The effects of the sudden migration to the West were spectacular. Before the gold rush, San Francisco was a tiny village, and with the fever the village became a city. Schools, roads and churches were built, and other towns were founded. A legal and governmental system was created, which led to the admission of California as a state of the Union in 1850. New means of transportation, such as the steamboat, entered service in the state, and railway lines were laid.

The gold rush also had other effects: the natives of the region were attacked and expelled from their traditional lands. Important was also the environmental impact that mining produced.

The human and environmental costs of the phenomenon were considerable. The native people of the region were victims of diseases, famines and genocidal attacks. The native population, estimated at 150,000 inhabitants in 1845, abruptly decreased to less than 30,000 people by 1870. The death toll among American immigrants was also severe, as one in every forty forty-niners perished; crime rates during the gold rush were extremely high, and the environment suffered considerable deterioration, thanks to gravel, loose soil, and toxic chemicals used in mining that killed animals and damaged habitats.