Prior to the Mexican–American War the Californio forces had routed the Mexican-appointed Governor Manuel Micheltorena and most of his forces from Alta California. The Californio Governor Pio Pico, had about 100 poorly armed and poorly equipped soldiers, and was nominally in charge in Alta California; he consolidated his forces in Pueblo de Los Angeles—the then-largest city in California with about 1,500 residents. The main forces available to the United States in California were the about 400–500 bluejacket sailors and U.S. Marines on board the five ships of the Pacific Squadron there. Speculating that war with Mexico over Texas etc. was very possible, the U.S. Navy had sent several additional naval vessels to the Pacific in 1845 and 1846 to protect U.S. interests there and prevent possible British action. It took about 200 days, on average, for ships to travel the over- trip from the East coast around Cape Horn to get to California. More ships assigned to the Pacific Squadron would continue to arrive from 1846 to 1847. On 26 May, Commodore Sloat received word of the Battle of Palo Alto and the Battle of Resaca de la Palma, upon which he sent a coded message to Secretary of the NavyGeorge Bancroft that he was leaving for California. Sloat sailed on the frigateSavannah on 8 June, arriving at Monterey on 1 July. They joined the sloop which was already there. There were U.S. fears that the British might try to annex California to satisfy British creditors. The British Pacific Station's ships off California were stronger in ships, guns and men. On 6 July, Sloat decided to seize Monterey and San Francisco, wondering if "Captain Freemont will cooperate with us."
Battle
Capt. William Mervine of the Cyane came ashore with a small party from the Savannah at 7:30 AM on 7 July, seeking the surrender of the port from the Mexican commandant, Capt. Mariano Silva. Silva replied that he was "not authorized to surrender the place." In fact, Silva was in command of a nonexistent garrison. The Californio soldiers had already left the town's defenses and gone to Los Angeles. They would have had no gunpowder to use in their few cannons even if they had stayed. At 10 a.m., 225 sailors and marines from Sloat's three warships landed. They formed before the Customs House where Purser Rodman M. Price read Sloat's proclamation of a state of war between the US and Mexico and the annexation of California by the US. The only shots fired were a 21-gun salute to the new US flag fired by each of the US Navy ships in the harbor. The British ships observed but took no action.
Aftermath
Sloat recognized Mexican real estate titles and church lands. He also established justices of the peace when the alcaldes resigned his office. Capt. John B. Montgomery of the Portsmouth received Sloat's message to seize Yerba Buena and by 8 AM on 9 July, read the pronouncement at the Customs House. He then replaced the Bear Flag with the American flag. The American flag was run up with a 21-gun salute. Montgomery then sent Purser James H. Watmough to notify Fremont at Sonoma and Sutter's Fort. Commodore Robert F. Stockton arrived at Monterey Bay aboard the Congress on 15 July and took over command from Sloat. The British ship of the lineCollingwood arrived in Monterey on 23 July, and Juno arrived at Yerba Buena on 11 July, but neither ship interfered in the American activities. The Bear Flag revolutionaries were soon combined with John C. Frémont's 60 man exploratory force to form the U.S. sponsored California Battalion under the command of Frémont. The California Battalion, which varied from 160 to 400 men, drew regular army wages and were used to garrison and maintain order in the towns that had surrendered. The Americans held northern California but General Jose Maria Castro and Governor Pio Pico planned resistance in the south.
