1. California Gold Rush: On April 21, 1859, the first gold deposit was discovered in Carson Creek in California. This discovery led to a huge influx of people looking to strike it rich in California during the gold rush.

2. Earthquake: In 1966, a major earthquake struck California on April 21, measuring 6.7 on the Richter scale. It caused massive damage and killed dozens of people. This earthquake led to better preparation and building codes in California to prevent future disasters.

3. First Female Federal Judge: On April 21, 1980, Judge Judith N. Keep was appointed as the first female federal judge in California. She was appointed to the United States District Court for the Southern District of California.

4. California Indian Day: April 21 is recognized as California Indian Day, which celebrates the indigenous people of California and their culture. The day was established to acknowledge the contributions and resilience of Native Americans in California.

5. Yerba Buena Island Tunnel opens: On April 21, 1936, the Yerba Buena Island Tunnel was opened. It’s a two-bore, one-way tunnel 5400 feet long which connects the east and west lanes of San Francisco–Oakland Bay Bridge. This bridge made travel between the East Bay and San Francisco much easier, leading to more growth and prosperity in the region.