of the veins near the proposed water storage area are particularly narrow and tight, and contained within very competent wallrocks that are nearly impervious. Water that has been pumped from the Cash Mine and stored underground in the Hazel A. edit has remained at a nearly constant level behind the bulkhead throughout the year. A.comparison of the level of the ground water on lath sides of the Hoosier Reef indicates that the reef acts es an impervious water barrier. Although Boulder Creek granite is found on both sides of the Hoosier Ree[ in the area near Gold Hill, there is no evidence that the ground water systems are connected. Whereas ell of the J~U mine shafts on the east side of the reef are flooded, and the mine workings contain tens o[ millions of gallons of water, the ground ~ water level to the west of the Hoosier Reef does not reflect any recharge from these extereive underground mine workings.