Detailed plan of the Battle of Rio San Gabriel (near modern day Montebello and Pico Rivera, the decisive Battle in the California Campaign, during the Mexican American War, from Emory's Survey.
After the Battle of San Pasqual, the Kearny went to the headquarters of Commodore Robert F. Stockton at San Diego. Stockton's next objective was to recapture Pueblo de Los Angeles. That settlement had been previously captured by Stockton's forces but was left in the command of Captain Archibald Gillespie and had been lost to the Californio militia, commanded by General José Mariá Flores.
Kearny and Stockton initially disputed the right of command. Although Kearny had superior orders from the United States War Department, he had previously sent most of his troops back to Santa Fe, New Mexico, believing that the war in California had ended, and his remaining force sustained heavy losses in the US defeat at the Battle of San Pasqual. Stockton had a larger force and was familiar with the area, so Kearny did not initially dispute Stockton's command of the campaign to recapture Los Angeles. Stockton departed San Diego in late December with a force of over 600 seamen and Marines, as well as Kearny's remaining force of about sixty dragoons.
U.S. scouts discovered the Mexican position on the San Gabriel River on January 7, 1847. Stockton and Kearny planned a crossing for the next day. The U.S. forces were formed into a hollow square with the artillery and baggage in the center. Kearny ordered the artillery unlimbered to cover the crossing, but Stockton countered the order and began to move across the river.
The U.S. 560 man force came under fire as it crossed, but because of a lack of sufficient guns and ammunition, and inadequate gunpowder, the Mexican artillery proved to be ineffective. The U.S. officers and men manhandled their cannon across while the forward quarter of the square took cover on the riverbank. Kearny led and commanded the assault force while Stockton stayed with the guns. The left flank of the square took a Mexican hilltop position and held it against a counterattack. Then the whole square charged forward shouting "New Orleans, New Orleans", in honor of Andrew Jackson's great victory against Great Britain there that day thirty-one years before. The charge took the heights, and Flores withdrew his smaller force. The battle had lasted an hour and a half, and while 8 Americans were wounded in the battle, as opposed to 7 Mexican casualties, the battle was decisive in the campaign for control of Los Angeles, and Alta California.