The first California Volunteer Militia was organized by, the man historical writings refer to as "The Pathfinder. This same individual later became one of the State's first Senators and was appointed a Major General in the Union Army during the Civil War.
This man was Captain John Charles Fremont, U.S. Army topographer, explorer, and trail blazer. Captain Fremont began his treks westward into United States trerritory and beyond in 1842. It was during his third expedition (1845-1846) that he assisted in turning the course of history in California.
In December 1845, Captain Fremont, and a force of sixty men, entered into the Mexican province of Alta California ostensibly to map the west coast area. Although he officially made contact with Mexican authorities, his movements around the province was a point of consternation to Mexico's Northern Regional Commander, General Jose Castro. In particular, the latter did not care for Fremont's contact and sympathy for American settlers and emigrants.
The Fremont Party having traversed the territory as far north as Klamath on the California/Oregon border, turned south upon hearing that a proclamation had been issued by General Castro, aimed at driving out foreigners from the province. Fremont, though sympathetic could not commit U.S. Forces to aid the settlers. Nevertheless, he did decide to stay and advise those who chose to confront the Mexican authorities. Captain Fremont established his base camp at the base of four buttes (Sutter Buttes) in the Sacramento Valley a few miles north of John Sutter's Fort.
Word of the camp reached a group of settlers who were most vociferous in their dislike of the province's government. Leader of this group calling themselves Osos (Spanish for Bears), was Ezekiel "Stuttering" Merritt. Merritt was well known in the territory, and the west, for having been a fur trapper in the Rocky Mountains. Captain Fremont gladly accepted the twenty Osos, and went so far as to appoint Zeke Merritt a lieutenant of the irregulars.
Fremont remained in the background of events, not wishing to involve the United States in any altercations the Osos might be involved in; however, he and his force had already been branded "bandits" by General Castro, after an alleged horse stealing episode near Salinas during May 1846. Hence, in early June, Captain Fremont gave advice to capture the Northern Headquarters of General Mariano Vallejo at Sonoma. On June 14, the Osos took the town of Sonoma in the early dawn light without firing a shot. And with the acceptance of General Vallejo's surrender the Osos declared California a Republic, and raised the Bear Flag over the plaza.
Captain Fremont saluted the Bear Flaggers, whose force now numbered ninety, when both the flag of the United States and California Republic were raised on July 4, 1846, in celebration of United States and California Independence.
Following the celebration, Captain Fremont proposed that a unified force be organized, under his command. A discussion was held July 5, with William Brown Ide (Grigsby-Ide emigrant party of 1845), who the Bear Flaggers had elected as their Commander-in-Chief. A compact was drawn up for all volunteers to sign, which in part read: Not to violate the chastity of Women; conduct their revolution honorably; and pledge obedience to their officers. With the signatures or marks of the men, the California Battalion was formed. Fremont appointed a Marine Corps Officer, Captain Archibald H. Gillespie, his Adjutant. Captain Gillespie had joined Fremont when the latter was at the Oregon Border. Gillespie had crossed the Mexican nation and entered California about the time hostilities broke out with the opening of the Mexican War, May 1846. Fremont requested the Battalion's volunteers to elect their officers from the ranks. Chosen were: Richard Owens, John Grigsby, Granville P. Swift, and Henry L. Ford.
The California Battalion was given further legitimacy when on July 23, it was recognized by the American military leader in California, Commodore Robert Field Stockton, Commander of U.S. Naval Forces in the Pacific. J.C. Fremont was promoted to Major by Commodore Stockton, and given command of all Volunteer Militia. Major Fremont and the California Battalion eventually came under the command of Brigadier General Stephen Watt Kearney. Following this command change the Battalion came into prominence when in January 1847 they accepted the surrender of the Californios, thereby ending the conflict in California.