The interrogative phrase seeks to classify the status of September 11 within California. Legally, the correct classification is not a holiday. It is officially designated as a day of observance and remembrance known as Patriot Day, but it is not a judicial or state holiday where government offices and schools close.
California Government Code section 6700 enumerates the official state holidays, and September 11 is not included in this list. Instead, its status is defined by federal proclamation and mirrored in state-level observances. As Patriot Day, the date is marked by a directive for all United States flags to be flown at half-staff. California law also encourages public schools and educational institutions to conduct commemorative exercises to educate students about the historical significance of the date.
In practical terms, this designation means that September 11 is a regular business day in California. State and local government offices, courts, public schools, and private businesses operate on their normal schedules. The day's official status as a solemn observance does not provide for a paid day off for public or private sector employees.