The California War (1846 – 1848)


Anytime someone mentions the Mexican-American War (1846 – 1848), what comes to mind to most people are the battles that took place inside Mexico.  Everyone is thinking, “Mexico.”  They don’t think about California — but California was a province of Mexico, and everyone living in Mexico in 1846 was either a citizen of Mexico, a visitor, or perhaps even an illegal alien.

I suspect that no Mexican official was surprised when the United States annexed the Republic of Texas in December 1845.  Mexican officials had suspected the Americans of perfidy before Mexico’s War of Independence (1810 – 1821).  A warning flag went up when the United States purchased the Louisiana Territory from France (1803), who had assured Spain that France would not sell the territory to the Americans.  Mexican officials weren’t duped, however.  They knew, as well as anyone, that Mexico’s northern territories were an unmitigated disaster (and had been for three hundred years), and they knew that their decision to populate the territories of the north with Anglo settlers was — at best — a hazardous venture.

Still, the Texas Revolution was avoidable even in 1835.  The majority of Mexico’s state and territorial governors supported the Constitution of 1824 — as did the Anglo citizens of Texas y Coahuila.  It wasn’t until President Antonio de López de Santa Anna suspended the Constitution of 1824 that the dirt hit the fan.  Nor was Texas the only state or province in rebellion.  Although it would be less than honest in this discussion to ignore Texians who were not only hoping for an independence movement, but there were others, too, who (always) wanted Texas for the United States — notably, Texian General Sam Houston (a former Governor of Tennessee), and U.S. President James K. Polk (also a former governor of Tennessee).

The word is — untrustworthy

Mexican officials also knew that the Americans had designs on California.  President Polk made no qualms about his expansionist policies, and few in the Congress of the United States were ready to believe Polk’s explanation for his request for a declaration of war against Mexico.  Two prominent members of Congress who thought President Polk guilty of lying were former President John Quincy Adams and a freshman representative from Illinois named Abraham Lincoln.  But Polk had his supporters, too — far more support than dissent.  In 1846, Walt Whitman said, “What has miserable, inefficient Mexico — with her superstition, her burlesque upon freedom, her actual tyranny by the few over the many — what has she to do with the great mission of peopling the new world with a noble race?  Be it ours to achieve that mission!”

Noted historian and author Theodore R. Fehrenbach (d. 2013) insisted that the Mexican War was a presidential war of dominant administration policies, carried out for strategic reasons against the wishes of a considerable anti-war opinion.  The Mexican War, he insists, was “tremendously successful” for two reasons.  First, American arms were surprisingly and quickly victorious, and the seemingly immense goals were limited to acquiring (useless or under-utilized) Mexican territory.  Plus, the American army was withdrawn before the citizens could rise against it.

The fact is that the United States never wanted to own or control Mexico.  It intended to subordinate Mexico to the United States.  The war permanently removed Mexico as a rival for the North American continent.  In this sense, 1848 was remarkable because it was the first time the United States was strategically secure.[1]  

In any case, President Polk had previously dispatched Captain John C. Fremont to California, ostensibly to survey the Great Basin watershed in 1845, and wasted no time ordering General Stephen W. Kearney to seize New Mexico.  For his part, American Consul (Monterrey) Thomas O. Larkin worked hard to avoid conflict in California with General José Castro, Mexico’s senior-most official.[2]

Word of the United States’ declaration of war reached California by August 1846.  Larkin’s primary task was to avoid bloodshed between Americans in California and the Mexican military garrison.  Mexican General José Castro was not a happy man in the summer of 1846.  At the time of the outbreak of war, Captain Fremont (and his party) were at Klamath Lake (Oregon Territory) — he wasted no time relocating his expedition of map-makers to Sacramento.

Defending the homeland

Meanwhile, the government of Mexico proclaimed that all unnaturalized foreigners were no longer permitted to own land in California and were subject to expulsion.  The announcement generated rumors that Castro was massing an army to expel all American settlers in the Sacramento Valley.  The settlers banded together to meet that threat.  On 14 June, 34 Americans seized control of the undefended Mexican (government) outpost at Sonoma.  They did it to “forestall” General Castro’s plans.  One settler created the Bear Flag and raised it over Sonoma Plaza.  Within a week, 70 more volunteers joined the rebel force, which before July 1846, had grown to a strength of 300 men.  The leader of this “Bear Flag Revolt) was William B. Ide.[3]

On 25 June, Fremont and his party arrived to assist in any military confrontation.  The Bear Flag group “occupied” Yerba Buena (San Francisco) on 2 July, and a few days later, Fremont organized his “California Battalion” by organizing the American settlers (the rebels).

U.S. Navy Commodore John D. Sloat, commanding the Pacific Squadron, was positioned off Mazatlán, Mexico, when he received orders to seize San Francisco Bay and blockade Californian ports once he was “positive that war had begun.”[4]  Mindful that the British also had designs on California, Commodore Sloat wasted no time setting sail for Monterey, arriving on 1 July.  Upon learning of the events in Sonoma, and Fremont’s involvement, Sloat erroneously believed that Fremont was acting on orders from Washington.  On 7 July, Sloat ordered his Marines to prepare to land and seize the Mexican Customs House at Monterey.  The landing occurred on 9 July, and the U.S. flag was raised to signify America’s seizure of California.  On Sloat’s orders, Captain Fremont brought 160 volunteers and the so-called California Battalion to Monterey to reinforce his Marines and naval infantry.  On 15 July, Sloat relinquished his command to Commodore Robert F. Stockton, U. S. Navy 

For the next twenty-two days, Sloat served as military governor of California, later relinquishing his office to Commodore Robert F. Stockton, U. S. Navy.  Sloat’s relief from command resulted from his illness, which made him lethargic.  Stockton, a more aggressive officer, mustered willing members of the California Battalion into military service, appointing Captain Fremont as the battalion commander.  He ordered Fremont to San Diego to prepare for operations in Los Angeles.  At the same time Fremont’s battalion landed in San Pedro (a coastal region of Los Angeles), Stockton’s 360-man force also landed.  Mexican governor Pico Pio and General Castro wrote farewells to their constituents and fled to Sonora, Mexico.

Commodore Stockton entered Los Angeles unopposed on 13 August.  He sent a report to the U.S. Secretary of State reporting that California was free from Mexican Dominion.  His message was premature, for in leaving a small force behind, he invited the intervention of insurrectionists known as Californios.  One such man was José Maria Flores, who forced the withdrawal of American garrisons in San Diego and Santa Barbara.  When Captain William Mervine landed 350 Marines and sailors at San Pedro on 7 October, José Flores ambushed and repulsed them.[5]

Having little knowledge of the enemy, Mervine embarked upon a poorly planned force march into Los Angeles.  The operation began inauspiciously with the death of a cabin boy by friendly fire.  His troops were armed with various weapons, requiring different munitions and a wide selection of cutlasses and pikes.  They brought no horses, wagons, or field cannons.  The initial march was a six-hour slog over dusty roads without access to fresh water.  Moreover, Forces under José Flores harassed them through intermittent gunfire.

Mervine and his men reached the abandoned Dominguez Ranch and camped for the night.  Gunfire throughout the night had little effect other than to deny Mervine’s force of a good night’s sleep.

As Americans occupied Los Angeles the previous August, Mexican residents had hidden some weapons by burying them.  General José Flores was also poorly equipped at the time, but he had access to a cannon.  It was an old brass four-pounder used in the Los Angeles Plaza for ceremonial purposes.  The gun was one of the weapons buried by Clara Cota de Reyes (aided by her daughters).

Flores dug up the cannon, mounted it on a horse-drawn limber, and placed it on the narrow trail the Americans would use in their approach.  The simple tactics proved effective.  Californio horsemen deployed at a safe distance from the path on the American’s flanks.  When the Americans came within 360 meters, the cannon was fired and quickly pulled back into the brush, followed by musket fire from the horsemen on the American’s flanks.  Realizing they could not reach Los Angeles, Captain Mervine had little choice except retreat.  The main battle lasted less than one hour; five hours later, Mervine’s force was back aboard ship in San Pedro Bay.  The Mexicans called this dustup the Battle of the Old Woman’s Gun.

Meanwhile, General Kearney (at the head of 115 men) completed a grueling march across the Sonoran Desert and crossed the Colorado River in late November 1846.  Stockton sent a 35-man patrol from San Diego to meet the Kearney group.  On 7 December, General Andres Pico (brother of California’s last Mexican governor), with 100 mounted lancers, lay in wait near San Pasqual.  Kearney lost three officers and 22 men in a fight lasting 30 minutes.  Kearney pushed on to Mule Hill, where he formed a defensive perimeter and waited out a siege lasting four days.

Fremont, leading 428 men, traveled to San Luis Obispo and Santa Barbara.  By 28 December, Kearney (now leading a force of around 600 men, began a 150-mile march to Los Angeles.  Flores decided to assault Kearney by moving his ill-equipped 500-man force to a bluff above the San Gabriel River.  The Americans defeated Flores in a battle lasting two hours.  Another battle followed the next day, 9 January 1847, at La Mesa.  The U.S. Army entered Los Angeles on 10 January with no opposition.  Armed resistance in California ended on 12 January when Fremont and two of General Pico’s officers agreed to terms of surrender.

The Pacific Coast Campaign

In the fall of 1847, United States warships Independence, Congress, and Cyane entered the Gulf of California to seize La Paz.  The ships afterward burned the small Mexican fleet of vessels at Guaymas and, within a month, cleared the gulf of hostile ships, destroying or capturing thirty ships.  Later, sailors and Marines captured Mazatlán, and once upper California was secure, most of the squadron proceeded down the California coast, capturing Baja California and capturing or destroying nearly all Mexican vessels operating in the Gulf of California.

It is clear that the Americans had their designs on Baja California — and would have seized it as well, were it not for the efforts of an Army officer named Manuel Pineda Muñoz.  We do not know this officer’s military rank, but we credit him with organizing a campaign of resistance that prevented Baja California from falling into the hands of President Polk and his California forces.  Muñoz retook several ports captured by the Americans, which he ultimately lost again.  Still, because of the timing of this conflict, the issue of Baja California as a territorial acquisition never made it into discussions leading to the Treaty of Guadalupe Hidalgo.  When the war was over, many Mexicans who aligned with the American cause traveled to Upper California, where they settled permanently.


  1. Eisenhower, J.  So Far from God: The U.S. War with Mexico.  Random House, 1989.
  2. Fehrenbach, T.R.  Lone Star: A History of Texas and Texans.  Open Road Publishing, 2014.
  3. Fowler, W.  Santa Anna of Mexico.  Bison Books, 2009.
  4. Haas, L.  Conquests and Historical Identities in California, 1769-1936.  University of California Press, 1995.
  5. McCaffrey, J. M.  Army of Manifest Destiny: The American Soldier in the Mexican War: 1846-1848.  NYU Press, 1994.


[1] The last great surge of Jacksonian Democrats occurred between 1844-1848; the Democratic Party was soon after destroyed by sectionalism — and its supporters (Polk, Houston, Benton) were destroyed with it.  Jacksonian Democrats had their own point of view, of course.  They saw themselves as westerners who were suspicious of easterners, but above all that they had a somewhat mystical view of the growth of the United States: it was a country grown so great that even fools could not destroy it.  To Jacksonians, slavery was only a tool used to solidify their political base — and nothing was as important to them as territorial expansion.

[2] The Great Basin is the largest area of contiguous endorheic watersheds in North America, spanning nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California.

[3] Ide was born and raised in Massachusetts.  He was a carpenter by trade and at one time served as a representative in the Vermont legislature.  He and his wife began their “westward” movement around 1830 with stops in Kentucky, Ohio, and Illinois.

[4] The Navy appointed Sloat to command the Pacific Squadron in 1844.  As tensions increased with Mexico in 1845, the Navy instructed him to land in Alta California, and, should war break out, claim California in the name of the United States. 

[5] In 1847, William Mervine (ultimately a Rear Admiral) commanded USS Savannah.  In this capacity, he commanded a force of 203 Marines and 147 U.S. sailors, and a number of civilian volunteers in the invasion of Los Angeles.   

About Mustang

Retired Marine, historian, writer.
This entry was posted in FRONTIER, HISTORY, LONE STAR, MILITARY. Bookmark the permalink.

1 Response to The California War (1846 – 1848)

  1. Andy says:

    Mexico had treated the Texans as ugly stepchildren. It was no wonder Texas wanted to break away from the motherland. It was a long and at times desperate fight, but now Texas is where, and with whom, it was always meant to be.

    Liked by 1 person

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