Gold in California
Encyclopedia
Gold in California became highly concentrated there as the result of global forces operating over hundreds of millions of years. Volcanoes, tectonic plates and erosion all combined to concentrate billions of dollars worth of gold
in the mountains of California
. During the California Gold Rush
, gold-seekers known as "Forty-Niners" retrieved this gold, at first using simple techniques, and then developing more sophisticated techniques, which spread around the world.
Scientists believe that over a span of at least 400 million years, gold that had been widely dispersed in the Earth’s crust became more concentrated by geologic
actions into the gold
-bearing regions of California
. Only gold that is concentrated can be economically recovered. Some 400 million years ago, California lay at the bottom of a large sea; underwater volcano
es deposited lava
and minerals (including gold) onto the sea floor; sometimes enough that islands were created. Between 400 million and 200 million years ago, geologic movement forced the sea floor and these volcanic islands and deposits eastwards, colliding with the North America
n continent, which was moving westwards.
Beginning about 200 million years ago, tectonic pressure
forced the sea floor beneath the American continental mass. As it sank, or subducted
, beneath today's California, the sea floor heated and melted into very large molten masses (magma
). Being lighter and hotter than the ancient continental crust
above it, this magma forced its way upward, cooling as it rose to become the granite
rock found throughout the Sierra Nevada and other mountains in California today — such as the sheer rock walls and domes of Yosemite Valley
. As the hot magma cooled, solidified, and came in contact with water, minerals with similar melting temperatures tended to concentrate themselves together. As it solidified, gold became concentrated within the magma, and during this cooling process, veins of gold formed within fields of quartz
because of the similar melting temperatures of both.
As the Sierra Nevada and other mountains in California were forced upwards by the actions of tectonic plates, the solidified minerals and rocks were raised to the surface and exposed to rain, ice and snow. The surrounding rock then eroded
and crumbled, and the exposed gold and other materials were carried downstream by water. Because gold is denser than almost all other minerals, this process further concentrated the gold as it sank, and pockets of gold gathered in quiet gravel beds along the sides of old rivers and streams.
The California mountains rose and shifted several times within the last fifty million years, and each time, old streambeds moved and were dried out, leaving the deposits of gold resting within the ancient gravel beds where the gold had been collecting. Newer rivers and streams then developed, and some of these cut through the old channels, carrying the gold into still larger concentrations.
The Forty-Niners of the California Gold Rush
first focused their efforts on these deposits of gold, which had been gathered in the gravel beds by hundreds of millions of years of geologic action.
. Modern estimates by the U.S. Geological Survey are that some 12 million ounces (373 t) of gold were removed in the first five years of the Gold Rush (worth approximately US$7.2 billion at November 2006 prices).
By 1853, the first hydraulic mining
was used. In hydraulic mining, (which was invented in California) a powerful stream of water is directed at gold-bearing gravel beds; the gravel and gold then pass over sluices, with the gold settling to the bottom. By the mid-1880s, it is estimated that 11 million ounces (342 t) of gold (worth approximately US$6.6 billion at November 2006 prices) had been recovered via "hydraulicking."
The final stage to recover loose gold was to prospect for gold in the flat rivers of California’s Central Valley
and other gold-bearing areas of California (such as Scott Valley
in Siskiyou County). By the late 1890s, dredging technology (which was also invented in California) had become economical, and it is estimated that more than 20 million ounces (622 t) were recovered by dredging (worth approximately US$12 billion at November 2006 prices).
Gold-seekers also engaged in "hard-rock" mining
, that is, extracting the gold directly from the rock that contained it (typically quartz) Once the gold-bearing rocks were brought to the surface, the rocks were crushed, and the gold was separated out (using moving water), or leached out, typically by using arsenic
or mercury
. Eventually, hard-rock mining wound up being the single largest source of gold produced in the Gold Country.
s, more than at any other time in the historical record for Northern California
, before the 1906 San Francisco earthquake
. Previously interpreted as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and due to large seasonal sediment loads in coastal bays that overlie faults as a result of mining of gold inland.
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
in the mountains of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. During the California Gold Rush
California Gold Rush
The California Gold Rush began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California. The first to hear confirmed information of the gold rush were the people in Oregon, the Sandwich Islands , and Latin America, who were the first to start flocking to...
, gold-seekers known as "Forty-Niners" retrieved this gold, at first using simple techniques, and then developing more sophisticated techniques, which spread around the world.
Geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
actions into the gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
-bearing regions of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. Only gold that is concentrated can be economically recovered. Some 400 million years ago, California lay at the bottom of a large sea; underwater volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es deposited lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
and minerals (including gold) onto the sea floor; sometimes enough that islands were created. Between 400 million and 200 million years ago, geologic movement forced the sea floor and these volcanic islands and deposits eastwards, colliding with the North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n continent, which was moving westwards.
Beginning about 200 million years ago, tectonic pressure
Tectonic Plates
Tectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...
forced the sea floor beneath the American continental mass. As it sank, or subducted
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
, beneath today's California, the sea floor heated and melted into very large molten masses (magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
). Being lighter and hotter than the ancient continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
above it, this magma forced its way upward, cooling as it rose to become the granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
rock found throughout the Sierra Nevada and other mountains in California today — such as the sheer rock walls and domes of Yosemite Valley
Yosemite Valley
Yosemite Valley is a glacial valley in Yosemite National Park in the western Sierra Nevada mountains of California, carved out by the Merced River. The valley is about long and up to a mile deep, surrounded by high granite summits such as Half Dome and El Capitan, and densely forested with pines...
. As the hot magma cooled, solidified, and came in contact with water, minerals with similar melting temperatures tended to concentrate themselves together. As it solidified, gold became concentrated within the magma, and during this cooling process, veins of gold formed within fields of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
because of the similar melting temperatures of both.
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and crumbled, and the exposed gold and other materials were carried downstream by water. Because gold is denser than almost all other minerals, this process further concentrated the gold as it sank, and pockets of gold gathered in quiet gravel beds along the sides of old rivers and streams.
The California mountains rose and shifted several times within the last fifty million years, and each time, old streambeds moved and were dried out, leaving the deposits of gold resting within the ancient gravel beds where the gold had been collecting. Newer rivers and streams then developed, and some of these cut through the old channels, carrying the gold into still larger concentrations.
The Forty-Niners of the California Gold Rush
California Gold Rush
The California Gold Rush began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California. The first to hear confirmed information of the gold rush were the people in Oregon, the Sandwich Islands , and Latin America, who were the first to start flocking to...
first focused their efforts on these deposits of gold, which had been gathered in the gravel beds by hundreds of millions of years of geologic action.
Gold recovery
The early Forty-Niners panned for gold in California’s rivers and streams, or used "cradles" and "rockers" or "long-toms," forms of placer miningPlacer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....
. Modern estimates by the U.S. Geological Survey are that some 12 million ounces (373 t) of gold were removed in the first five years of the Gold Rush (worth approximately US$7.2 billion at November 2006 prices).
By 1853, the first hydraulic mining
Hydraulic mining
Hydraulic mining, or hydraulicking, is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment. In the placer mining of gold or tin, the resulting water-sediment slurry is directed through sluice boxes to remove the gold.-Precursor - ground...
was used. In hydraulic mining, (which was invented in California) a powerful stream of water is directed at gold-bearing gravel beds; the gravel and gold then pass over sluices, with the gold settling to the bottom. By the mid-1880s, it is estimated that 11 million ounces (342 t) of gold (worth approximately US$6.6 billion at November 2006 prices) had been recovered via "hydraulicking."
The final stage to recover loose gold was to prospect for gold in the flat rivers of California’s Central Valley
California Central Valley
California's Central Valley is a large, flat valley that dominates the central portion of California. It is home to California's most productive agricultural efforts. The valley stretches approximately from northwest to southeast inland and parallel to the Pacific Ocean coast. Its northern half is...
and other gold-bearing areas of California (such as Scott Valley
Scott Valley
Scott Valley is a large, scenic rural area of western Siskiyou County, California, known for its vistas of the Marble Mountains, cattle and dairy ranches, and its historic background as a gold mining area, dating back to the days of the California Gold Rush...
in Siskiyou County). By the late 1890s, dredging technology (which was also invented in California) had become economical, and it is estimated that more than 20 million ounces (622 t) were recovered by dredging (worth approximately US$12 billion at November 2006 prices).
Gold-seekers also engaged in "hard-rock" mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
, that is, extracting the gold directly from the rock that contained it (typically quartz) Once the gold-bearing rocks were brought to the surface, the rocks were crushed, and the gold was separated out (using moving water), or leached out, typically by using arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
or mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. Eventually, hard-rock mining wound up being the single largest source of gold produced in the Gold Country.
Geological after-effects
There were decades of minor earthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s, more than at any other time in the historical record for Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...
, before the 1906 San Francisco earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...
. Previously interpreted as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and due to large seasonal sediment loads in coastal bays that overlie faults as a result of mining of gold inland.