As the United States grew in size, a flux of immigrants started to trickle into California from the East.
The governor granted a large piece of land near present-day Sacramento to a Swiss immigrant, John Sutter.
He instructed Sutter to build a fort to "prevent the robberies committed by adventurers from the United States, the invasion of savage Indians, and the hunting and trading by companies from the Columbia river".
Sutter named his settlement New Helvetia after his homeland (Helvetia = Switzerland). He had indeed fled debts to seek fortune in America, abandoning his wife and 5 children behind.
Far from "keeping the Americans out" however, Sutter provided them shelter as they arrived via the California trail.
His fort and the surrounding area became a major trade and agricultural hub, and can still be visited today.
Sutter's Fort provided shelter, supplies and guidance to people traveling on the Oregon and California Trails, which connected California to Missouri.
The Oregon Trail was used by about 400,000 settlers - mostly farmers, miners, ranchers, business owners and their families.
One of the toughest sections was crossing the Sierra Nevada, as evidenced by the Donner Party, who got stuck in winter and resorted to cannibalism.
Modern highways like the Interstates 80 and 84 follow parts of this trail.
Despite providing shelter to travellers, the fort was also a place of extreme brutality.
As in the missions, most of the labor was provided by Native Americans, many of whom were enslaved.
Shocked visitors to the fort described horrific brutality: children being separated from their mothers, raped, sold, or given as gifts to other settlers; workers being fed in troughs; sleeping in locked rooms with no sanitation; and being whipped, jailed, and executed.
Killing expeditions were also conducted to wipe out neighbouring Native American settlements.