1. California's State Flag was Adopted on April 23, 1911: On this day, the State legislature officially adopted the state flag which features a grizzly bear and a single red star on a white backdrop.

2. The University of California, Riverside Was Established on April 23, 1954: UC Riverside is one of the 10 campuses of the University of California system and is located in Riverside County, California.

3. Jack Nicholson Was Born on April 22, 1937: The iconic actor, director, and screenwriter was born in Neptune City, New Jersey but moved to California when he was just a child.

4. Celebrate Earth Day on April 22, 1970: While not specifically a California holiday, Earth Day has become a worldwide celebration.

5. The First National Women's Health Week Began on April 23, 2005: This weeklong observance was created to raise awareness and encourage women to take control of their own health through preventative measures and regular check-ups.