In the San Pasqual Valley southeast of Escondido, in the darkness of early morning on December 6, 1846, the American Army under Stephen Watts Kearny fought the bloodiest encounter to win California from Mexico. General Kearny and his 120 or so member Army of the West had just arrived from Missouri by way of New Mexico. Dreary, hungry, wet, and cold, they met and were defeated by a smaller force of Californios led by General Andres Pico who were waiting there to stop them from joining other American militants.

Suffering over 35 dead or wounded during the battle and under siege on Mule Hill, only the midnight escape by Kit Carson, Edward Beale, and an unnamed Indian averted their outright slaughter. The combined American force led by Commodore Robert Stockton then went on to win the Battle of San Gabriel on January 8 and January 9, 1847.

The San Pasqual battle was only one of the military encounters in California in the war, but it proved to be the bloodiest and most controversial as to the outcome. Today, a California State Monument commemorates the battlefield, and hundreds of volunteers reenact the event there on the Sunday closest to December 6.