Reagan was a cali native and also the hispanic population in Cali was growing since the 1980s due to immigration from across the border. The biggest switches were the future super liberal region of the bay area.
Yes, SF Bay Area and LA County turned decisively from Regan to Dukakis. Not sure if it was because Reagan was personally popular there or because Dukakis was a great cultural fit.
Demographics is destiny and the #1 reason why Dems have done well in presidential elections since 1992. Why do you think Dems want to import as many immigrans as freaking possible?