A head to head comparison of the 2008 California General Election gives us an idea of the break down of the voters.    

Barack Obama received 8,274,473 (61%) votes, beating John McCain who gained 5,011,781 (37%) by 3,262,692 votes in California.

Barack Obama won 34 counties whereas John McCain won 24 counties in the total of the 58 counties in the State of California.

Presidential General Elections

During the 2008 General elections, over 131M total number of votes were cast. Barack Obama got 69,448,278 (69.4 Million) over John McCain's 61,739,059 (61.7 Million). He won the popular vote by 7,709,219 (7.7 Million). His victory in the State of California (with 8,274,473 votes) represents 10.6% of his popular vote victory. The remaining 49 states contributed to the remaining 89.4% popular votes victory.

Top 15 Counties in Primary Elections vs General Elections

All Candidates (General Elections)

These 15 counties play an important role in these Primary elections. If a candidate, can get a sizable majority in the largest counties (Los Angeles, San Diego, Orange, Santa Clara), it becomes very difficult to win majorities in the smaller counties without voter outreach and increased voter participation in them.

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
John McCain

Los Angeles, San Diego and Santa Clara, three of the larger counties voted in favor of Barack Obama, giving him a 1.1 Million vote advantage. Orange, another larger county voted in favor of John McCain giving him a 30k vote advantage. However, marginal wins for Barack Obama in the less popular counties (like Sonoma, San Mateo and more) were enough to maintain that difference, making him gain an upper hand in the State of California.

Related References: 2016 California Primary Election Story, 2016 California General Election Story, 2020 California Primary Election Story, 2020 California General Election Story, 2012 California General Election Story