On January 24, 1848, a thin piece of metal the size and thickness of a corn flake altered the history of California and, by extension, the history of the United States.

That day, in a remote region of the Sierra Nevada foothills, a man named James Marshall was overseeing the construction of a sawmill on the American River. He was building the mill for his boss, John Sutter. As he looked in the millrace, a fast moving stream that powered the mill wheel, Marshall spotted a glint of color. After picking up the flake and applying rudimentary tests to the metal, Marshall came to a conclusion: he had discovered gold!

San Francisco Empties Out

Four days later, Marshall informed Sutter, who urged him to keep the discovery secret so that work on the sawmill would be completed. Eventually, word of the gold spread across the region like a Western wildfire, igniting the curiosities of the citizens of the nearby city of San Francisco.

By the spring of 1848, people poured out of San Francisco hoping to strike it rich. It is said that San Francisco emptied after businessman Sam Brannan walked down the city’s Montgomery Street with a bottle containing gold flakes, grains, and dust, shouting: “Gold! Gold! Gold from the American River!”

An historian and author of 1997’s Days of Gold: The California Gold Rush and the American Nation, Malcolm J. Rohrbough says the immediate effects of the discovery of gold on San Francisco were nothing short of drastic.

“The whole town and the rancheros around the town essentially were deserted,” he says. “Everyone went to the gold fields.”

The summer after Marshall’s unexpected find, the American military governor of California, Colonel Richard Barnes Mason, decided to travel to the area to draft a report for the U.S. government in Washington D.C. On his journey to the region, he described finding parts of California towns that were suddenly abandoned by people fleeing to the Sierra Nevada foothills.

Mason wrote in the letter that he saw “whole route mills were lying idle, fields of wheat were open to cattle and horses, houses vacant and farms going to waste.”

But when Mason arrived at the gold fields, he discovered swarms of people sifting through the streams and dirt in a mad search for gold. “At the time of my visit, but little more than three months after its first discovery, it was estimated that upwards of 4,000 people were employed [in the gold fields],” Mason wrote in the letter.

Near the end of the report, Mason described how abundant the precious metal was and how it could be easily extracted from the land. “I have no hesitation now in saying, that there is more gold in the country drained by the Sacramento and San Joaquin Rivers than will pay the cost of the present war with Mexico a hundred times over,” he wrote. “No capital is required to obtain this gold, as the laboring man wants nothing but his pick and shovel and tin pan, with which to dig and wash gravel, and many frequently pick gold out of the crevices of rocks with their knives, in pieces of one to six ounces.”

From Mexico to the United States

The years before Marshall’s big discovery, California had been a northern frontier of Mexico. Less than two weeks after gold was found, California was given to the United States by Mexico through the Treaty of Guadalupe Hidalgo, which ended the Mexican-American War.

“Politically, California in many respects was independent or quasi-independent,” Rohrbough says of pre-Gold Rush California. “Economically, it was very much connected to the hides [pelts or animal skins] and tallow [the fatty tissue of animals] trade.”

California’s population and diversity would change drastically once Mason’s letter arrived on the East Coast. The initial reports of gold were greeted with skepticism, according to Rohrbough. However, everything changed when President James K. Polk gave his State of the Union address to Congress on December 5, 1848. Of the gold craze in California, the President stated: “the explorations already made warrant the belief that the supply is very large and that gold is found at various places in an extensive district of country.”

Following the President’s confirmation of the rumor, a gold mania swept across the United States.

In mid to late December, ships filled with gold-seekers left the East Coast for California. During the spring of 1849, scores of people embarked on a journey across the continent hoping to find gold. In reference to the year of their departure, these early immigrants to California were called forty-niners.

Rohrbough cites the number of miners in California in 1848 compared to populations over the following years as proof of the amazing movement of gold-seekers to the newly acquired American territory. He says that in 1848 there were 5,000 miners in the region. There were more than 50,000 by the end of 1849. The number rose to 100,000 in 1850 before peaking at 125,000 in 1851.

While gold miners came from as far away as Europe and China, the California Gold Rush drew many young men from their homes in the American Midwest and East Coast. That flood of Americans radically changed California during the Gold Rush years.

“California was Americanized, almost literally, overnight,” Rohrbough says, “and became a place that was dominated by Americans as opposed to the Mexicans who were so prominent at the time of the gold discoveries.”