Gold became highly concentrated in California, United States 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.

Some 400 million years ago, rocks that would be accreted onto western North America to build California lay at the bottom of a large sea.

[2] Beginning about 200 million years ago, tectonic pressure forced the sea floor beneath the American continental mass.

[3] As it sank, or subducted, beneath the western margin of the North American plate portions of the sea floor and overlying continental crust heated and melted, producing 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[4] to become the granite rock found throughout the Sierra Nevada and other mountains in California today.

[4][6] 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 subjected to erosion.

[18] In a modern style of hydraulic mining first developed in California, a high-pressure hose directed a powerful stream or jet of water at gold-bearing gravel beds.

[20] As of 1999[update] many areas still bear the scars of hydraulic mining, since the resulting exposed earth and downstream gravel deposits do not support plant life.