Before the outbreak of the American Civil War, California's politics had been dominated by Southern Democrats. That changed, however, after the war started, except in Southern California. Southern California's population included a large number of white migrants from southern slave-owning states who naturally were sympathetic to the secession of their home states.
When war broke out, there was cheering and celebration in the streets of Los Angeles in favor of the secession. At the edge of the city was the sole U.S. military presence in Los Angeles - a single Army officer who oversaw the Los Angeles armory. Concerned that pro-confederacy sympathizers might attempt to seize his armory, he quickly fortified his post, called on local friends to arm themselves and join him, and sent an urgent plea for troop reinforcements. Within two months, reinforcements began arriving, culminating in a large presence of Federal troops in the Los Angeles area to discourage and suppress secessionist fervor (see Civil War Camps and Barracks in Los Angeles County).
There was every reason for the federal government to be concerned about pro-secessionist sentiment in Los Angeles County. It appeared that most county officials were openly pro-secession, including Los Angeles County Clerk John Shore, Los Angeles County Sheriff Tomas Avila Sanchez, his two undersheriffs, and a number of county judges. According to accounts of the time, the only county officials who were not secessionist were District Attorney Ezra Drown and County Surveyor William Moore. In March 1861, a month before Confederate forces opened the war by firing on Fort Sumter in South Carolina, a California militia in El Monte, the Los Angeles Mounted Rifles, declared themselves to be pro-secession. The militia was led by Los Angeles County Undersheriff Andrew King. His boss, Sheriff Sanchez, was listed among his troops, as was fellow undersheriff, Alonzo Ridley, and a number of deputy sheriffs. Federal authorities, however, saw to it that the militia remained unarmed and toothless, confiscating any arms provided to them. The Bella Union Hotel, then the finest hotel in Los Angeles, prominently featured a large portrait of Confederate Army General P.T. Beauregard in its lobby and served as a hub for the city's pro-secession crowd.
Shortly after President Abraham Lincoln issued the Emancipation Proclamation, ending slavery in the United States, L.A.’s leading newspaper, the pro-secession Los Angles Star, editorialized, on January 3, 1863:
“By the stroke of his pen, Mr. Lincoln frees every slave in rebeldom — robs every master of his servant, every household of its property. Was ever such an outrage perpetrated in the name of law, or such foul perjury committed, as by this man, sworn to maintain the Constitution and govern by the laws.”
See: Abraham Lincoln was not popular in Los Angeles County.
Pro-secessionist sentiment in Los Angeles was so prevalent, that July 4th Independence Day celebrations were cancelled in the city in 1863 and 1864.
Nevertheless, as federal authorities established a commanding presence in Los Angeles County, anyone openly declaring to be a secessionist was subject to arrest and offered the option of swearing an oath of allegiance to the United States or being charged with treason (and sent to Alcatraz Island). Even some of the county's most virulent pro-secessionists, including Sheriff Sanchez, former California Attorney General Edward Kewen, and Henry Hamilton, editor of the Los Angeles Star, opted for the oath of allegiance. An estimated 250 Southern Californians, however, chose to leave California and head east (threading their way through Apache territory and Federal patrols) to join with Confederate forces.
Even after the defeat of the Confederacy in 1865, some Angelenos continued to express defiance. Undersheriff King, the leader of the El Monte Rifles, declared after the war, “We have been and are yet secessionist.”
The struggle over slavery was not confined to the South, L.A. has a Confederate memorial problem too, by Kevin Waite, LA Times
'We Have Been and Are Yet Secessionist' – Los Angeles When the Civil War Began, by D.J. Waldie, KCET
What Happened in L.A. During the Civil War?, by Nathan Masters, KCET
Jan. 3, 1863: L.A. Paper Calls Lincoln’s Emancipation Proclamation an Outrage, by Larry Harnisch Reflects on L.A. History, LA Daily Mirror