On January 24, 1848, gold was discovered in California. The word spread quickly, and Polk’s confirmation of the discovery in his last annual message, on December 5, 1848, turned gold fever into a worldwide epidemic. Word of limitless gold deposits in California, Polk said, “would scarcely command belief were they not corroborated by authentic reports.” Throughout the rest of the nation, men quit their jobs or sold their businesses and headed west in 1849 and after. These “Forty-niners” were often termed “Argonauts,” after the band of adventurers in Greek mythology who went in search of the Golden Fleece.

The California gold rush constituted the greatest mass migration in American history to that point. During 1848 some 80,000 gold seekers reached California, half of them Americans, and by 1854, the number would top 300,000. So many men left their families that people began to worry about the cohesion of society. The “Forty-niners” included people from every social class and from every state and territory, including slaves brought by their owners. Most went overland; the reset went by way of Panama or Cape Horn. Along the western slopes of the Sierra Nevada, they thronged the valleys and canyons.

After touring the gold region, the territorial governor reported that the influx of newcomers had “entire changed the character of Upper California.” The village of San Francisco, which grew rapidly into a city, mushroomed from 459 to 20,000 residents in a few months. The influx quickly reduced the 14,000 Mexicans in 1849 to a minority, and sporadic conflicts with the Indians of the Sierra Nevada foothills decimated the native peoples. In 1850 Americans accounted for 68 percent of the population, but there was also a cosmopolitan array of “Sydney Ducks” from Australia, “Kanakas” from Hawaii, “Limies” from London, “Paddies” from Ireland, “Coolies” from China, and “Keskydees” from France (who were always asking “Qu’est-ce qu’il dit?” – “What did he say?”).