San Ber·nar·di·no (sān bûr'nə-dē'nō, -nər-) A city of southern California at the foot of the San Bernardino Mountains east of Los Angeles. First explored in 1772, it was the site of a mission (established 1810) and a city founded by Mormons (1850s). It is a trade and processing center. Population: 199,000.