California in the American Civil War was involved in sending gold east, recruiting volunteer soldiers to replace regular army forces in the Western United States and in maintaining and building numerous camps and fortifications. The State of California did not send its units east, but many citizens traveled east and joined the Union Army. California's Volunteers also conducted many operations against the Native American 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 were sympathetic to the Confederate States of America who seceded, but they were a minority group in the state. California businessmen played a significant role in Californian politics through their control of mines, shipping, finance, and the Republican Party. But they were a minority party until the secession crisis.

From statehood to the Civil War
When California was admitted as a state under the Compromise of 1850, Californians had already decided it was to be a free state. The constitutional convention of 1849 unanimously abolished slavery. As a result, Southerners in Congress voted against admission in 1850 while Northerners pushed it through, pointing to its population of 93,000 and its vast wealth in gold. Northern California, which was dominated by mining, shipping, and commercial elites of San Francisco, favored becoming a state. In the United States presidential election, 1856, California gave its electoral votes to the winner, James Buchanan.

Southern California's attempts at secession 
Following California's admission to the Union, Californios and pro-slavery Southerners in lightly populated, rural Southern California attempted three times in the 1850s to achieve a separate statehood or territorial status. The last attempt, the Pico Act of 1859, was passed by the California State Legislature. It was signed by the State governor John B. Weller and approved overwhelmingly by voters in the proposed Territory of Colorado. The proposal was sent to Washington, D.C. with a strong advocate in Senator Milton Latham. However the secession crisis following the election of Abraham Lincoln in 1860 led to the proposal never coming to a vote.

In 1860 Lincoln won 38,733 popular votes, only 32% of the total. But it was enough to win all four of California's electoral votes.

California volunteers called up 
On July 24, 1861, the Secretary of War called on the Governor of California for enlisted volunteer to guard the overland mail route from Carson City to Salt Lake City. They were also to guard Fort Laramie. The initial call was for five companies of cavalry plus one regiment of Infantry. On August 14,  four more regiments of infantry and one regiment of cavalry were requested. They were to report to General Edwin Vose Sumner. These volunteers replaced the regular troops transferred to the east before the end of 1861. California would have to protect itself using its own manpower during the Civil War.

The fight for California 
Both the Union and the Confederacy wanted California's gold. Ulysses S. Grant once said "I do not know what we would do in this great national emergency if it were not for the gold sent from California." The Confederates also needed ports that were not being blockaded by the Union Navy. If they could get control of Southern California it would give them the ports it badly needed. Southern California had a number of Southerners who moved to California during the Gold Rush. While they were a minority, they wanted Southern California to secede from the Union and join the Confederate states. At the time, Northern California was very pro-Union. A number of pro-Confederate groups were organized in Southern California. These included the Los Angeles Mounted Rifles and chapters of the Knights of the Golden Circle, a secret pro-slavery organization.

The pro-Union state militias and Union forces used a number of forts and camps in California. One of the best known is Alcatraz Island. Before it was a federal prison, it was a prisoner of war camp for Confederate prisoners. The last army fort still standing is the Drum Barracks. It was the headquarters of the Union Army in Southern California and the Arizona Territory.

References 

 
19th century in California