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GEOLOGIC GUIDEBOOK ALONG HIGHWAY 49 



[Bull. 141 



Another major gold-mining operation in Grass Valley is being car- 

 ried on by the Idaho-Maryland Mines Corporation. Its holdings include 

 the Old Brunswick, New Brunswick, Idaho, and Eureka mines and many 

 smaller workings. The New Brunswick shaft is 3450 feet deep and the 

 Idaho is 2700 feet deep via shaft and winze. A successful attempt at shaft 

 sinking by core drilling was made by the Idaho-Maryland. The Idaho 

 No. 2 shaft was sunk 1000 feet into serpentine by this method using a 

 Newsom drilling machine developed at the Idaho-Maryland. The drill 

 cores are five feet in diameter and weigh several tons each. Many of these 

 cores are piled about the entrance to the shaft. Although the Idaho-Mary- 

 land is not as large an operation as the Empire-Star, it is still among the 

 six largest gold mines in California, and has a recorded production of 

 $64,240,543. Very complete, up-to-date ore-treatment plants are con- 

 nected with both Idaho-Maryland and Empire-Star mines. 



The Golden Center mine is located in the heart of the business dis- 

 trict of Grass Valley. Although the surface extent of the Golden Center 

 property is not great the mine was rich and ore worth more than $2,500,- 

 000 was taken from it before litigation forced a shut down. The Golden 

 Center is currently idle. The deepest shaft is 1900 feet as measured along 

 the incline. 



The Spring Hill mine northeast of Grass Valley is a small but prom- 

 ising operation which is active at the present time. It is one of the neatest, 

 best maintained properties in the gold country and its headframe and mill 

 have been photographed repeatedly for various publications. The main 

 shaft is about 1900 feet deep in diabase and serpentine wall rocks. The 

 recorded production, most of which has been within the last 20 years, is 

 $300,000. 



Midway between Grass Valley and Nevada City is the old mining 

 camp of Town Talk. Little remains to mark the site except a modern 

 gasoline station and eating house. Historian Glasscock has it that Town 

 Talk came about partly as an act of God and partly as a practical joke. 

 An old saloon sign bearing the words Town Talk is supposed to have been 

 stranded in the vicinity of the camp by flood waters of Deer Creek. Some 

 wag fished the sign out and stuck it up on the hill and the camp was 

 thereafter known by that name. 



Nevada City, four miles northeast of Grass Valley, has been a 

 famous lode-gold mining center although the mines there are currently 

 idle. James Marshall passed through there seeking a placer bonanza in 

 the summer of 1848 but missed making a strike. The first settlers arrived 

 in 1849 and the placers attracted a large population within a few months. 

 Known originally as Coyoteville, because of the local method of tunnel- 

 ing called coyoteing, the name Nevada City was evolved after a dispute 

 with the state of Nevada over priority rights to that name. A total of 

 $8,000,000 in placer gold is said to have been taken from the vicinity. 



Nevada City is county seat of Nevada County and, like Grass Valley, is 

 full of pioneer landmarks such as the Wells-Fargo Express Office site 

 established in 1853, fire-houses built in the 1860 's, and a remnant of 

 Chinatown. It is situated on Highway 20, which connects with Reno and, 

 like Grass Valley, was once connected to the transcontinental rail route 

 of the Southern Pacific. 



The principal lode mines of Nevada City are the Lava Cap, Murehie, 

 Champion, and Providence. The Nevada City assay office is credited with 

 assaying the first ore taken from the Comstock lode. 



The Lava Cap mine has a recent history dating from 1933. In its ten 

 years of operation it grossed about $12,000,000 in gold and silver! The 

 mine is 2700 feet deep and has over five miles of lateral workings. The 

 Murehie was Avorked in a small way in the 1890 's but major production 

 took place in the 1930 's. The mine is now owned by the Empire Star 

 Mines Company, Ltd., and is currently idle. It was an exceedingly pro- 

 ductive mine before the last World War but few figures on it are avail- 

 able. The Champion and Providence mines have been worked discon- 

 tinuously, with indifferent success, since the early day lode-mining 

 period of the 1860 's and 1870 's. The Nevada City mines lie at the fringe 

 of the Grass Valley district and the ore shoots have not persisted at 

 depth as have those in the heart of the district. 



West from Nevada City, Highway 49 passes through a thick series 

 of Tertiary gravels which lie at the southern base of a ridge of rhyolite 

 tuff and andesite. These deposits have been extensively hydraulicked 

 and placered. Hydraulic pits and faces of moderate size can be seen on 

 both sides of the highway. West of the gravels the granocliorite outcrops 

 are full of dark inclusions or enclaves. These vary in size from fractions 

 of an inch to one foot in diameter. Enclaves are common in many granitic 

 batholiths and are formed either by magmatic segregation of various 

 mineral constituents or by inclusion and partial assimilation of wall 

 rocks caught in the invading magma. In most cases they carry a greater 

 proportion of dark minerals than the matrix rock and have a somewhat 

 different texture. The latter may be either finer or coarser than the 

 including rock and may differ in many other ways. The enclaves west of 

 Nevada City are unique in that they carry a large proportion of the 

 mineral pyrite. Pyrite occurs only in the enclaves, not in the matrix 

 rock, and probably was a constituent of the assimilated rock from which 

 the enclaves formed. The texture is granitic but the crystals are finer 

 than those in the matrix rock, which is essentially a biotite-hornblende 

 granodiorite. Excellent exposures of these rocks may be seen in roadcuts 

 1.2 miles west of Nevada City. 



Immediately west of the enclave locality is the contact between the 

 granodiorite and meta-volcanic greenstones. Lindgren 's map shows these 

 to be in the Calaveras formation but separate from greenstones lying a 

 quarter of a mile to the west. Two miles farther to the northwest is a 



