1. The Battle of San Pasqual: On December 16, 1846, the Battle of San Pasqual took place near Escondido in Southern California. The battle, which lasted for two hours, was fought between the United States Army and a group of Californios during the Mexican-American War. The Californios were successful in repelling the invasion and forcing the US forces to retreat. The battle is now considered a significant moment in California's history and is commemorated annually.

2. California's flag: December 16, 1846, is also the day when California first raised its distinctive bear flag at Sonoma. The bear flag has since become a symbol of California and is featured prominently on the state flag.

3. John Muir's birthday: John Muir, the influential naturalist and conservationist, was born on December 16, 1838, in Dunbar, Scotland. Muir is famous for founding the Sierra Club and for his work in preserving Yosemite Valley and other wilderness areas.

4. First transcontinental flight: On December 16, 1929, the first transcontinental flight in the United States took place, flying from New York to Los Angeles. The flight took 26 hours and 50 minutes to complete and was flown by TWA.

5. The Diamond Head eruption: On December 16, 1954, a spectacular eruption occurred at Diamond Head, a volcanic tuff cone located on the island of Oahu in Hawaii. The eruption produced a towering column of ash and gas, darkening the skies over Honolulu for several hours. This event is considered one of the most significant volcanic eruptions in Hawaii's recent history.