1. On November 21, 1916, renowned artist Diego Rivera arrived in San Francisco to begin work on a mural commissioned by the San Francisco Art Institute. The mural, titled "Allegory of California," depicts the state's history and industries.

2. The famed Hollywood sign, originally constructed in 1923 as an advertisement for a real estate development called Hollywoodland, was officially dedicated on November 21 of that year.

3. On November 21, 1969, the first ARPANET message was transmitted from a computer at UCLA to a computer at the Stanford Research Institute, marking the birth of what would eventually become the internet.

4. In 1985, San Francisco's Moscone Center hosted the first "Hackers Conference," a gathering of computer enthusiasts, programmers, and visionaries. Among the attendees were Steve Jobs and Bill Gates.

5. In 2013, the California State Assembly passed a resolution officially recognizing November 21 as "Thanksgiving Day," urging Californians to celebrate and give thanks for the blessings of their lives.