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Gold specimen showing free gold in rock - Nevada State Museum
Au
Atomic Number = 79, Atomic Weight = 196.967
Color = Gold-yellow, brass-yellow, pale-yellow
Specific gravity = 15.6 to 19.3
Hardness = 2 ½ to 3
Cleavage = none
Best Field marks = gold/yellow color, high specific gravity, malleability
Melting point = 1945 degrees F (1063 degrees C)
Environment: Gold is deposited in veins, igneous rocks, and hydrothermal replacements. Gold is also found as "free gold" in placer deposits. Placer gold is gold that has weathered out of load deposit and redeposited in a sedimentary deposit usually by the action of water. Gold is often associated with pyrite and arsenopyrite in lode deposits.
History: Gold can be found throughout the west but the gold rush to California in 1849 set the stage for much of the exploration of the other western states.
The deep load mines of California fame included the Empire-Star group of Grass Valley, the Kennedy in the Jackson/Plymouth area,and the Sixteen to One mine near Alleghany. Some of the large hydraulic mines were Badger Hill in Nevada County, Dutch Flat in Placer County, and La Porte in Plumas County. The hydraulic mines were extremely destructive in the impacted area. This type of mining was carried out by forcing huge quantities of water through a "cannon" to wash away the old Tertiary river channels located throughout the northern portion of the mother load areas of the Sierra mountains.
Geology of the deposits of the Sierra Nevada: The Sierra Nevada mountains consist of a huge batholith of granodiorite that is intrusive into metamorphosed rocks of the Paleozoic and Mesozoic periods. These rocks are highly folded and faulted. There are many diotitic and aplitic dikes where gold-bearing veins are found. The placer deposits consist of either gold weathered out of a load bearing formation or contained within the ancient river gravels known as Tertiary gravels. These old stream beds are mapped in many areas and were the basis for the hydraulic mining operations. The old river channels can be often be seen as a "blue" streak of gravel high on a hillside.
Large Gold Nuggets of California:

An interesting note is that despite the geological studies that point out that there is still a tremendous reserve of gold in California, most of the gold mines in the United States are located in other states such as North Dakota, Nevada, and Arizona.
For basic information on gold prospecting in the desert, James Klein's book Where to Find Gold in the Desert is one of the best.
| An eye loupe can give you the edge to identify rich ore from false hopes. I always carry one when I'm prospecting. Click on the image to see them at the store. |
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REFERENCE: Fire Assaying by Shepard and Dietrich and The Prospector's Guide by Steven and Mary Taylor and Gold Districts of California, Bulletin 193 by William B. Clark, Geologist, California Division of Mines & Geology.
Don't forget to checkout the information on gold from the California Resources Dept.