National California Day is observed worldwide every February 22 to celebrate California’s admission to the Union as the 31st state. This day is part of the National State Days project, initiated in 2017 by National Day Calendar, which honors one state each week based on their admission order. California, known as the Golden State, is the most populous state in the U.S. and has a rich history that includes being inhabited by over 70 distinct indigenous groups before European colonization. The state was claimed by Spain in the 16th century, became part of Mexico in the 19th century, and was acquired by the U.S. following the Mexican-American War. The California Gold Rush significantly increased settlement in the region, leading to its statehood application in 1849 and eventual admission in 1850 after intense congressional debates. National California Day should not be confused with California Admission Day, which is celebrated on September 9.