As a matter of fact, in President Polk´s Annual Message to U.S. Congress, he wrote:
“It was known that mines of the precious metals existed to a considerable extent in California at the time of its acquisition . Recent discoveries render it probable that these mines are more extensive and valuable than was anticipated. The accounts of the abundance of gold in that territory are of such an extraordinary character as would scarcely command belief were they not corroborated by the authentic reports of officers in the public service who have visited the mineral district and derived the facts which they detail from personal observation.”
A typical ’49er, panning for gold in California
The Gold Rush was a social phenomenon occurred in the US between 1848 and 1855, characterized by the large number of immigrants who arrived in the vicinity of San Francisco (California) in search of that metal. This phenomenon began near the town of Coloma, when gold was discovered at Sutter's Mill.
When news of the discovery spread, about three hundred thousand people immigrated to California from the rest of the United States, Australia, and other countries mainly from Asia, Europe and Latin America.