"California were never independent nations."
The Bear Flag Republic was a briefly independent entity that resulted from the Revolt of 1846. The Republic was diplomatically recognized by US forces and a duly authorized plenopotentiary representative of the Russian Tsar so it is considered to have been a 'real' independent country as it was properly recognized by a disinterested third party power. Oddly, the Mexican Governor Mariano Guadalupe Vallejo favored annexation to the United States over the anti-American white settlers who wanted slavery to be legal in California. Vallejo alligned his interests with the USA and made possible a bloodless takeover of California by John C. Fremont who raised the Stars & Stripes in place of the Bear Flag.
Vallejo was later granted a pension by the State Legislature for his vision and loyalty to the United States.
The historical fact of how the Californios supported annexation to the USA also makes a lie of the myth that the USA 'stole' California from Mexico. The Californios (mostly of Spanish descent) wanted no part of the corrupt government in Mexico City and Vallejo actually raised a standing army in Sonoma to defend against the predations of the Mexican Army when it would raid farms for supplies and etc.
So, albeit briefly, California was an independent country.
The Bear Flag is now our state flag and that gives California the appropriate distinction of being the only state in the Union with a Red Star on its flag.
Vallejo is considered a "founding father" for some Californians.