https://en.wikipedia.org/wiki/California_in_the_American_Civil_War

One of the earliest conflicts related to the Civil War in California occurred on November 29, 1861, at Minter Ranch, in the hills just south and west of the San Jose Valley, where Warner's Ranch and the military post of Camp Wright[21] was located. Dan Showalter's party of secessionists, like some others, were attempting to avoid the post and make their way across the desert to join the Confederate Army in Texas. They were pursued from Temecula by a Volunteer Cavalry patrol from the camp, intercepted and captured without shots being fired. Later after being imprisoned at Fort Yuma, Showalter and the others were released after swearing loyalty to the Union, but they made their way to the Confederacy later.[22]

New Camp Carleton was established on March 22, 1862, near El Monte; its garrison was to keep an eye on that hotbed of secessionist sympathies. On April 10, 1862, as the United States Marshal for Southern California, Henry D. Barrows, wrote to the commander of Union Army Department of the Pacific in San Francisco, complaining of anti-Union sentiment in Southern California. The letter says such sentiment "permeates society here among both the high and the low", and reports:

A. J. King, under-sheriff of this county, who has been a bitter secessionist, who said to me that he owed no allegiance to the United States Government; that Jeff Davis's was the only constitutional government we had, and that he remained here because he could do more harm to the enemies of that Government by staying here than going there; brought down on the Senator (a steam ship) Tuesday last a large lithograph gilt-framed portrait of Beauregard, the rebel general, which he flaunted before a large crowd at the hotel when he arrived. I induced Colonel Carleton to have him arrested as one of the many dangerous secessionists living in our midst, and to-day he was taken to Camp Drum. He was accompanied by General Volney E. Howard as counsel, and I have but little hope that he will be retained in custody.[23]

(http://www.autoadmit.com/thread.php?thread_id=5532959&forum_id=2#47693675)