The statement is false, as the California gold rush was bad for the environment.
The human and environmental costs of the phenomenon were considerable. The native people of the region were victims of diseases, famines and attacks. The native population, estimated at 150,000 inhabitants in 1845, abruptly decreased to less than 30,000 people by 1870. Explicitly xenophobic laws were enacted, seeking to alienate immigrants from China and Latin America. The death toll among American immigrants was also severe, as one in every twelve 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.
However, the gold rush catapulted California into the center of the global imagination, making it the destination of hundreds of thousands of people, who often displayed remarkable inventiveness, autonomy and civility. In this period, towns and cities were founded; A constituent assembly was also convened, which drafted the state Constitution. Elections were held, and representatives went to Washington to negotiate the admission of California as a state of the Union.