GEOLOGY OF WEST COAST REGION OF UNITED STATES 

 sists of a well-defined zone of gold-bearing quartz 

 veins, including the important group to which the 

 name "Mother Lode" has been applied. It starts in 

 Tulare and Kern counties, broadening to a width 

 of sixty miles in Plumas and Butte counties. In 

 Tehama, Lassen and Plumas counties the belt dis- 

 appears under the lava, reappearing near Redding 

 and extending into Oregon. The veins in general 

 are in the metamorphic rocks, especially the Mari- 

 posa slates, west of the batholith. In the southern 

 part of the State gold veins appear in or near 

 schists included in the granites of Los Angeles, 

 Riverside and San Diego counties. The Grass Val- 

 ley, Nevada City and Mother Lode districts have 

 been the most productive of this great zone of gold 

 veins. Placer deposits skirt the western margin 

 of the entire belt, the economic value of which, 

 especially in the northern portion, is often confined 

 to these secondary deposits. The total gold product 

 of California, which is derived very largely from 

 this belt, from 1848 to 1913, is estimated at $1,588,- 

 087,904. The maximum production was reached 

 in 1852, when the pioneer placer miners produced 

 over eighty-one million dollars, a figure which com- 

 pares well with the total gold production of the 

 United States at the present time. 



An extensive copper belt lies west of the gold 

 deposits, the most productive portion of which is 

 known as the "Foothill Copper Belt," and includes 

 such mines of note as the Copperopolis and the 

 Campo Seco in Calaveras County, and the Dairy 

 Farm mine in Placer County. 



Separated from the main copper belt by the 

 lava tongue mentioned above, are the copper de- 

 posits of Shasta County, which include the largest 

 copper producers of the west coast, such as the 

 Mammoth, Iron Mountain, Bully Hill, Balaklala, etc. 

 These occur in the margins of an acid intrusive 

 rock, which is perhaps an outlying member of the 

 main batholith. 



The second belt containing copper occurs in 

 the northern Coast Ranges and Siskiyou Mountains 

 of California, and reaches well into Oregon. The 

 ores are found chiefly in serpentine and related 

 rocks. Although the belt is extensive, it has not 

 as yet produced important mines. It furnishes to 

 geologists, interesting, puzzling, and as yet unan- 

 swered questions as to the origin of these high- 

 grade lenses of copper ore in serpentine. Nickel 

 ores in Baker and Josephine counties, Oregon, are 

 also found in the serpentine. 



Southeast of the main Sierra Nevada batholith 



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