Until the middle of the nineteenth century, settlement of America’s western frontier generally reached no farther than the Great Plains. The verdant land that Spanish conquistadors called Alta California had been claimed by Spain and then by Mexico, after it secured its independence, in 1821. In 1844, James K. Polk won the Presidency as a proponent of America’s “manifest destiny,” the belief that it was God’s will for the United States to extend from the Atlantic Ocean to the Pacific, and soon took the country into a war with Mexico. Under the Treaty of Guadalupe Hidalgo, in 1848, Mexico ceded California to the United States, along with the vast expanse of land that today comprises Nevada, parts of Arizona, and New Mexico.

California was sparsely populated and almost wholly separate from the rest of the country. Sailing there from the Eastern Seaboard, around South America, could take six months, and the overland journey was even more arduous. The fledgling town of San Francisco consisted of a collection of wood-frame and adobe buildings, connected by dirt paths, spread out on a series of slopes. Fewer than a thousand hardy inhabitants, many of them Mormons fleeing religious persecution, occupied the sandy, windswept settlement.

That changed with remarkable suddenness. On the morning of January 24, 1848, James W. Marshall was inspecting progress on the construction of a sawmill on the banks of the American River, in the foothills of the Sierra Nevada mountains, about a hundred and thirty miles northeast of San Francisco. In his recounting, he spotted some glints in the water and picked up one or two metallic fragments. After studying them closely, he realized that they might be gold. Several days later, he returned to New Helvetia, a remote outpost in the Sacramento Valley, where he asked his business partner, John Sutter, to meet with him alone. The two men conducted a test with nitric acid and satisfied themselves that the find was genuine. Sutter implored those working the mill to keep quiet about the discovery, but, in May, 1848, a Mormon leader who owned a general store at the outpost travelled to San Francisco and heralded stunning news. “Gold! Gold! Gold from the American River!” he reportedly shouted as he strode through the streets, holding aloft a bottle full of gold dust and waving his hat. Within a few weeks, most of San Francisco’s male population had decamped for the hills. The town’s harbor was soon filled with abandoned ships whose crews had rushed off in search of wealth.

It is uncertain exactly how word of the gold rush reached China. According to one account, a visiting merchant from Guangdong Province named Chum Ming was among the many men who ventured into the Sierra Nevada foothills and struck it rich. As the story goes, Chum Ming wrote to a friend back home, and the news began to circulate. Mae Ngai, a professor of Asian American studies at Columbia University, begins her book “The Chinese Question” (Norton) with a more verifiable fact: the arrival of a ship carrying California gold––specifically, two and a half cups of gold dust––in Hong Kong on Christmas Day, 1848. A San Francisco agent of the Hudson’s Bay Company, the fur-trading concern, had requested that British experts in China evaluate it. The ship also brought copies of the Polynesian, a Honolulu newspaper, which reported on the immense quantities of gold being extracted by prospectors in California.

Soon, word spread through villages across the Pearl River Delta, a populous area in southeastern China. At the time, it was illegal for Chinese citizens to leave the country, and Qing-dynasty officials offered little protection for emigrants. Nevertheless, men throughout the region began booking passage on ships bound for Gum Shan—Gold Mountain. Ngai writes that they were just like other gold seekers from around the world: farmers, artisans, and merchants, who mostly paid their own way or borrowed money for the voyage to America. The trip across the ocean was frequently a miserable experience. It generally took ten to twelve weeks to sail from Hong Kong to San Francisco. Shipmasters often stuffed the men into overcrowded, poorly ventilated, disease-ridden holds. One ship arrived in San Francisco harbor having lost a hundred Chinese en route, a fifth of those on board. “There can be no excuse before God or man for the terrible mortality which has occurred on some of the vessels containing Chinese passengers,” William Speer, a Presbyterian missionary who treated many Chinese after they disembarked in San Francisco, wrote.

In 1849, three hundred and twenty-five Chinese passed through San Francisco’s customhouse. The next year, the number increased to four hundred and fifty; the year after that, it was twenty-seven hundred. In 1852, the arrivals jumped to more than twenty thousand. By the late eighteen-fifties, Chinese immigrants made up about ten per cent of the state’s population, and even more in mining districts. California, teeming with white Americans, Native people, Mexicans, Blacks, Chinese, Irish, Germans, Frenchmen, Hawaiians, and others, had become the substrate for a nettlesome experiment in multiracial democracy that had little precedent in the country’s history.