On January 8, 1847, about 500 Mexican militia, commanded by the young General José María Flores (only about 28 years old, but appointed general because he was the only remaining professional military officer), hastily set up defenses on a bluff overlooking the San Gabriel River (in modern-day Montebello). The incident would become known as the Battle of the San Gabriel River. Flores' command was the last significant Mexican military force able to offer any resistance to a military invasion of Alta California by U.S. forces. The Mexicans (or Californios, as they preferred to call themselves) faced a force of about 600 U.S. troops, advancing from San Diego. The American formation was composed of marines, sailors, army dragoons and California volunteers, commanded by U.S. Navy Commodore Robert F. Stockton and, secondarily, U.S. Army General Stephen Watts Kearny. A month earlier, Flores' deputy, Andres Pico, leading a reconnaisance cavalry force south of Los Angeles, successfully engaged with Kearny's “dragoons” (mounted infantry) at San Pasqual (in modern-day San Diego County). Although outgunned, Pico inflicted serious casualties on the Americans (18 killed) and forced the badly-mauled Americans to retreat to San Diego. Kearny himself suffered several lance wounds. The Americans, however, on this January morning, now approached with a larger, better prepared and better armed force. The Californio force was mostly composed of inexperienced and poorly-equipped militia and local citizen volunteers.
The entrenched Californios opened fire on the advancing American force, as the Americans marched up to the riverbank in the open to cross the San Gabriel River. What followed were two hours of artillery exchanges and unsuccessful Californio cavalry charges (Californio cavalry, armed mostly with lances, had little success at penetrating withering American firepower). Flores concluded that he could not force the Americans to withdraw, much less defeat them in any counter-attack. He ordered an orderly withdrawal, before his troops could be overwhelmed or set into a panicked retreat. Upon determinng that the Californios had withdrawn, the Americans followed by occupying the vacated bluff, seizing abandoned Mexican artillery, and setting up camp for the day.
By the following day, January 9th, unfortunately for the Mexican defense, many Californio volunteers had concluded that the fight was futile and elected to simply give up and return to their homes. Flores could do little to stop them. Even with a now hugely diminished force, Flores attempted a desperate re-engagement with the advancing Americans at the Battle of La Mesa (in modern-day Vernon). His determined horsemen offered a more intense and more mobile fight than in the day before, even almost completely "enveloping" the American force. Yet, the Californios lacked the numbers and firepower to break through the American defensive lines. Flores, seeing that he had nothing left with which to stop the Americans, ordered a final withdrawal. Civilian leaders from Los Angeles, then seeing no further hope of keeping the American force at bay, offered to surrender the city peacefully.
On January 10th, the American force occupied Los Angeles. Flores' remaining troops retreated to a camp outside of Los Angeles. He knew that yet another American force, commanded by U.S. Army Lieutenant-Colonel John C. Fremont, was marching from the north to meet up with Stockton and Kearny in Los Angeles. In fact, Fremont had, by this time, already arrived at the Mission San Fernando. Flores, still in command of the tiny remnant of Mexican California's force, seeing any further resistance as futile, dismissed suggestions of partisan warfare. He was also aware that Stockton had earlier made furious threats to shoot Flores if captured. So Flores thought it wise not to wait to be captured by the Americans. He handed his command to the one last officer he could trust, Andres Pico, and left for lower Mexico. Pico was also unable to see any other serious options to continue the fight. Fortunately, Californio Doña Barnarda Ruiz de Rodriguez from Santa Barbara, in hopes of avoiding any further bloodshed, contacted the camp to try to broker a surrender to a less-hostile Fremont, camped just north of Los Angeles. Pico agreed to meet with Fremont in the Cahuenga Pass to discuss terms for surrender. Pico was also motivated by the concern that, if captured by Kearny, he too would be executed to avenge the bloody and humiliating defeat his lancers earlier inflicted on Kearny and his men at San Pasqual. As newly-appointed Mexican Military Commander of California and the only significant Mexican authority left in California, Pico signed the Capitulation of Cahuenga with Colonel Fremont, effectively surrendering all of the Mexican province of Alta California to the United States.
A plaque presently marks the site of the Battle of the San Gabriel River. It is located at the northeast corner of Washington Boulevard and Bluff Road in Montebello.
Each January, the Montebello Historical Society and Juan Matias Sanchez Adobe Museum sponsors a commemoration of the Battle of the San Gabriel River with reenactors, musket fire demonstrations, displays, music and food.
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