1. In 1851, the first Californian state constitutional convention was held in Monterey. Over 150 delegates gathered to create a document that would guide California as it transitioned from territory to statehood. The resulting constitution was ratified by the people and became the state's governing document until it was replaced in 1879.

2. On May 15, 1928, the St. Francis Dam in Los Angeles burst, causing a massive flood that killed over 500 people. The dam had been built by the city's chief engineer, William Mulholland, who had ignored warnings about its stability. This disaster led to increased regulation of dam construction in California and the United States.

3. The first commercial oil well in California was completed on May 15, 1865, in the town of Pico Canyon near Santa Clarita. The oil rush that followed transformed California's economy and helped it become a major player in the oil industry. Today, California remains the fourth-largest oil-producing state in the country.

4. In 1846, the Bear Flag Revolt began in Sonoma, an event that helped spark the Mexican-American War. A group of American settlers, led by William B. Ide, declared California to be an independent republic and raised a flag with a grizzly bear and a star on it. This revolt lasted for only a few weeks before American forces claimed California for the United States.

5. On May 15, 1969, the first legal floating casino in California opened for business on the SS Monte Carlo in Long Beach. The ship had previously been used as a gambling den in international waters before being towed into port and legalized by the city council. The Monte Carlo operated for several years before being shut down by the state authorities.