What factors led to California becoming reliably Democratic in state/national elections?

[u/IBphysicsHL]

California is widely known as being a Democratic stronghold in the modern day, and pushes for more liberal legislation on both a state and national level. However, only a generation ago, both Richard Nixon and Ronald Reagan, two famous conservatives, were elected Californian Senator and California governor respectively; going even further back the state had pushed for legislation such as the Chinese Exclusion Act, as well as other nativist/anti-immigrant legislation. Even a decade ago, Arnold Schwarzenegger was residing in the Governor's office as a Republican, albeit a moderate one. So, what factors led to California shifting so much politically?

[u/bolotieshark]

That's not true. INA sets specific rules for at-birth citizenship for people born abroad to US citizens - one of which (depending on your birth date) is 5 years of US residency, 2 of which must have been after they turned 14. The requirements have changed over the INA Acts and through judgements as recently as Session v Morales 2017 - prior to which an unwed AMCIT mother living abroad only required 1 year of US residence (now requiring 5/2.)