The Battle of La Mesa was the final battle of the California Campaign during the Mexican–American War, occurring on January 9, 1847, in present-day Vernon, California, the day after the Battle of Rio San Gabriel. The battle was a victory for the United States Army under Commodore Robert F. Stockton and General Stephen Watts Kearny.

Vernon is a city five miles (8.0 km) south of downtown Los Angeles, California, the nearest separate city to downtown Los Angeles. The population was 112 at the 2010 United States Census, the least of any incorporated city in the state. Its population nearly doubled to 222 by the 2020 census, making it the second least populous city in the state after Amador City, whose population grew only slightly—from 185 in the 2010 census, to 200 in the 2020 census.