Here is a excerpt from the book "Gold Districts of California" published by the California division of mines and geology regarding the Sierra Nevada province.

SIERRA NEVADA PROVINCE 

Geology

The Sierra Nevada, the dominant mountain range in California, is approximately 400 miles long, with steep multiple scarps on its eastern flank and a gentle western slope. It has been the source of the bulk of the state's gold production and contains the richest and the greatest number of districts. 

The main mass of the Sierra Nevada is a huge batholith of granodiorite and related rocks that is intrusive into metamorphosed rocks of Paleozoic and Mesozoic age. The metamorphic rocks occur largely along the western foothills and in the northern end of the range. They are complexly folded and faulted and consist of a number of major rock units. The principal units are the slates, phyllites, schists, quartzites, hornfels, and limestones of the Calaveras Formation (Carboniferous to Permian); the Amador Group (Middle and Upper Jurassic) of metasedimentary and metavolcanic rocks; the Mariposa Formation (Upper Jurassic), much of which is slate; schists, phyllites, and quartzites of the Kernville Series (Jurassic or older) in the southern Sierra Nevada; and a vast amount of undifferentiated pre-Cretaceous greenstones and amphibolites. 

In addition, there are numerous intrusions of basic and ultra-basic rocks, many of which are serpentinized. The serpentine bodies apparently have been structurally important in the localization of some goldbearing deposits and often are parallel to or occur within the belts of gold mineralization. Also, there are numerous dioritic and aplitic dikes that are closely associated with gold-bearing veins. 

Lode Deposits

Much of the gold mineralization is in the belt of metamorphic rocks that extends along the western foothills and in the northern end of the range, although some important districts are in granitic rocks. Some are associated with small intrusions or stocks related to the Sierra Nevada batholith. The richest as well as the largest number of lode-gold deposits are in the northern and central portions of the range. In the Butte-Plumas County area at the northern end of the Sierra Nevada, the gold belt is nearly 70 miles wide. Continuing south it narrows and dies out almost completely in the Fresno-Tulare County area but appears again in Kern County in the southern end of the range. There are a few widely separated districts along the steep eastern flank of the range. 

The most productive lode-gold districts in the northern end of the Sierra Nevada have been the Alleghany, Crescent Mills, Downieville, Forbestown, Graniteville, Grass Valley, Johnsville, Nevada City, and Sierra City districts. In the central portion the most productive and best-known districts are in the Mother Lode gold belt. Although the entire foothill region of the Sierra Nevada is sometimes loosely termed the "Mother Lode Country," technically the Mother Lode is a 120-mile-long system of linked or en echelon gold-quartz veins and mineralized schist and greenstone that extends from the town of Mariposa, north and northwest to northern El Dorado County. 

The most production portion of the Mother Lode has been the 10-mile segment between Plymouth and Jackson in Amador County. Other major sources of gold in the Mother Lode have been the Angels Camp, Bagby, Carson Hill, Coulterville, Georgetown, Greenwood, Jacksonville, Jamestown, Kelsey, Mount Bullion, Nashville, and Placerville districts. 

Although the terms "East Gold Belt" and "West Gold Belt" have been arbitrarily coined to describe the gold deposits east and west of the Mother Lode, each contains extensive systems of gold-bearing veins. Unfortunately few systematic studies have been made of these belts. The principal sources of gold in the East Gold Belt have been the Grizzly Flat, West Point, Sheep Ranch, Soulsbyville, Confidence, Clearinghouse, Hire Cove and Kinsley districts. The most important in the West Gold Belt have been the Ophir, Shingle Springs, Hunter Valley, Hodson, and Hornitos districts. To the southeast in Madera and Fresno Counties there are some gold districts, but they have been much less productive than those to the north. In the southern Sierra Nevada, in Kern County, considerable quantities of lode gold have been mined in the Cove district and from scattered areas to the west and south that include the Keyesville, Clear Creek and Loraine districts.

Gold has been mined from a few districts along the east flank of the Sierra Nevada, the most productive having been the Bishop Creek district, Inyo County, and the Homer, Mammoth and Jordan districts in Mono County. Appreciable quantities of by-product gold have been recovered from the Sierra Nevada copper belts in the western foothills (see separate section below) and the Plumas County copper districts. Some has been recovered from tungsten mines on the east flank of the Sierra Nevada. 

Placer Deposits

The alluvial or placer deposits of the western Sierra Nevada have contributed more than 40 percent of California's total gold output. They are divisible into the Tertiary (older) deposits, which consist predominantly of quartzitic gravels, and the Quaternary (younger), which are in and adjacent to the present stream channels. The Tertiary channel deposits have been mined by hydraulic and drift mining, while the greatest yield from the Quaternary deposits has been from dredging. The flush production of the gold rush was from Recent surface placers that were mined by small-scale methods. These surface placers have largely been exhausted. 

The most productive Tertiary channel deposits have been in the Magalia, Cherokee, and BangorWyandotte districts of Butte County; the La Porte and Sawpit Flat districts of Plumas County; the Smartsville district of Yuba County; the Gibsonville, Downieville, Poverty Hill, Poker Flat, Brandy City, and Alleghany districts in Sierra County; the North Bloomfield, North Columbia, North San Juan, French Corral, Scotts Flat, You Bet and Washington districts, Nevada County; Dutch Flat, Gold Run, Forest Hill, Iowa Hill, Damascus, Last Chance and Michigan Bluff districts. Placer County; Placerville district. El Dorado County; Fiddletown and Volcano districts, Amador County; Mokelumne Hill and Vallecito districts, Calaveras County, and the Columbia district of Tuolumne County. 

All of the major streams and their tributaries that flow across the gold-bearing areas have been placermined, many of them several times. The rivers that have yielded the most gold have been the Feather, Yuba, and American Rivers, but large quantities have been recovered from the Bear, Cosumnes, Mokelumne, Stanislaus, Tuolumne, Merced, and Kem Rivers and some from the Chowchilla, Fresno, Kings, White, and San Joaquin Rivers. The two greatest dredging fields are the Hammonton district on the lower Yuba River, Yuba County, and the Folsom district adjacent to and south of the Lower American River in Sacramento County. Other major dredging fields were on Butte and Honcut Creeks and the lower Feather River at Oroville in Butte County; Lincoln, Placer County; Michigan Bar, Sacramento County; Camanche in Calaveras and San Joaquin Counties, La Grange in Stanislaus County and Snelling in Merced County. 

Alleghany

Alleghany is in southwestern Sierra County. This district is in a belt of gold mineralization that extends from Goodyear's Bar, south and southeast through Forest, Alleghany, Chip's Flat, and Minnesota. This gold-bearing belt continues south to the Washington district in Nevada County. The Downieville and American Hill districts are to the east, and the Pike district is to the west. 

History. The streams in the area were placer-mined soon after the beginning of the gold rush, and the Forest diggings were discovered in the summer of 1852 by some sailors. Some of these sailors were "Kanakas" or Hawaiians who also had deserted their ships in San Francisco. Forest, first known as Brownsville and then Elizaville, got its present name in 1853. The Bald Mountain and other drift mines were highly productive from then until around 1885. Hydraulic mining was done at Minnesota and Chip's Flat during these years. The town of Alleghany was named for Alleghany, Pennsylvania. 

Quartz mining was reported to have begun in the district in 1853 at the German Bar and Irelan mines. Although the quartz mines were moderately productive until the 1870s, drift mining was the principal source of gold then. The rediscovery of the Tightner vein in 1904 by H. F. Johnson (erroneously given as 1907 in many reports) led to the revival of lode mining, which continued until 1965.