1. The first California Pacific International Exposition opened in San Diego on May 19, 1935. The event was held in Balboa Park and attracted over 10 million visitors during its two-year run.

2. On May 19, 1846, John C. Frémont and his party arrived at the Bear Flag Revolt in Sonoma, California. This event marked the beginning of the Mexican-American War in California and ultimately led to the state's annexation by the United States.

3. The Golden Gate International Exposition opened on May 19, 1939, on Treasure Island in San Francisco Bay. Over 17 million people attended the fair during its two seasons, which were held in 1939 and 1940.

4. On May 19, 1869, a ceremony was held in Promontory Summit, Utah, to commemorate the completion of the first transcontinental railroad. The railroad linked the East Coast to California and helped transform the state's economy and demographics.

5. The California State Capitol was dedicated on May 19, 1874. The building, which is located in Sacramento, serves as the seat of government for the State of California and houses the offices of the governor, legislature, and other state officials.