The political situation in California was tense in 1846. Though nominally controlled by Mexico, California was home to only a relatively small number of Mexican settlers. Former citizens of the United States made up the largest segment of the California population, and their numbers were quickly growing. Mexican leaders worried that many American settlers were not truly interested in becoming Mexican subjects and would soon push for annexation of California to the United States. For their part, the Americans distrusted their Mexican leaders. When rumors of an impending war between the U.S. and Mexico reached California, many Americans feared the Mexicans might make a preemptive attack to forestall rebellion.
In the spring of 1846, the American army officer and explorer John C. Fremont arrived at Sutter's Fort (near modern-day Sacramento) with a small corps of soldiers. Whether or not Fremont had been specifically ordered to encourage an American rebellion is unclear. Ostensibly, Fremont and his men were in the area strictly for the purposes of making a scientific survey. The brash young officer, however, began to persuade a motley mix of American settlers and adventurers to form militias and prepare for a rebellion against Mexico.
Emboldened by Fremont's encouragement, on this day in 1846 a party of 33 Americans under the leadership of Ezekiel Merritt and William Ide invaded the largely defenseless Mexican outpost of Sonoma just north of San Francisco. Fremont and his soldiers did not participate, though he had given his tacit approval of the attack. Merritt and his men surrounded the home of the retired Mexican general, Mariano Vallejo, and informed him that he was a prisoner of war. Vallejo, who was actually a strong supporter of American annexation, was more puzzled than alarmed by the rebels. He invited Merritt and a few of the other men into his home to discuss the situation over brandy. After several hours passed, Ide went in and spoiled what had turned into pleasant chat by arresting Vallejo and his family.
Having won a bloodless victory at Sonoma, Merritt and Ide then proceeded to declare California an independent republic. With a cotton sheet and some red paint, they constructed a makeshift flag with a crude drawing of a grizzly bear, a lone red star (a reference to the earlier Lone Star Republic of Texas), and the words "California Republic" at the bottom. From then on, the independence movement was known as the Bear Flag Revolt.
After the rebels won a few minor skirmishes with Mexican forces, Fremont officially took command of the "Bear Flaggers" and occupied the unguarded presidio of San Francisco on July 1. Six days later, Fremont learned that American forces under Commodore John D. Sloat had taken Monterey without a fight and officially raised the American flag over California. Since the ultimate goal of the Bear Flaggers was to make California part of the U.S., they now saw little reason to preserve their "government." Three weeks after it had been proclaimed, the California Republic quietly faded away. Ironically, the Bear Flag itself proved far more enduring than the republic it represented: it became the official state flag when California joined the union in 1850.