Even though the two parties differ in their treatments of taxes and spending. I mean, since 1974 here's how california voted for pols/issues (source
http://en.wikipedia.org/wiki/Political_party_strength_in_California):
elected D president: every election since 1992
elected R president: 1976, 1980, 1984, 1988 (former CA governor Reagan in '80 and '84, Reagan's VP Bush in '88)
The three presidents from California were all Republican: Hoover, Nixon, and Reagan
elected D governor: 1974, 1978, 1998, 2002, 2010
elected R governor: 1982, 1986, 1990, 1994, 2003 recall, 2006
Both branches of legislature were majority D except when in 1995-1996 the Assembly had a slight Republican majority.
Social issues: voted for Prop. 187 ('94, no public school/services for unauthorized immigrants), Prop. 22 ('00, against gay marriage), Prop. 36 ('00, modifying 3 strikes law with drug treatment provision), Prop. 8 ('08 same but overturned in fed court and currently under judicial review). Specifically regarding cannabis use: for Prop. 215 ('96 for MEDICAL use only) but against Prop. 19 ('10, a tax and regulate marijuana initiative).
So I'd say CA is a rather purple state as the bluest parts are the Bay Area and LA yet there are conservative areas like Orange County, San Diego, and the Central Valley.