California in the American Civil War

California's involvement in the American Civil War included sending gold east, recruiting volunteer combat units to replace regular forces in territories of the Western United States, maintaining and building numerous camps and fortifications, suppressing secessionist activity (many of these secessionists went east to fight for the Confederacy) and securing the New Mexico Territory against the Confederacy. The State of California did not send its units east, but many citizens traveled east and joined the Union Army and there, some of whom became famous. California's Volunteers also conducted many operations against the native peoples within the state and in the other Western territories of the Departments of the Pacific and New Mexico.

Following the Gold Rush, California was settled primarily by Midwestern and Southern farmers, miners and businessmen. Democrats dominated the state from its foundation. Southern Democrats sympathetic to secession, although a minority in the state, were a majority in Southern California and Tulare County, and were in large numbers in San Joaquin, Santa Clara, Monterey, and San Francisco counties. California was home for powerful businessmen who played a significant role in Californian politics through their control of mines, shipping, finance, and the Republican Party but were a minority party until the secession crisis.

In 1860, as tensions escalated in the East, pro-Union Californians protested the perceived pro-Southern bias of the San Francisco Roman Catholic archdiocese's weekly newspaper, The Monitor, by dumping its presses into San Francisco Bay. In the beginning of 1861, as the secession crisis began, the secessionists in San Francisco made an attempt to separate the state and Oregon from the union, which failed. Southern California, with a majority of discontented Californios and Southern secessionists, had already voted for a separate Territorial government and formed militia units, but were kept from secession after Fort Sumter by Federal troops drawn from the frontier forts of the District of Oregon and District of California (primarily Fort Tejon and Fort Mojave).

...
Wikipedia